BACKGROUND
when organisms are exposed to protein-denaturing stressors such as heat, the heat shock response  is engaged to manage protein damage and restore proteostasis  <cit> .
the hsr is highly conserved across species and is regulated by the transcription factor heat shock factor  <dig> .
during basal conditions, hsf <dig> exists as a monomer in the cytoplasm and nucleus, and during stress conditions undergoes trimerization and accumulation in the nucleus, where it binds to heat shock elements in the promoters of heat shock protein  genes  <cit> .
hsps primarily act as molecular chaperones which refold the misfolded proteins that accumulate during stress, but they can also have essential functions in protein synthesis, processing, and degradation  <cit> .
thus the hsr, and hsps, play a large role in maintaining organismal proteostasis.
the soil-dwelling, free-living, nematode caenorhabditis elegans is a powerful model organism that has provided insights into the regulation of a number of stress response pathways, including the hsr.
hsf- <dig>  the c. elegans homolog to mammalian hsf <dig>  contains conserved n-terminal dna-binding and trimerization domains, as well as a putative transactivation domain at the c-terminus  <cit> .
it has recently been shown that the same activity steps required for mammalian hsf <dig> activation, including trimerization, hyperphosphorylation, and induction of dna-binding, are also required for worm hsf- <dig> activation  <cit> .
studies in c. elegans show that hsf- <dig> plays a central role not only in the hsr, but also in contributing to organismal physiology.
hsf- <dig> is essential to worm viability, as a truncated mutant that lacks the c-terminal putative activation domain is defective in chaperone induction and egg laying, and also has a decreased lifespan  <cit> .
in addition, this strain has a temperature-sensitive developmental arrest phenotype, with arrest occurring at the l2-l <dig> transition  <cit> .
various experiments using hsf- <dig> rna interference  have shown that hsf- <dig> regulates the expression of specific hsp genes upon heat shock , and have also implicated a non-stress-induced role for hsf- <dig> in processes including development, metabolism, and longevity .
interestingly, studies in c. elegans have identified the hsr as a cell non-autonomous process that requires thermosensory neurons for hsp induction  <cit> .
upon the completion of sequencing of the c. elegans genome, over 40 % of the predicted protein products were found to be significantly conserved in other organisms  <cit> , and many signaling pathways are conserved  <cit> .
c. elegans is thus an excellent model system for studying the role of hsf- <dig> in stress responses and other physiological processes in a simple multicellular organism.
in this study, we have performed rna-sequencing  with synchronous larval stage l <dig> wild-type c. elegans fed empty vector  control rnai or hsf- <dig> rnai treated with or without hs.
we show that significant numbers of genes are upregulated as well as downregulated by hsf- <dig> under both conditions.
in addition to hsp genes, hsf- <dig> is required for the regulation of genes involved in a wide variety of cellular processes including cytoprotection, development, metabolism, and aging.
network analysis points to possible routes by which hsf- <dig> signaling may be coordinated across tissues.
a nuclear hormone receptor may coordinate the hs-induced hsf- <dig> transcriptional response, while an epidermal growth factor receptor may coordinate the hs-independent response.
surprisingly, the top hsf-1-regulated gene category, both with and without heat stress, is cuticle structure.
this result, together with other recent studies, thus links regulation of the extracellular matrix to hsf- <dig>  cytoprotection, and longevity.
RESULTS
experimental set-up for genome-wide analysis of regulation of gene expression by hsf-1
previous experiments have shown that hsf- <dig> regulates the expression of specific hsp genes upon hs, and have also implicated a non-stress-induced role for hsf- <dig> in development, metabolism, and longevity .
to examine hs-dependent vs. -independent gene regulation by hsf- <dig> on a genome-wide level, we used whole transcriptome rna-sequencing.
we treated synchronous l <dig> larval stage nematodes with rnai against hsf- <dig>  or with an ev control plasmid  until the l <dig> larval stage.
at the l <dig> stage, we then treated nematodes from both groups with or without a 30 min 33 °c hs, as diagrammed .
experiments were performed in biological duplicates.
the l <dig> stage was chosen for our studies as this is a time when the response to hs is strong, prior to a sharp decline that occurs shortly after the transition to adulthood  <cit> .
these treatment conditions, optimized for our studies, resulted in a ~9- log2-fold induction of the hsp- <dig> gene c12c <dig> , a classical hsf- <dig> target gene, in hsf- <dig> animals treated with hs .
as expected, rnai against hsf- <dig> blunted hsp- <dig> induction by hs .
the efficiency of our rnai feeding strategy was assessed by testing the effects of hsf- <dig> rnai on transcription driven by two heat shock protein promoter- gfp reporter worm strains .
hs increases gfp expression, and this effect is dependent on hsf- <dig> as demonstrated with hsf- <dig> rnai.
using an hsf-1::gfp overexpression worm strain, we also show that hsf- <dig> protein levels are reduced 80 % in response to hsf- <dig> rnai treatment .
overall, these data validate our hs treatment conditions and rnai feeding strategy.
cluster analysis performed on biological replicate rna-seq samples revealed conserved patterns of expression induced by each treatment condition .
we normalized each condition to the hsf-1;-hs control in order to determine fold changes in relative rna abundance .
a complete list of the significant genes altered in response to each condition, after normalization to the control, is also provided .
volcano plot analyses show that while a limited group of genes for each comparison have a log2-fold change of  <dig> or higher, the majority of genes have a log <dig> -fold change of approximately  <dig> or less .
as growth temperature and hsf- <dig> expression levels can affect the rate of development in the worm  <cit> , we verified that our observed gene expression changes were not simply due to a change in the rate of development between each treatment condition.
to do this, we analyzed several genes that are known to be differentially expressed during development and molting, including abu- <dig>  wrt- <dig>  his- <dig>  lin- <dig>  abu- <dig>  abu <dig>  pqn- <dig>  pin- <dig>  ptr- <dig>  abu- <dig>  abu- <dig>  and sdz- <dig>  <cit> , and detected no significant expression differences in these genes across treatment groups .
overall, our data indicate that the worms in our four treatment conditions are developmentally synchronous to one another, and that the biological replicates for each condition share a similar expression profile, thus validating our experimental conditions.
next, to visualize total hs-dependent vs. -independent gene expression regulated by hsf- <dig>  we constructed a venn diagram with the differentially expressed genes for each condition which were determined to be statistically significant as compared to the hsf-1;-hs control .
the shaded areas of the venn diagram correspond to hs-dependent and -independent processes regulated by hsf- <dig> , and these are the transcripts that we have focused our subsequent analyses on.
altogether, we found that  <dig> genes are significantly regulated by hsf- <dig> during hs , and that  <dig>  genes are significantly regulated by hsf- <dig> independently of hs , highlighting that hsf- <dig> regulates both hs-dependent and -independent transcriptional processes.
interestingly, only  <dig> genes are significantly regulated by hs independently of hsf- <dig>  hsf- <dig> is thus not only an essential transcriptional regulator for a majority of the genes altered by hs, but global rna expression analysis supports a gene-regulatory role for hsf- <dig> under both heat stress and non-stress conditions.
a greater number of gene changes that depend on hsf- <dig> are independent of heat stress, thus highlighting the important role of hsf- <dig> in regulating gene expression under non-stress conditions.
genes that are regulated by hsf- <dig> in response to hs
genes that are normally upregulated by hsf- <dig> in response to hs
to determine whether hsf- <dig> can affect gene expression in both a positive and negative fashion, we separated out the positively vs. negatively regulated genes and analyzed them by venn diagram.
we find that  <dig> transcripts are normally upregulated by hsf- <dig> upon hs .
we next examined these  <dig> genes in more depth.
the top  <dig> genes in this category are listed in table  <dig> .
included in the top  <dig> upregulated transcripts are  <dig> hsp- <dig> family genes and  <dig> hsp- <dig> family genes, all with log2-fold changes greater than  <dig>  the presence of chaperone genes in our top  <dig> hits was expected, and gave us confidence in our experimental strategy.
aside from chaperone genes, there are a number of non-chaperones included in the top  <dig> most upregulated genes, including the nucleosome remodeling factor complex member nurf- <dig>  <cit> , the predicted collagen gene col- <dig>  and various genes of unknown function .
therefore, the top  <dig> genes regulated by hsf- <dig> under hs conditions include  <dig> hsp genes and  <dig> genes with diverse functions.fig.
<dig> genes that are normally upregulated by hsf- <dig> in response to hs.
a the venn diagram shows the overlap among genes that were found to be significantly upregulated  for each of the indicated comparisons between samples.
the dark blue shaded area includes genes that are normally upregulated by hsf- <dig> upon hs.
the q-value is the fdr-adjusted p-value of the test statistic, as determined by the benjamini-hochberg correction for multiple testing.
b hierarchical clustering of the genes normally upregulated by hsf- <dig> upon hs.
lane  <dig> corresponds to the fold change of the  <dig> genes found in the dark blue section of the venn diagram in  in the hsf-1;+hs vs. control samples.
as a comparison, lane  <dig> corresponds to the fold change of the same genes found in lane  <dig>  but in the hsf-1;+hs vs. control samples, as determined by rna-seq.
the heat map was organized using cluster  <dig> by k-means and euclidean distance.
c top processes normally upregulated by hsf- <dig> during hs.
the genes found in the dark blue section of the venn diagram in  were classified by gene ontology terms that were determined using david
f44e <dig>
f44e <dig>
f44e <dig>
f44e <dig>
y46h3a.3
hsp- <dig>
y46h3a.2
hsp- <dig>
t27e <dig>
hsp- <dig>
c12c <dig>
hsp-70
t27e <dig>
hsp- <dig>
t27e <dig>
hsp- <dig>
y38e10a.13
nspe-1
t27e <dig>
hsp- <dig>
f26h <dig>
nurf-1
zc <dig>
zc <dig>
d <dig>
scp-1
r <dig>
r <dig>
b <dig>
col-149
the transcript id, gene name, fold change as compared to the hsf-1;-hs control, and description as provided from wormbase, are listed for the  <dig> genes with the highest positive fold changes in expression.
a complete list of significantly upregulated transcripts is given
we then further examined the induction characteristics of the top  <dig> hsf-1-dependent genes induced by hs.
the log2-fold changes for a subset of these genes are plotted  and compared to the expression of the same genes in the presence of hs but in the absence of hsf- <dig> .
the fact that hsf- <dig> rnai completely eliminates hs-inducibility of these genes highlights their dependency on hsf- <dig>  independent quantitative rt-pcr  for the same subset of highly induced genes  validates our rna-seq data.
in order to better visualize the global patterns of transcript upregulation by hsf- <dig> in response to hs, we constructed a heat map of the  <dig> significantly upregulated genes .
interestingly, and consistent with the data for a set of the top  <dig> upregulated genes , genes that are normally upregulated by hsf- <dig> upon hs are either unchanged or downregulated under hs conditions upon hsf- <dig> knockdown on a global level .
the fact that many of the  <dig> hs-induced genes that require hsf- <dig> are downregulated upon hsf- <dig> knockdown implies that hsf- <dig> may play a role in the basal regulation of these genes, which is then enhanced upon hs.
together, these data demonstrate the hsf- <dig> dependency of most hs-induced genes.
to identify the various functional processes normally upregulated by hsf- <dig> during hs, we used the database for annotation, visualization, and integrated discovery  classification tool to define the top  <dig> gene ontology terms for all of the  <dig> genes found to be significantly upregulated .
the complete output from david is also provided .
surprisingly, the top functional category, with an enrichment score of  <dig>  contains genes involved in cuticle structure.
the next four categories, all with enrichment scores under  <dig>  include genes involved in translation, the response to stress, the regulation of growth, and amine catabolic processes.
we thus find that the largest functional category of genes regulated by hs is not the expected heat stress-responsive gene-set, but instead genes associated with forming cuticle structure.
we next tested the effects of a cuticle collagen gene, col- <dig>  on induction of the hsr by measuring hsp- <dig> promoter activity in phsp-70::gfp worms .
we see that col- <dig> rnai decreases hs-induced hsp- <dig> promoter activity, and may control tissue-specific regulation of the hsr.
testing the effects of other collagen genes on regulation of the hsr may provide insight into a signaling role for collagens in coordinating stress responses.
genes that are normally downregulated by hsf- <dig> in response to hs
we next examined the genes separated out from the venn diagram analysis to be normally downregulated by hsf- <dig> upon hs .
we find that there are  <dig> transcripts in this group .
the top  <dig> genes normally downregulated by hsf- <dig> upon hs are listed in table  <dig> .
there are a variety of distinct transcripts downregulated by hsf- <dig> during hs.
the gene with the largest log2-fold decrease  is acs- <dig>  which encodes an acyl-coa synthetase.
this enzyme participates in breakdown of fatty acids into acyl-coa in the mitochondria to allow for β-oxidation, thus increasing fat consumption  <cit> .
another downregulated gene is dct- <dig>  which encodes a protein that has pro-apoptotic activity  <cit> .
the tetraspanin family member tsp- <dig> is also downregulated.
the tetraspanin family of proteins is required for epithelial integrity in the worm and regulates cuticle formation  <cit> .
other downregulated genes include fbxa- <dig> and fbxa- <dig>  which encode fboxa proteins with unknown functions; nep- <dig>  which encodes a zinc metallopeptidase that negatively regulates signaling peptides  <cit> ; glc- <dig>  which encodes a subunit of a glutamate-gated chloride channel  <cit> ; and delm- <dig>  which encodes an ortholog of an acid-sensing ion channel family member  <cit> .
there are also multiple transcripts of unknown function in this gene group.
therefore, the top  <dig> genes normally downregulated by hsf- <dig> under hs conditions have a diverse set of functions.fig.
<dig> genes that are normally downregulated by hsf- <dig> in response to hs.
a the venn diagram shows the overlap among genes that were found to be significantly downregulated  for each of the indicated comparisons between samples.
the dark purple shaded area includes genes that are normally downregulated by hsf- <dig> upon hs.
the q-value is the fdr-adjusted p-value of the test statistic, as determined by the benjamini-hochberg correction for multiple testing.
b hierarchical clustering of the genes normally downregulated by hsf- <dig> upon hs.
lane  <dig> corresponds to the fold change of the  <dig> genes found in the dark purple section of the venn diagram in  in the hsf-1;+hs vs. control samples.
as a comparison, lane  <dig> corresponds to the fold change of the same genes found in lane  <dig>  but in the hsf-1;+hs vs control samples, as determined by rna-seq.
the heat map was organized using cluster  <dig> by k-means and euclidean distance.
c top processes normally downregulated by hsf- <dig> during hs.
the genes found in the dark purple section of the venn diagram in  were classified by gene ontology terms that were determined using david
f28f <dig>
acs-2
w09g <dig>
w09g <dig>
c07a <dig>
c07a <dig>
c14f <dig>
dct-1
c02f <dig>
tsp-1
y54f10bm.11
fbxa-66
y119d3b.9
fbxa-21
k08d <dig>
k08d <dig>
c49g <dig>
c49g <dig>
t12a <dig>
t12a <dig>
f33h <dig>
f33h <dig>
y47h10a.5
y47h10a.5
zk <dig>
nep-26
f11a <dig>
glc-1
c24g <dig>
delm-2
the transcript id, gene name, fold change as compared to the hsf-1;-hs control, and description as provided from wormbase are listed for the  <dig> genes with the highest negative fold changes in expression.
a complete list of significantly downregulated transcripts is given
we then further studied the top  <dig> genes that are normally downregulated by hsf- <dig> upon hs.
the log2-fold changes of a subset of the top  <dig> hsf-1-dependent genes repressed by hs are plotted , and these data are compared to the expression of the same genes in the presence of hs but in the absence of hsf- <dig> .
interestingly, we found that all of the genes that are downregulated by hs in the presence of hsf- <dig> are upregulated by hs in the absence of hsf- <dig>  one way this could occur is if hsf- <dig> normally suppresses the expression of these genes, and hs-activated hsf- <dig> suppresses them even further.
to verify our rna-seq data, we performed independent qrt-pcr for the same subset of highly downregulated genes, and found that the qrt-pcr data was consistent with our rna-seq data .
to visualize the patterns of transcripts that are normally downregulated by hsf- <dig> upon hs, we constructed a heat map to visualize the log2-fold changes of the  <dig> significantly downregulated genes .
as a comparison, the expression of the same transcripts under hs conditions upon hsf- <dig> knockdown is shown .
as with the data for the top downregulated genes , many of the  <dig> genes that are normally downregulated by hsf- <dig> under hs conditions are conversely upregulated by hs in the absence of hsf- <dig>  thus, hs can have completely opposite effects on gene expression depending on the presence or absence of hsf- <dig>
upon david analysis of gene ontology terms for the repressed genes, the top  <dig> functional categories all had enrichment scores of  <dig> or lower.
these functional categories include genes that encode proteins with kinase activity, ion binding activity, transcription, atp-binding activity, and reproductive development .
the complete output from david is also provided .
overall, these results show that a diverse group of genes are normally suppressed by hsf- <dig> during hs.
genes that are regulated by hsf- <dig> independently of hs
genes that are normally upregulated by hsf- <dig> independently of hs
while hsf- <dig> has been historically studied for its role in regulating responses elicited by hs, hsf- <dig> also has functions that are independent of hs including roles in development, metabolism, and longevity .
to identify processes upregulated by hsf- <dig> independently of hs, we examined the  <dig>  genes from the venn diagram that we determined to be downregulated in response to hsf- <dig> rnai independently of hs, suggesting that they are normally upregulated by hsf- <dig> .
in order to gain insight into the normal hsf-1-regulatory role of these hs-independent genes, we reversed our data comparison  to obtain the fold change, as this gene group is shown to be downregulated in response to hsf- <dig> rnai and would thus normally be upregulated by hsf- <dig> fig.
<dig> genes that are normally upregulated by hsf- <dig> independently of hs.
a the venn diagram shows the overlap among genes that were found to be significantly downregulated  for each of the indicated comparisons between samples.
the light purple shaded area includes genes that are downregulated upon treatment with hsf- <dig> rnai, and are likely normally induced by hsf- <dig> independently of heat shock, therefore are referred to as upregulated genes.
the q-value is the fdr-adjusted p-value of the test statistic, as determined by the benjamini-hochberg correction for multiple testing.
b hierarchical clustering of the genes normally upregulated by hsf- <dig> independently of hs.
the fold change of genes found in the light purple section of the venn diagram in  were determined by rna-seq to be downregulated in response to hsf- <dig> rnai, and would thus normally be upregulated by hsf- <dig>  lane  <dig> corresponds to the fold change of these genes in the control vs. hsf-1;-hs samples, and as a comparison, lane  <dig> corresponds to each the fold change of the same genes found in lane  <dig> but in the control vs. hsf-1;+hs samples.
the heat map was organized using cluster  <dig> by k-means and euclidean distance.
c top processes normally upregulated by hsf- <dig> independently of hs.
the genes found in the light purple section of the venn diagram were classified by gene ontology terms that were determined using david
the top  <dig> genes that are normally upregulated by hsf- <dig> under non-stress conditions are listed in table  <dig> .
surprisingly, a group of vitellogenin lipid transporter transcripts  are among the top  <dig> genes.
vitellogenins are made in the intestine of late larval/early adult hermaphrodites and are taken up by the germ cells to provide nourishment to embryos  <cit> .
other top upregulated genes include acdh- <dig>  which encodes a short chain acyl-coa dehydrogenase and may play a role in energy production  <cit> ; k11g <dig> , which is predicted to be an ortholog of human butyrylcholinesterase; folt- <dig>  which encodes a folate transporter  <cit> ; ilys- <dig>  which is predicted to have lysozyme activity; zc <dig> , which is predicted to have g-protein coupled receptor activity; fat- <dig>  which encodes a fatty acid desaturase  <cit> ; k10b <dig> , which is predicted to have carboxypeptidase activity; y52e8a.
<dig>  which encodes the ortholog to a major facilitator superfamily; ugt- <dig>  which encodes the ortholog of a polypeptide predicted to have transferase activity; and two genes with unknown function.
therefore, a diverse set of genes, including vitellogenins and others, are normally upregulated by hsf- <dig> independently of hs.table  <dig> top  <dig> genes normally upregulated by hsf- <dig> independently of hs
c55b <dig>
acdh-1
f59d <dig>
vit-3
f59d <dig>
vit-4
c04f <dig>
vit-5
k09f <dig>
vit-1
y40h7a.10
y40h7a.10
k11g <dig>
k11g <dig>
f37b <dig>
folt-2
f22a <dig>
ilys-5
zc <dig>
zc <dig>
f10d <dig>
fat-7
k10b <dig>
k10b <dig>
y52e8a.4
y52e8a.4
c08f <dig>
ugt-22
f54f <dig>
f54f <dig>
the transcript id, gene name, and fold change in gene expression in the comparison of the control vs. hsf-1;-hs are listed for the top  <dig> genes normally upregulated by hsf- <dig> independently of hs.
gene descriptions, as provided from wormbase, are also listed.
a complete list of the significantly altered transcripts is given
we then further characterized the induction characteristics of the top  <dig> genes that are normally upregulated by hsf- <dig> independently of heat stress.
the log2-fold changes of a subset of these top  <dig> genes are plotted , and are compared to the expression of the same genes in the presence of hs and absence of hsf- <dig> .
this data shows that hs does not affect the expression of these genes in the absence of hsf- <dig>  the expression of these mrnas was also verified with qrt-pcr, and the results are consistent with the rna-seq data .
to investigate a hs-independent role for hsf- <dig> in the induction of gene expression on a global level, we generated a heat map of all  <dig>  genes found via venn diagram to be normally upregulated by hsf- <dig> in the absence of hs .
as a comparison, genes that are normally upregulated by hsf- <dig> in the presence of hs are plotted .
the transcripts in this group that are normally upregulated by hsf- <dig> in the absence of hs remain upregulated or unchanged in the presence of hs, verifying the heat stress-independent induction of this gene group.
we next used david to determine the top  <dig> functional processes that are normally upregulated by hsf- <dig> independently of hs.
we found that cuticle structure was again the gene category with the highest enrichment score , as was also the case for the genes that are upregulated by hsf- <dig> during hs .
this indicates that hsf- <dig> may regulate the basal expression of genes involved in cuticle structure, and that these genes are then further induced upon hs.
other functional processes, with enrichment scores less than  <dig>  include genes that encode proteins involved in the mitochondrial envelope, acyl-coa dehydrogenase activity, peptidase activity, and oxidoreductase activity.
the complete output from david is also available .
the mitochondrial envelope, acyl-coa dehydrogenase activity, peptidase activity, and oxidoreductase activity are all processes that can be linked to metabolism, further substantiating a functional role for hsf- <dig> in regulating this process.
genes that are normally downregulated by hsf- <dig> independently of hs
we next examined the  <dig>  genes from the venn diagram that we determined to be upregulated in response to hsf- <dig> rnai independently of hs, suggesting that they are normally downregulated by hsf- <dig> .
we reversed our data comparison  to obtain the fold change, as this gene group is shown to be upregulated in response to hsf- <dig> rnai and would thus normally be downregulated by hsf- <dig>  the top  <dig> genes in this category are listed in table  <dig> .
there are a variety of transcript types in this list, including t22f <dig> , which is an mrna that encodes the ortholog of the human solute carrier family 17; eol- <dig>  which regulates olfactory learning  <cit> ; bo <dig> , which encodes an ortholog of human lipopolysaccharide-induced tnf factor; col- <dig>  which encodes a structural constituent of the cuticle; fbxa- <dig> and t08e <dig> , which encode proteins that contain f-box motifs predicted to be important for protein-protein interactions; clec- <dig> and clec- <dig>  which encode carbohydrate binding proteins; srg- <dig>  which encodes a protein involved in embryo development; clec- <dig>  which encodes a protein involved in the immune response; b <dig> , which encodes an ortholog of human cingulin-like 1; clec- <dig>  which is predicted to have carbohydrate binding activity; f22f <dig> , which encodes an ortholog of human grb <dig> interacting gyf protein 2; and y47h10a.
<dig> and zk <dig> , which both have unknown functions.
overall, we find that a diverse set of mrnas are normally downregulated by hsf- <dig> independently of hs, indicating that hsf- <dig> may normally suppress a variety of cellular processes in a hs-independent manner.fig.
<dig> genes that are normally downregulated by hsf- <dig> independently of hs.
a the venn diagram shows the overlap among genes that were found to be significantly upregulated  for each of the indicated comparisons between samples.
the light blue shaded area includes genes that are upregulated upon treatment with hsf- <dig> rnai, and are likely normally suppressed by hsf- <dig> independently of heat shock, therefore are referred to as downregulated genes.
the q-value is the fdr-adjusted p-value of the test statistic, as determined by the benjamini-hochberg correction for multiple testing.
b hierarchical clustering comparing the genes normally suppressed by hsf- <dig> independently of hs.
the fold change of genes found in the light blue section of the venn diagram in  were determined by rna-seq to be upregulated in response to hsf- <dig> rnai, and would thus normally be suppressed by hsf- <dig>  lane  <dig> corresponds to the fold change of these genes in the control vs. hsf-1;-hs samples, and as a comparison, lane  <dig> corresponds to each the fold change of the same genes found in lane  <dig> but in the control vs. hsf-1;+hs samples.
the heat map was organized using cluster  <dig> by k-means and euclidean distance.
c top processes normally downregulated by hsf- <dig> independently of hs.
the genes found in the light blue section of the venn diagram were classified by gene ontology terms that were determined using david
t22f <dig>
t22f <dig>
t26f <dig>
eol-1
b <dig>
b <dig>
y47h10a.5
y47h10a.5
d <dig>
col-158
c08e <dig>
fbxa-163
f07e <dig>
f07e <dig>
y46c8al.2
clec-174
t07h <dig>
srg-31
zk <dig>
clec-60
b <dig>
b <dig>
zk <dig>
zk <dig>
h16d <dig>
clec-13
t08e <dig>
t08e <dig>
f22g <dig>
f22g <dig>
the transcript id, gene name, and fold change in gene expression in the comparison of the control vs hsf-1;-hs are listed for the top  <dig> genes normally downregulated by hsf- <dig> independently of hs.
gene descriptions, as provided from wormbase, are also listed.
a complete list of the significantly altered transcripts is given
the induction characteristics of the top  <dig> genes in this category were then analyzed.
the log2-fold changes from the rna-seq data for a subset these genes are plotted , and are compared to the expression of the same genes in the presence of hs in the absence of hsf- <dig> .
the expression of these mrnas was also verified with qrt-pcr, and the results are consistent with the rna-seq data .
altogether, these data confirm that hs does not affect the expression of these genes in the absence of hsf- <dig>
to investigate a hs-independent role for hsf- <dig> in the suppression of gene expression, we constructed a heat map of all  <dig>  genes found via venn diagram to be normally suppressed by hsf- <dig> in the absence of hs .
as a comparison, the expression patterns of the same transcripts suppressed by hsf- <dig> in the presence of hs are shown .
the transcripts in this group that are significantly downregulated by hsf- <dig> in the absence of hs remain downregulated or unchanged by hsf- <dig> in the presence of hs, further verifying that regulation of this subset of genes by hsf- <dig> is independent of hs.
we next used david to determine the functional processes that are normally downregulated by hsf- <dig> independently of hs.
genes involved in cell cycle processes were most abundant, with an enrichment score of  <dig>  followed by genes involved in epithelium development, regulation of growth, genitalia development, and cell migration, all with enrichment scores under  <dig> .
the complete output from david is also available .
cell cycle processes, epithelium development, regulation of growth, genitalia development, and cell migration are all processes that can be linked to development, thus confirming a hs-independent role for hsf- <dig> in development.
discussion
regulation of gene expression by hsf-1
c. elegans is a useful model organism for identifying regulatory processes that are shared between species.
while the transcription factor hsf- <dig> has classically been studied as a factor that is responsive to cytoplasmic proteotoxic stress, it is becoming increasingly evident that this transcription factor also has major non-stress-induced roles in coordinating gene expression.
with the rna-sequencing experiments performed here, we confirm that hsf- <dig> can regulate gene expression under both heat stress and non-stress conditions.
in addition to genes that are classically stress-responsive, such as chaperones, our work shows that hsf- <dig> also regulates sets of genes involved in a variety of cellular processes including metabolism, development, and longevity.
cuticle structure genes are normally upregulated by hsf- <dig> via hs-dependent and -independent mechanisms
a surprising result of our study is that genes controlling cuticle structure comprise the largest gene ontology group that is upregulated by hsf- <dig> in both a hs-dependent and -independent manner.
the c. elegans cuticle is an exoskeletal structure that creates a barrier between the animal and the environment, provides body shape, and allows movement via attachment to muscle.
many of the genes in the cuticle structure category are collagens, structural proteins that form an extracellular matrix composing the exoskeleton, or cuticle, of the nematode.
there are ~ <dig> distinct collagen genes in c. elegans, and they are expressed in a tissue-specific fashion and at distinct temporal times  <cit> .
cuticle structure is controlled by enzymes involved in collagen processing, and the polymerization pattern is dictated by actin filaments that are organized in specific patterns around the body of the worm.
in humans, collagens comprise about one-third of all expressed protein  <cit> .
aside from the structural role of collagens, these genes can also participate in signal transduction .
collagen genes were recently found to be upregulated by skn- <dig>  the c. elegans oxidative stress-responsive transcription factor  <cit> .
in future work, it will be interesting to test whether collagen can act to relay signals to stress-specific transcription factors including skn- <dig> and hsf- <dig>
roles for hsf- <dig> in regulating metabolism and development in a hs-independent manner
although hsf- <dig> has classically been studied as a transcription factor that responds to hs and cytoplasmic proteotoxic stress, hsf- <dig> has recently been gaining importance as a transcription factor that is involved in non-stress processes including development and metabolism  <cit> .
in mice, hsf family members have been documented to be involved in diverse developmental processes, including oogenesis, spermatogenesis, and corticogenesis  <cit> .
hsf- <dig> in the worm has also been shown to be regulated by insulin/igf- <dig>  tgf-β, and cgmp signaling to control development  <cit> .
the finding that mammalian hsf <dig> can be regulated by sirt <dig>  a deacetylase that is under metabolic control, provides evidence that hsf- <dig> and metabolism are linked  <cit> .
this finding is also true for c. elegans hsf- <dig>  as the sirt <dig> homolog sir- <dig>  regulates the c. elegans hsr  <cit> .
additionally, the insulin-like signaling regulators ddl-1/ <dig> have been linked to hsf- <dig> regulation  <cit> .
here, we show that under non-stress conditions, hsf- <dig> regulates a number of genes involved in developmental and metabolic processes.
therefore, our work further highlights the links between hsf- <dig> and these non-stress processes.
network analysis identifies a nuclear hormone receptor as a common link between processes regulated by hsf- <dig> upon hs
to determine how the genes regulated by hsf- <dig> during hs may interact with each other, we performed network analysis using genes associated with the top go-terms as determined by david .
we used the mimi plugin to integrate data from protein interaction databases  to allow for the creation of interaction networks using the network-building software cytoscape.
this analysis enabled us to identify interacting partners shared by at least two genes regulated by hsf- <dig> during hs.
the transcripts induced by hsf- <dig> during hs are shown in red, while the transcripts downregulated by hsf- <dig> during hs are shown in blue, with the intensity of color correlating to the fold change.
genes that are not colored were not found to be affected by hsf- <dig> during hs in our dataset, but are neighbors shared by at least two genes that were affected.
we found network linkages between the processes of cuticle structure formation, translation, the response to stress, protein kinase activity, and transcription .
interestingly, the nuclear hormone receptor nhr- <dig> is a common link between several of the hs-regulated processes that require hsf- <dig>  including cuticle structure, translation, and the response to stress.
nuclear hormone receptors comprise a class of ligand-gated transcription factors that bind to small molecule metabolites such as fatty acids, vitamins, and steroids to directly regulate gene transcription  <cit> .
they are thus well-poised to coordinate metabolism, development, reproduction, and homeostasis across diverse tissues.
nhr- <dig> is broadly expressed in c. elegans and is located in eight head neurons, the sensory pvd neurons in the posterior lateral body wall, the pharynx, the intestine, the dorsal peri-vulva region, and the somatic gonad precursor cells  <cit> .
in future work, it will be interesting to test the role of nhr- <dig> and other nuclear hormone receptors in the hsr, and to see if it can contribute towards the coordination of this response across tissues.fig.
<dig> network analyses of the top hsf-1-regulated processes.
a predicted network regulated by hsf- <dig> during hs.
genes associated with the top  <dig> induced and suppressed processes in figs.
1c and 2c were used for analysis.
b predicted network regulated by hsf- <dig> independently of hs.
genes associated with the top  <dig> induced and suppressed processes in figs.
3c and 4c were used for analysis.
for a and b, the color of each gene corresponds to the degree of hsf- <dig> regulation of the corresponding transcript.
network analysis was done with mimi using the cytoscape platform.
the uncolored genes were not affected by hsf- <dig> during or independently of hs in our dataset, but are neighbors shared by at least two genes that were affected in our dataset
network analysis identifies a tyrosine kinase as a common link between various developmental processes regulated by hsf- <dig> independently of hs
to uncover c. elegans interaction networks associated with processes regulated by hsf- <dig> independently of hs, we performed network analysis using genes associated with the top go-terms as determined by david .
network linkages were found for genes involved in the mitochondrial envelope, peptidase activity, oxidoreductase activity, cell cycle processes, and epithelium development.
we found that let- <dig>  an epidermal growth factor receptor tyrosine kinase   <cit> , is predicted to interact with many of these transcripts.
the egf pathway in c. elegans has been linked to multiple developmental pathways  <cit> .
this rtk may thus allow for signaling to hsf- <dig> during non-stress conditions to modulate developmental gene expression.
interestingly, hsf <dig> null mouse embryonic fibroblasts are defective in both basal and egf-induced cell migration  <cit> , so the link between hsf- <dig> and the egf signaling pathways may be conserved across species.
it will thus be worthwhile in future work to test for the involvement of let- <dig> in the regulation of hsf- <dig> activity in c. elegans.
hsf- <dig> impacts aging-regulated gene expression
as hsf- <dig> has been implicated to play an important role in both aging and disease  <cit> , we analyzed the role of hsf- <dig> in regulating age-associated transcriptional changes in our data-sets .
by comparing the transcriptome profiles between young and old adult c. elegans, a previous study by budovskaya et al.
identified  <dig>  genes to be differentially regulated upon worm aging  <cit> .
a venn diagram comparison of these  <dig>  age-regulated genes with those that we found to be regulated by hsf- <dig> during hs shows that  <dig> aging-associated genes overlapped with our dataset .
a complete list of genes shared between both data-sets is also provided .
the functional processes regulated by this overlapping gene set were then determined via david analysis.
cuticle structure was the largest functional category, with an enrichment score of  <dig> .
other gene categories, all with enrichment scores of  <dig> or lower, include cuticle development, the response to stress, amine catabolic processes, carbohydrate binding, and membrane structure.
network analysis performed on the  <dig> overlapping genes shows that only a small subset of these genes are predicted to interact with each other .fig.
<dig> age-regulated genes controlled by hsf- <dig>  a the venn diagram shows the overlap among genes that are differentially expressed during aging and regulated by hsf- <dig> during hs.
the venn diagram was made using genes previously found to be regulated during aging by budovskaya et al.
compared to genes we found to be regulated by hsf- <dig> during hs.
b cellular processes affected by aging and hsf- <dig> during hs.
genes shared between the aging dataset and hsf-1-regulated hs-dependent dataset from  were analyzed with david and the gene ontology terms are listed in order of decreasing enrichment.
c network analysis of the genes regulated by aging and hsf- <dig> during hs.
network analysis was done with mimi using the cytoscape platform and the transcripts shared between data-sets .
the color of each transcript corresponds to the degree of hsf- <dig> regulation.
genes that are not colored were not affected by hsf- <dig> our dataset, but are neighbors shared by at least two genes that were affected in our dataset.
d the venn diagram shows the overlap among genes that are differentially expressed during aging and regulated by hsf- <dig> independently of hs.
the venn diagram was made using genes previously found to be regulated during aging by budovskaya et al.
compared to genes we found to be regulated by hsf- <dig> independently of hs.
e cellular processes affected by aging and hsf- <dig> independently of hs.
genes shared between the aging dataset and hsf-1-regulated hs-independent dataset from  were analyzed with david and the gene ontology terms are listed in order of decreasing enrichment.
f network analysis of the genes regulated by aging and hsf- <dig> independently of hs.
network analysis was done with mimi using the cytoscape platform and the transcripts shared between data-sets .
the color of each transcript corresponds to the degree of hsf- <dig> regulation.
genes that are not colored were not affected by hsf- <dig> in our dataset, but are neighbors shared by at least two genes that were affected in our dataset
next, a comparison between aging-associated genes and those we found to be regulated by hsf- <dig> independently of hs was done.
a venn diagram shows that  <dig> aging-associated genes overlapped with our dataset .
a complete list of genes shared between both data-sets is also provided .
the functional processes regulated by this gene set was then determined via david analysis.
cuticle structure was again the largest category, with an enrichment score of  <dig>  the other categories, with enrichment scores of  <dig> or lower, include peptidase activity, c-type lectin, vitamin binding, and lifespan-associated processes .
the transcriptional impact of these hsf- <dig> and aging-regulated genes that are independent of hs was then determined by network generation .
interestingly, the interaction network of aging-associated genes regulated by hsf- <dig> independently of hs is four-fold larger than the network of aging genes that depend on hs.
we thus conclude that hsf- <dig> may have a role in impacting longevity that can be separated from its role in stress responses.
hsf- <dig> regulates collagen genes which may affect the aging process
it is interesting that cuticle structure genes constitute the largest overlap with aging-related genes.
in humans, mutations in collagens lead to a large number of heritable human diseases such as osteoporosis and musculoskeletal diseases  <cit> .
collagens are long-lived proteins known to accumulate damage during aging, leading to a decline in tissue health  <cit> .
also, type i collagens become resistant to proteolysis upon age  <cit> , affecting their turnover.
interestingly, mice expressing cleavage-resistant type i collagen go through an accelerated aging process  <cit> .
thus, cellular aging can be affected by the state of the extracellular matrix in mammals.
recently, collagen production and extracellular matrix remodeling were determined to be essential for longevity in c. elegans.
collagen may directly affect signaling processes associated with longevity in c. elegans, including signaling through skn- <dig>  <cit> .
we note that hsf- <dig> was also recently shown to regulate cytoskeletal integrity in a process that can influence stress resistance and longevity in c. elegans  <cit> .
thus, the linkage of both the extracellular matrix and the cytoskeleton to hsf- <dig> may provide a mechanism by which hsf- <dig> promotes longevity.
CONCLUSIONS
next generation sequencing has allowed us to uncover highly varied roles for c. elegans hsf- <dig> in both hs-dependent and -independent mechanisms, including roles in the regulation of development, cytoprotection, metabolism, and aging .
network analyses show that under hs conditions, the nuclear hormone receptor nhr- <dig> may allow coordination of the hsf- <dig> response across tissues, while under basal conditions, the egf receptor let- <dig> may regulate a similar coordination.
these findings warrant further studies in order to further understand the methods of cell non-autonomous signaling across tissues.
a striking result shown here is that multiple genes involved in cuticle structure, including collagen genes, are enriched as hsf- <dig> targets in hs-dependent and -independent manners.
as recent studies link collagen to cytoprotection and longevity, the regulation of collagen expression may be one method by which hsf- <dig> enhances lifespan.
harnessing the ability of hsf- <dig> to regulate collagen could thus have broad appeal in the treatment of diseases of aging.

 when organisms are exposed to protein-denaturing stressors such as heat, the heat shock response is engaged to manage protein damage and restore proteostasis. the hsr is highly conserved across species and is regulated by the transcription factor heat shock factor. during basal conditions, hsf exists as a monomer in the cytoplasm and nucleus, and during stress conditions undergoes trimerization and accumulation in the nucleus, where it binds to heat shock elements in the promoters of heat shock protein genes. hsps primarily act as molecular chaperones which refold the misfolded proteins that accumulate during stress, but they can also have essential functions in protein synthesis, processing, and degradation. thus the hsr, and hsps, play a large role in maintaining organismal proteostasis. the soil-dwelling, free-living, nematode caenorhabditis elegans is a powerful model organism that has provided insights into the regulation of a number of stress response pathways, including the hsr. hsf- the c. elegans homolog to mammalian hsf contains conserved n-terminal dna-binding and trimerization domains, as well as a putative transactivation domain at the c-terminus. it has recently been shown that the same activity steps required for mammalian hsf activation, including trimerization, hyperphosphorylation, and induction of dna-binding, are also required for worm hsf- activation. studies in c. elegans show that hsf- plays a central role not only in the hsr, but also in contributing to organismal physiology. hsf- is essential to worm viability, as a truncated mutant that lacks the c-terminal putative activation domain is defective in chaperone induction and egg laying, and also has a decreased lifespan. in addition, this strain has a temperature-sensitive developmental arrest phenotype, with arrest occurring at the l2-l transition. various experiments using hsf- rna interference have shown that hsf- regulates the expression of specific hsp genes upon heat shock, and have also implicated a non-stress-induced role for hsf- in processes including development, metabolism, and longevity. interestingly, studies in c. elegans have identified the hsr as a cell non-autonomous process that requires thermosensory neurons for hsp induction. upon the completion of sequencing of the c. elegans genome, over 40 % of the predicted protein products were found to be significantly conserved in other organisms, and many signaling pathways are conserved. c. elegans is thus an excellent model system for studying the role of hsf- in stress responses and other physiological processes in a simple multicellular organism. in this study, we have performed rna-sequencing with synchronous larval stage l wild-type c. elegans fed empty vector control rnai or hsf- rnai treated with or without hs. we show that significant numbers of genes are upregulated as well as downregulated by hsf- under both conditions. in addition to hsp genes, hsf- is required for the regulation of genes involved in a wide variety of cellular processes including cytoprotection, development, metabolism, and aging. network analysis points to possible routes by which hsf- signaling may be coordinated across tissues. a nuclear hormone receptor may coordinate the hs-induced hsf- transcriptional response, while an epidermal growth factor receptor may coordinate the hs-independent response. surprisingly, the top hsf-1-regulated gene category, both with and without heat stress, is cuticle structure. this result, together with other recent studies, thus links regulation of the extracellular matrix to hsf- cytoprotection, and longevity.  experimental set-up for genome-wide analysis of regulation of gene expression by hsf-1 previous experiments have shown that hsf- regulates the expression of specific hsp genes upon hs, and have also implicated a non-stress-induced role for hsf- in development, metabolism, and longevity. to examine hs-dependent vs. -independent gene regulation by hsf- on a genome-wide level, we used whole transcriptome rna-sequencing. we treated synchronous l larval stage nematodes with rnai against hsf- or with an ev control plasmid until the l larval stage. at the l stage, we then treated nematodes from both groups with or without a 30 min 33 °c hs, as diagrammed. experiments were performed in biological duplicates. the l stage was chosen for our studies as this is a time when the response to hs is strong, prior to a sharp decline that occurs shortly after the transition to adulthood. these treatment conditions, optimized for our studies, resulted in a ~9- log2-fold induction of the hsp- gene c12c, a classical hsf- target gene, in hsf- animals treated with hs. as expected, rnai against hsf- blunted hsp- induction by hs. the efficiency of our rnai feeding strategy was assessed by testing the effects of hsf- rnai on transcription driven by two heat shock protein promoter- gfp reporter worm strains. hs increases gfp expression, and this effect is dependent on hsf- as demonstrated with hsf- rnai. using an hsf-1::gfp overexpression worm strain, we also show that hsf- protein levels are reduced 80 % in response to hsf- rnai treatment. overall, these data validate our hs treatment conditions and rnai feeding strategy. cluster analysis performed on biological replicate rna-seq samples revealed conserved patterns of expression induced by each treatment condition. we normalized each condition to the hsf-1;-hs control in order to determine fold changes in relative rna abundance. a complete list of the significant genes altered in response to each condition, after normalization to the control, is also provided. volcano plot analyses show that while a limited group of genes for each comparison have a log2-fold change of or higher, the majority of genes have a log -fold change of approximately or less. as growth temperature and hsf- expression levels can affect the rate of development in the worm, we verified that our observed gene expression changes were not simply due to a change in the rate of development between each treatment condition. to do this, we analyzed several genes that are known to be differentially expressed during development and molting, including abu- wrt- his- lin- abu- abu pqn- pin- ptr- abu- abu- and sdz-, and detected no significant expression differences in these genes across treatment groups. overall, our data indicate that the worms in our four treatment conditions are developmentally synchronous to one another, and that the biological replicates for each condition share a similar expression profile, thus validating our experimental conditions. next, to visualize total hs-dependent vs. -independent gene expression regulated by hsf- we constructed a venn diagram with the differentially expressed genes for each condition which were determined to be statistically significant as compared to the hsf-1;-hs control. the shaded areas of the venn diagram correspond to hs-dependent and -independent processes regulated by hsf-, and these are the transcripts that we have focused our subsequent analyses on. altogether, we found that genes are significantly regulated by hsf- during hs, and that genes are significantly regulated by hsf- independently of hs, highlighting that hsf- regulates both hs-dependent and -independent transcriptional processes. interestingly, only genes are significantly regulated by hs independently of hsf- hsf- is thus not only an essential transcriptional regulator for a majority of the genes altered by hs, but global rna expression analysis supports a gene-regulatory role for hsf- under both heat stress and non-stress conditions. a greater number of gene changes that depend on hsf- are independent of heat stress, thus highlighting the important role of hsf- in regulating gene expression under non-stress conditions. genes that are regulated by hsf- in response to hs genes that are normally upregulated by hsf- in response to hs to determine whether hsf- can affect gene expression in both a positive and negative fashion, we separated out the positively vs. negatively regulated genes and analyzed them by venn diagram. we find that transcripts are normally upregulated by hsf- upon hs. we next examined these genes in more depth. the top genes in this category are listed in table . included in the top upregulated transcripts are hsp- family genes and hsp- family genes, all with log2-fold changes greater than the presence of chaperone genes in our top hits was expected, and gave us confidence in our experimental strategy. aside from chaperone genes, there are a number of non-chaperones included in the top most upregulated genes, including the nucleosome remodeling factor complex member nurf-, the predicted collagen gene col- and various genes of unknown function. therefore, the top genes regulated by hsf- under hs conditions include hsp genes and genes with diverse functions.fig. genes that are normally upregulated by hsf- in response to hs. a the venn diagram shows the overlap among genes that were found to be significantly upregulated for each of the indicated comparisons between samples. the dark blue shaded area includes genes that are normally upregulated by hsf- upon hs. the q-value is the fdr-adjusted p-value of the test statistic, as determined by the benjamini-hochberg correction for multiple testing. b hierarchical clustering of the genes normally upregulated by hsf- upon hs. lane corresponds to the fold change of the genes found in the dark blue section of the venn diagram in in the hsf-1;+hs vs. control samples. as a comparison, lane corresponds to the fold change of the same genes found in lane but in the hsf-1;+hs vs. control samples, as determined by rna-seq. the heat map was organized using cluster by k-means and euclidean distance. c top processes normally upregulated by hsf- during hs. the genes found in the dark blue section of the venn diagram in were classified by gene ontology terms that were determined using david f44e f44e f44e f44e y46h3a.3 hsp- y46h3a.2 hsp- t27e hsp- c12c hsp-70 t27e hsp- t27e hsp- y38e10a.13 nspe-1 t27e hsp- f26h nurf-1 zc zc d scp-1 r r b col-149 the transcript id, gene name, fold change as compared to the hsf-1;-hs control, and description as provided from wormbase, are listed for the genes with the highest positive fold changes in expression. a complete list of significantly upregulated transcripts is given we then further examined the induction characteristics of the top hsf-1-dependent genes induced by hs. the log2-fold changes for a subset of these genes are plotted and compared to the expression of the same genes in the presence of hs but in the absence of hsf-. the fact that hsf- rnai completely eliminates hs-inducibility of these genes highlights their dependency on hsf- independent quantitative rt-pcr for the same subset of highly induced genes validates our rna-seq data. in order to better visualize the global patterns of transcript upregulation by hsf- in response to hs, we constructed a heat map of the significantly upregulated genes. interestingly, and consistent with the data for a set of the top upregulated genes, genes that are normally upregulated by hsf- upon hs are either unchanged or downregulated under hs conditions upon hsf- knockdown on a global level. the fact that many of the hs-induced genes that require hsf- are downregulated upon hsf- knockdown implies that hsf- may play a role in the basal regulation of these genes, which is then enhanced upon hs. together, these data demonstrate the hsf- dependency of most hs-induced genes. to identify the various functional processes normally upregulated by hsf- during hs, we used the database for annotation, visualization, and integrated discovery classification tool to define the top gene ontology terms for all of the genes found to be significantly upregulated. the complete output from david is also provided. surprisingly, the top functional category, with an enrichment score of contains genes involved in cuticle structure. the next four categories, all with enrichment scores under include genes involved in translation, the response to stress, the regulation of growth, and amine catabolic processes. we thus find that the largest functional category of genes regulated by hs is not the expected heat stress-responsive gene-set, but instead genes associated with forming cuticle structure. we next tested the effects of a cuticle collagen gene, col- on induction of the hsr by measuring hsp- promoter activity in phsp-70::gfp worms. we see that col- rnai decreases hs-induced hsp- promoter activity, and may control tissue-specific regulation of the hsr. testing the effects of other collagen genes on regulation of the hsr may provide insight into a signaling role for collagens in coordinating stress responses. genes that are normally downregulated by hsf- in response to hs we next examined the genes separated out from the venn diagram analysis to be normally downregulated by hsf- upon hs. we find that there are transcripts in this group. the top genes normally downregulated by hsf- upon hs are listed in table . there are a variety of distinct transcripts downregulated by hsf- during hs. the gene with the largest log2-fold decrease is acs- which encodes an acyl-coa synthetase. this enzyme participates in breakdown of fatty acids into acyl-coa in the mitochondria to allow for β-oxidation, thus increasing fat consumption. another downregulated gene is dct- which encodes a protein that has pro-apoptotic activity. the tetraspanin family member tsp- is also downregulated. the tetraspanin family of proteins is required for epithelial integrity in the worm and regulates cuticle formation. other downregulated genes include fbxa- and fbxa- which encode fboxa proteins with unknown functions; nep- which encodes a zinc metallopeptidase that negatively regulates signaling peptides; glc- which encodes a subunit of a glutamate-gated chloride channel; and delm- which encodes an ortholog of an acid-sensing ion channel family member. there are also multiple transcripts of unknown function in this gene group. therefore, the top genes normally downregulated by hsf- under hs conditions have a diverse set of functions.fig. genes that are normally downregulated by hsf- in response to hs. a the venn diagram shows the overlap among genes that were found to be significantly downregulated for each of the indicated comparisons between samples. the dark purple shaded area includes genes that are normally downregulated by hsf- upon hs. the q-value is the fdr-adjusted p-value of the test statistic, as determined by the benjamini-hochberg correction for multiple testing. b hierarchical clustering of the genes normally downregulated by hsf- upon hs. lane corresponds to the fold change of the genes found in the dark purple section of the venn diagram in in the hsf-1;+hs vs. control samples. as a comparison, lane corresponds to the fold change of the same genes found in lane but in the hsf-1;+hs vs control samples, as determined by rna-seq. the heat map was organized using cluster by k-means and euclidean distance. c top processes normally downregulated by hsf- during hs. the genes found in the dark purple section of the venn diagram in were classified by gene ontology terms that were determined using david f28f acs-2 w09g w09g c07a c07a c14f dct-1 c02f tsp-1 y54f10bm.11 fbxa-66 y119d3b.9 fbxa-21 k08d k08d c49g c49g t12a t12a f33h f33h y47h10a.5 y47h10a.5 zk nep-26 f11a glc-1 c24g delm-2 the transcript id, gene name, fold change as compared to the hsf-1;-hs control, and description as provided from wormbase are listed for the genes with the highest negative fold changes in expression. a complete list of significantly downregulated transcripts is given we then further studied the top genes that are normally downregulated by hsf- upon hs. the log2-fold changes of a subset of the top hsf-1-dependent genes repressed by hs are plotted, and these data are compared to the expression of the same genes in the presence of hs but in the absence of hsf-. interestingly, we found that all of the genes that are downregulated by hs in the presence of hsf- are upregulated by hs in the absence of hsf- one way this could occur is if hsf- normally suppresses the expression of these genes, and hs-activated hsf- suppresses them even further. to verify our rna-seq data, we performed independent qrt-pcr for the same subset of highly downregulated genes, and found that the qrt-pcr data was consistent with our rna-seq data. to visualize the patterns of transcripts that are normally downregulated by hsf- upon hs, we constructed a heat map to visualize the log2-fold changes of the significantly downregulated genes. as a comparison, the expression of the same transcripts under hs conditions upon hsf- knockdown is shown. as with the data for the top downregulated genes, many of the genes that are normally downregulated by hsf- under hs conditions are conversely upregulated by hs in the absence of hsf- thus, hs can have completely opposite effects on gene expression depending on the presence or absence of hsf- upon david analysis of gene ontology terms for the repressed genes, the top functional categories all had enrichment scores of or lower. these functional categories include genes that encode proteins with kinase activity, ion binding activity, transcription, atp-binding activity, and reproductive development. the complete output from david is also provided. overall, these results show that a diverse group of genes are normally suppressed by hsf- during hs. genes that are regulated by hsf- independently of hs genes that are normally upregulated by hsf- independently of hs while hsf- has been historically studied for its role in regulating responses elicited by hs, hsf- also has functions that are independent of hs including roles in development, metabolism, and longevity. to identify processes upregulated by hsf- independently of hs, we examined the genes from the venn diagram that we determined to be downregulated in response to hsf- rnai independently of hs, suggesting that they are normally upregulated by hsf-. in order to gain insight into the normal hsf-1-regulatory role of these hs-independent genes, we reversed our data comparison to obtain the fold change, as this gene group is shown to be downregulated in response to hsf- rnai and would thus normally be upregulated by hsf- fig. genes that are normally upregulated by hsf- independently of hs. a the venn diagram shows the overlap among genes that were found to be significantly downregulated for each of the indicated comparisons between samples. the light purple shaded area includes genes that are downregulated upon treatment with hsf- rnai, and are likely normally induced by hsf- independently of heat shock, therefore are referred to as upregulated genes. the q-value is the fdr-adjusted p-value of the test statistic, as determined by the benjamini-hochberg correction for multiple testing. b hierarchical clustering of the genes normally upregulated by hsf- independently of hs. the fold change of genes found in the light purple section of the venn diagram in were determined by rna-seq to be downregulated in response to hsf- rnai, and would thus normally be upregulated by hsf- lane corresponds to the fold change of these genes in the control vs. hsf-1;-hs samples, and as a comparison, lane corresponds to each the fold change of the same genes found in lane but in the control vs. hsf-1;+hs samples. the heat map was organized using cluster by k-means and euclidean distance. c top processes normally upregulated by hsf- independently of hs. the genes found in the light purple section of the venn diagram were classified by gene ontology terms that were determined using david the top genes that are normally upregulated by hsf- under non-stress conditions are listed in table . surprisingly, a group of vitellogenin lipid transporter transcripts are among the top genes. vitellogenins are made in the intestine of late larval/early adult hermaphrodites and are taken up by the germ cells to provide nourishment to embryos. other top upregulated genes include acdh- which encodes a short chain acyl-coa dehydrogenase and may play a role in energy production; k11g, which is predicted to be an ortholog of human butyrylcholinesterase; folt- which encodes a folate transporter; ilys- which is predicted to have lysozyme activity; zc, which is predicted to have g-protein coupled receptor activity; fat- which encodes a fatty acid desaturase; k10b, which is predicted to have carboxypeptidase activity; y52e8a. which encodes the ortholog to a major facilitator superfamily; ugt- which encodes the ortholog of a polypeptide predicted to have transferase activity; and two genes with unknown function. therefore, a diverse set of genes, including vitellogenins and others, are normally upregulated by hsf- independently of hs.table top genes normally upregulated by hsf- independently of hs c55b acdh-1 f59d vit-3 f59d vit-4 c04f vit-5 k09f vit-1 y40h7a.10 y40h7a.10 k11g k11g f37b folt-2 f22a ilys-5 zc zc f10d fat-7 k10b k10b y52e8a.4 y52e8a.4 c08f ugt-22 f54f f54f the transcript id, gene name, and fold change in gene expression in the comparison of the control vs. hsf-1;-hs are listed for the top genes normally upregulated by hsf- independently of hs. gene descriptions, as provided from wormbase, are also listed. a complete list of the significantly altered transcripts is given we then further characterized the induction characteristics of the top genes that are normally upregulated by hsf- independently of heat stress. the log2-fold changes of a subset of these top genes are plotted, and are compared to the expression of the same genes in the presence of hs and absence of hsf-. this data shows that hs does not affect the expression of these genes in the absence of hsf- the expression of these mrnas was also verified with qrt-pcr, and the results are consistent with the rna-seq data. to investigate a hs-independent role for hsf- in the induction of gene expression on a global level, we generated a heat map of all genes found via venn diagram to be normally upregulated by hsf- in the absence of hs. as a comparison, genes that are normally upregulated by hsf- in the presence of hs are plotted. the transcripts in this group that are normally upregulated by hsf- in the absence of hs remain upregulated or unchanged in the presence of hs, verifying the heat stress-independent induction of this gene group. we next used david to determine the top functional processes that are normally upregulated by hsf- independently of hs. we found that cuticle structure was again the gene category with the highest enrichment score, as was also the case for the genes that are upregulated by hsf- during hs. this indicates that hsf- may regulate the basal expression of genes involved in cuticle structure, and that these genes are then further induced upon hs. other functional processes, with enrichment scores less than include genes that encode proteins involved in the mitochondrial envelope, acyl-coa dehydrogenase activity, peptidase activity, and oxidoreductase activity. the complete output from david is also available. the mitochondrial envelope, acyl-coa dehydrogenase activity, peptidase activity, and oxidoreductase activity are all processes that can be linked to metabolism, further substantiating a functional role for hsf- in regulating this process. genes that are normally downregulated by hsf- independently of hs we next examined the genes from the venn diagram that we determined to be upregulated in response to hsf- rnai independently of hs, suggesting that they are normally downregulated by hsf-. we reversed our data comparison to obtain the fold change, as this gene group is shown to be upregulated in response to hsf- rnai and would thus normally be downregulated by hsf- the top genes in this category are listed in table . there are a variety of transcript types in this list, including t22f, which is an mrna that encodes the ortholog of the human solute carrier family 17; eol- which regulates olfactory learning; bo, which encodes an ortholog of human lipopolysaccharide-induced tnf factor; col- which encodes a structural constituent of the cuticle; fbxa- and t08e, which encode proteins that contain f-box motifs predicted to be important for protein-protein interactions; clec- and clec- which encode carbohydrate binding proteins; srg- which encodes a protein involved in embryo development; clec- which encodes a protein involved in the immune response; b, which encodes an ortholog of human cingulin-like 1; clec- which is predicted to have carbohydrate binding activity; f22f, which encodes an ortholog of human grb interacting gyf protein 2; and y47h10a. and zk, which both have unknown functions. overall, we find that a diverse set of mrnas are normally downregulated by hsf- independently of hs, indicating that hsf- may normally suppress a variety of cellular processes in a hs-independent manner.fig. genes that are normally downregulated by hsf- independently of hs. a the venn diagram shows the overlap among genes that were found to be significantly upregulated for each of the indicated comparisons between samples. the light blue shaded area includes genes that are upregulated upon treatment with hsf- rnai, and are likely normally suppressed by hsf- independently of heat shock, therefore are referred to as downregulated genes. the q-value is the fdr-adjusted p-value of the test statistic, as determined by the benjamini-hochberg correction for multiple testing. b hierarchical clustering comparing the genes normally suppressed by hsf- independently of hs. the fold change of genes found in the light blue section of the venn diagram in were determined by rna-seq to be upregulated in response to hsf- rnai, and would thus normally be suppressed by hsf- lane corresponds to the fold change of these genes in the control vs. hsf-1;-hs samples, and as a comparison, lane corresponds to each the fold change of the same genes found in lane but in the control vs. hsf-1;+hs samples. the heat map was organized using cluster by k-means and euclidean distance. c top processes normally downregulated by hsf- independently of hs. the genes found in the light blue section of the venn diagram were classified by gene ontology terms that were determined using david t22f t22f t26f eol-1 b b y47h10a.5 y47h10a.5 d col-158 c08e fbxa-163 f07e f07e y46c8al.2 clec-174 t07h srg-31 zk clec-60 b b zk zk h16d clec-13 t08e t08e f22g f22g the transcript id, gene name, and fold change in gene expression in the comparison of the control vs hsf-1;-hs are listed for the top genes normally downregulated by hsf- independently of hs. gene descriptions, as provided from wormbase, are also listed. a complete list of the significantly altered transcripts is given the induction characteristics of the top genes in this category were then analyzed. the log2-fold changes from the rna-seq data for a subset these genes are plotted, and are compared to the expression of the same genes in the presence of hs in the absence of hsf-. the expression of these mrnas was also verified with qrt-pcr, and the results are consistent with the rna-seq data. altogether, these data confirm that hs does not affect the expression of these genes in the absence of hsf- to investigate a hs-independent role for hsf- in the suppression of gene expression, we constructed a heat map of all genes found via venn diagram to be normally suppressed by hsf- in the absence of hs. as a comparison, the expression patterns of the same transcripts suppressed by hsf- in the presence of hs are shown. the transcripts in this group that are significantly downregulated by hsf- in the absence of hs remain downregulated or unchanged by hsf- in the presence of hs, further verifying that regulation of this subset of genes by hsf- is independent of hs. we next used david to determine the functional processes that are normally downregulated by hsf- independently of hs. genes involved in cell cycle processes were most abundant, with an enrichment score of followed by genes involved in epithelium development, regulation of growth, genitalia development, and cell migration, all with enrichment scores under. the complete output from david is also available. cell cycle processes, epithelium development, regulation of growth, genitalia development, and cell migration are all processes that can be linked to development, thus confirming a hs-independent role for hsf- in development. discussion regulation of gene expression by hsf-1 c. elegans is a useful model organism for identifying regulatory processes that are shared between species. while the transcription factor hsf- has classically been studied as a factor that is responsive to cytoplasmic proteotoxic stress, it is becoming increasingly evident that this transcription factor also has major non-stress-induced roles in coordinating gene expression. with the rna-sequencing experiments performed here, we confirm that hsf- can regulate gene expression under both heat stress and non-stress conditions. in addition to genes that are classically stress-responsive, such as chaperones, our work shows that hsf- also regulates sets of genes involved in a variety of cellular processes including metabolism, development, and longevity. cuticle structure genes are normally upregulated by hsf- via hs-dependent and -independent mechanisms a surprising result of our study is that genes controlling cuticle structure comprise the largest gene ontology group that is upregulated by hsf- in both a hs-dependent and -independent manner. the c. elegans cuticle is an exoskeletal structure that creates a barrier between the animal and the environment, provides body shape, and allows movement via attachment to muscle. many of the genes in the cuticle structure category are collagens, structural proteins that form an extracellular matrix composing the exoskeleton, or cuticle, of the nematode. there are ~ distinct collagen genes in c. elegans, and they are expressed in a tissue-specific fashion and at distinct temporal times. cuticle structure is controlled by enzymes involved in collagen processing, and the polymerization pattern is dictated by actin filaments that are organized in specific patterns around the body of the worm. in humans, collagens comprise about one-third of all expressed protein. aside from the structural role of collagens, these genes can also participate in signal transduction. collagen genes were recently found to be upregulated by skn- the c. elegans oxidative stress-responsive transcription factor. in future work, it will be interesting to test whether collagen can act to relay signals to stress-specific transcription factors including skn- and hsf- roles for hsf- in regulating metabolism and development in a hs-independent manner although hsf- has classically been studied as a transcription factor that responds to hs and cytoplasmic proteotoxic stress, hsf- has recently been gaining importance as a transcription factor that is involved in non-stress processes including development and metabolism. in mice, hsf family members have been documented to be involved in diverse developmental processes, including oogenesis, spermatogenesis, and corticogenesis. hsf- in the worm has also been shown to be regulated by insulin/igf- tgf-β, and cgmp signaling to control development. the finding that mammalian hsf can be regulated by sirt a deacetylase that is under metabolic control, provides evidence that hsf- and metabolism are linked. this finding is also true for c. elegans hsf- as the sirt homolog sir- regulates the c. elegans hsr. additionally, the insulin-like signaling regulators ddl-1/ have been linked to hsf- regulation. here, we show that under non-stress conditions, hsf- regulates a number of genes involved in developmental and metabolic processes. therefore, our work further highlights the links between hsf- and these non-stress processes. network analysis identifies a nuclear hormone receptor as a common link between processes regulated by hsf- upon hs to determine how the genes regulated by hsf- during hs may interact with each other, we performed network analysis using genes associated with the top go-terms as determined by david. we used the mimi plugin to integrate data from protein interaction databases to allow for the creation of interaction networks using the network-building software cytoscape. this analysis enabled us to identify interacting partners shared by at least two genes regulated by hsf- during hs. the transcripts induced by hsf- during hs are shown in red, while the transcripts downregulated by hsf- during hs are shown in blue, with the intensity of color correlating to the fold change. genes that are not colored were not found to be affected by hsf- during hs in our dataset, but are neighbors shared by at least two genes that were affected. we found network linkages between the processes of cuticle structure formation, translation, the response to stress, protein kinase activity, and transcription. interestingly, the nuclear hormone receptor nhr- is a common link between several of the hs-regulated processes that require hsf- including cuticle structure, translation, and the response to stress. nuclear hormone receptors comprise a class of ligand-gated transcription factors that bind to small molecule metabolites such as fatty acids, vitamins, and steroids to directly regulate gene transcription. they are thus well-poised to coordinate metabolism, development, reproduction, and homeostasis across diverse tissues. nhr- is broadly expressed in c. elegans and is located in eight head neurons, the sensory pvd neurons in the posterior lateral body wall, the pharynx, the intestine, the dorsal peri-vulva region, and the somatic gonad precursor cells. in future work, it will be interesting to test the role of nhr- and other nuclear hormone receptors in the hsr, and to see if it can contribute towards the coordination of this response across tissues.fig. network analyses of the top hsf-1-regulated processes. a predicted network regulated by hsf- during hs. genes associated with the top induced and suppressed processes in figs. 1c and 2c were used for analysis. b predicted network regulated by hsf- independently of hs. genes associated with the top induced and suppressed processes in figs. 3c and 4c were used for analysis. for a and b, the color of each gene corresponds to the degree of hsf- regulation of the corresponding transcript. network analysis was done with mimi using the cytoscape platform. the uncolored genes were not affected by hsf- during or independently of hs in our dataset, but are neighbors shared by at least two genes that were affected in our dataset network analysis identifies a tyrosine kinase as a common link between various developmental processes regulated by hsf- independently of hs to uncover c. elegans interaction networks associated with processes regulated by hsf- independently of hs, we performed network analysis using genes associated with the top go-terms as determined by david. network linkages were found for genes involved in the mitochondrial envelope, peptidase activity, oxidoreductase activity, cell cycle processes, and epithelium development. we found that let- an epidermal growth factor receptor tyrosine kinase, is predicted to interact with many of these transcripts. the egf pathway in c. elegans has been linked to multiple developmental pathways. this rtk may thus allow for signaling to hsf- during non-stress conditions to modulate developmental gene expression. interestingly, hsf null mouse embryonic fibroblasts are defective in both basal and egf-induced cell migration, so the link between hsf- and the egf signaling pathways may be conserved across species. it will thus be worthwhile in future work to test for the involvement of let- in the regulation of hsf- activity in c. elegans. hsf- impacts aging-regulated gene expression as hsf- has been implicated to play an important role in both aging and disease, we analyzed the role of hsf- in regulating age-associated transcriptional changes in our data-sets. by comparing the transcriptome profiles between young and old adult c. elegans, a previous study by budovskaya et al. identified genes to be differentially regulated upon worm aging. a venn diagram comparison of these age-regulated genes with those that we found to be regulated by hsf- during hs shows that aging-associated genes overlapped with our dataset. a complete list of genes shared between both data-sets is also provided. the functional processes regulated by this overlapping gene set were then determined via david analysis. cuticle structure was the largest functional category, with an enrichment score of. other gene categories, all with enrichment scores of or lower, include cuticle development, the response to stress, amine catabolic processes, carbohydrate binding, and membrane structure. network analysis performed on the overlapping genes shows that only a small subset of these genes are predicted to interact with each other.fig. age-regulated genes controlled by hsf- a the venn diagram shows the overlap among genes that are differentially expressed during aging and regulated by hsf- during hs. the venn diagram was made using genes previously found to be regulated during aging by budovskaya et al. compared to genes we found to be regulated by hsf- during hs. b cellular processes affected by aging and hsf- during hs. genes shared between the aging dataset and hsf-1-regulated hs-dependent dataset from were analyzed with david and the gene ontology terms are listed in order of decreasing enrichment. c network analysis of the genes regulated by aging and hsf- during hs. network analysis was done with mimi using the cytoscape platform and the transcripts shared between data-sets. the color of each transcript corresponds to the degree of hsf- regulation. genes that are not colored were not affected by hsf- our dataset, but are neighbors shared by at least two genes that were affected in our dataset. d the venn diagram shows the overlap among genes that are differentially expressed during aging and regulated by hsf- independently of hs. the venn diagram was made using genes previously found to be regulated during aging by budovskaya et al. compared to genes we found to be regulated by hsf- independently of hs. e cellular processes affected by aging and hsf- independently of hs. genes shared between the aging dataset and hsf-1-regulated hs-independent dataset from were analyzed with david and the gene ontology terms are listed in order of decreasing enrichment. f network analysis of the genes regulated by aging and hsf- independently of hs. network analysis was done with mimi using the cytoscape platform and the transcripts shared between data-sets. the color of each transcript corresponds to the degree of hsf- regulation. genes that are not colored were not affected by hsf- in our dataset, but are neighbors shared by at least two genes that were affected in our dataset next, a comparison between aging-associated genes and those we found to be regulated by hsf- independently of hs was done. a venn diagram shows that aging-associated genes overlapped with our dataset. a complete list of genes shared between both data-sets is also provided. the functional processes regulated by this gene set was then determined via david analysis. cuticle structure was again the largest category, with an enrichment score of the other categories, with enrichment scores of or lower, include peptidase activity, c-type lectin, vitamin binding, and lifespan-associated processes. the transcriptional impact of these hsf- and aging-regulated genes that are independent of hs was then determined by network generation. interestingly, the interaction network of aging-associated genes regulated by hsf- independently of hs is four-fold larger than the network of aging genes that depend on hs. we thus conclude that hsf- may have a role in impacting longevity that can be separated from its role in stress responses. hsf- regulates collagen genes which may affect the aging process it is interesting that cuticle structure genes constitute the largest overlap with aging-related genes. in humans, mutations in collagens lead to a large number of heritable human diseases such as osteoporosis and musculoskeletal diseases. collagens are long-lived proteins known to accumulate damage during aging, leading to a decline in tissue health. also, type i collagens become resistant to proteolysis upon age, affecting their turnover. interestingly, mice expressing cleavage-resistant type i collagen go through an accelerated aging process. thus, cellular aging can be affected by the state of the extracellular matrix in mammals. recently, collagen production and extracellular matrix remodeling were determined to be essential for longevity in c. elegans. collagen may directly affect signaling processes associated with longevity in c. elegans, including signaling through skn-. we note that hsf- was also recently shown to regulate cytoskeletal integrity in a process that can influence stress resistance and longevity in c. elegans. thus, the linkage of both the extracellular matrix and the cytoskeleton to hsf- may provide a mechanism by which hsf- promotes longevity.  next generation sequencing has allowed us to uncover highly varied roles for c. elegans hsf- in both hs-dependent and -independent mechanisms, including roles in the regulation of development, cytoprotection, metabolism, and aging. network analyses show that under hs conditions, the nuclear hormone receptor nhr- may allow coordination of the hsf- response across tissues, while under basal conditions, the egf receptor let- may regulate a similar coordination. these findings warrant further studies in order to further understand the methods of cell non-autonomous signaling across tissues. a striking result shown here is that multiple genes involved in cuticle structure, including collagen genes, are enriched as hsf- targets in hs-dependent and -independent manners. as recent studies link collagen to cytoprotection and longevity, the regulation of collagen expression may be one method by which hsf- enhances lifespan. harnessing the ability of hsf- to regulate collagen could thus have broad appeal in the treatment of diseases of aging. 
almost all genes regulated by hs require hsf- reinforcing the central role of this transcription factor in the response to heat stress. surprisingly, the cellular process most highly regulated by hsf- both with and without heat stress, is cuticle structure. the findings that a nuclear hormone receptor may coordinate the hs-induced hsf- transcriptional response, while an epidermal growth factor receptor may coordinate the hs-independent response, indicate that these factors could promote cell non-autonomous signaling that occurs through hsf- finally, this work highlights the genes involved in cuticle structure as important hsf- targets that may play roles in promoting both cytoprotection as well as longevity. our results confirm that c. elegans hsf- can regulate gene expression in both a stress-dependent and -independent fashion. in c. elegans, the hsf homolog hsf- is an essential protein that is required to mount a stress-dependent response, as well as to coordinate various stress-independent processes including development, metabolism, and the regulation of lifespan. in this work, we have performed rna-sequencing for c. elegans cultured in the presence and absence of hsf- rnai followed by treatment with or without heat shock. hsf- therefore coordinates various physiological processes in c. elegans, and hsf- activity may be coordinated across tissues by nuclear hormone receptor and epidermal growth factor receptor signaling. this work provides genome-wide hsf- regulatory networks in c. elegans that are both heat stress-dependent and -independent. this response, driven by the heat shock transcription factor hsf restores proteostasis through the induction of molecular chaperones and other genes. the heat shock response, induced by cytoplasmic proteotoxic stress, is one of the most highly conserved transcriptional responses. this experimental design thus allows for the determination of both heat shock-dependent and -independent biological targets of hsf- on a genome-wide level. via network analyses, we identify a nuclear hormone receptor as a common link between genes that are regulated by hsf- in a hs-dependent manner, and an epidermal growth factor receptor as a common link between genes that are regulated by hsf- in a hs-independent manner. within both the heat stress-dependent and -independent gene groups, significant numbers of genes are upregulated as well as downregulated, demonstrating that hsf- can both activate and repress gene expression either directly or indirectly. we show that hsf- is responsible for regulating many genes outside of classical heat stress-responsive genes, including genes involved in development, metabolism, and aging.
 the heat shock response, induced by cytoplasmic proteotoxic stress, is one of the most highly conserved transcriptional responses. this response, driven by the heat shock transcription factor hsf restores proteostasis through the induction of molecular chaperones and other genes. in addition to stress-dependent functions, hsf has also been implicated in various stress-independent functions. in c. elegans, the hsf homolog hsf- is an essential protein that is required to mount a stress-dependent response, as well as to coordinate various stress-independent processes including development, metabolism, and the regulation of lifespan. in this work, we have performed rna-sequencing for c. elegans cultured in the presence and absence of hsf- rnai followed by treatment with or without heat shock. this experimental design thus allows for the determination of both heat shock-dependent and -independent biological targets of hsf- on a genome-wide level.  our results confirm that c. elegans hsf- can regulate gene expression in both a stress-dependent and -independent fashion. almost all genes regulated by hs require hsf- reinforcing the central role of this transcription factor in the response to heat stress. as expected, major categories of hsf-1-regulated genes include cytoprotection, development, metabolism, and aging. within both the heat stress-dependent and -independent gene groups, significant numbers of genes are upregulated as well as downregulated, demonstrating that hsf- can both activate and repress gene expression either directly or indirectly. surprisingly, the cellular process most highly regulated by hsf- both with and without heat stress, is cuticle structure. via network analyses, we identify a nuclear hormone receptor as a common link between genes that are regulated by hsf- in a hs-dependent manner, and an epidermal growth factor receptor as a common link between genes that are regulated by hsf- in a hs-independent manner. hsf- therefore coordinates various physiological processes in c. elegans, and hsf- activity may be coordinated across tissues by nuclear hormone receptor and epidermal growth factor receptor signaling.  this work provides genome-wide hsf- regulatory networks in c. elegans that are both heat stress-dependent and -independent. we show that hsf- is responsible for regulating many genes outside of classical heat stress-responsive genes, including genes involved in development, metabolism, and aging. the findings that a nuclear hormone receptor may coordinate the hs-induced hsf- transcriptional response, while an epidermal growth factor receptor may coordinate the hs-independent response, indicate that these factors could promote cell non-autonomous signaling that occurs through hsf- finally, this work highlights the genes involved in cuticle structure as important hsf- targets that may play roles in promoting both cytoprotection as well as longevity. electronic supplementary material the online version of this article contains supplementary material, which is available to authorized users. keywords rna-seqheat shock responsestressc. eleganstranscript analysishsf-1http://dx.doi.org/http://dx.doi.org/ /100008900university of south floridaissue-copyright-statement© the author 2016 