Question: What is the role of Caenorhabditis elegans Heterochromatin protein 1 (HPL-2) in development?

Context:
Caenorhabditis elegans Heterochromatin protein 1 (HPL-2) links developmental plasticity, longevity and lipid metabolism.
 We show that HPL-2 regulates the expression of germline genes, extracellular matrix components and genes involved in lipid metabolism. Comparison of our expression data with HPL-2 ChIP-on-chip profiles reveals that a significant number of genes up- and down-regulated in the absence of HPL-2 are bound by HPL-2. Germline genes are specifically up-regulated in hpl-2 mutants, consistent with the function of HPL-2 as a repressor of ectopic germ cell fate. 
HPL-2 regulates the dauer developmental decision, a striking example of phenotypic plasticity in which environmental conditions determine developmental fate.
Our results suggest that the worm HP1 homologue HPL-2 may coordinately regulate dauer diapause, longevity and lipid metabolism, three processes dependent on developmental input and environmental conditions.
Interestingly, lin-61 genetically interacts with two other synMuvB genes, hpl-2, an HP1 homologous H3K9me2/3 binding factor, and met-2, a SETDB1 homologous H3K9 methyl transferase (H3K9MT), in determining C. elegans vulva development and fertility.
We have specifically characterized the intranuclear positioning of in vivo fluorescence of the Caenorhabditis elegans HP1 homologue HPL-2 as a marker for heterochromatin domains in developing embryos. 
While HPL-2 functions in vulval and germline development, no function has so far been attributed to HPL-1. Here we report the characterization of an hpl-1 null allele. We show that while the absence of hpl-1 alone results in no obvious phenotype, hpl-1;hpl-2 double mutants show synthetic, temperature sensitive phenotypes including larval lethality and severe defects in the development of the somatic gonad. Furthermore, we find that hpl-1 has an unexpected role in vulval development by acting redundantly with hpl-2, but not other genes previously implicated in vulval development. Localization studies show that like HPL-2, HPL-1 is a ubiquitously expressed nuclear protein. However, HPL-1 and HPL-2 localization does not completely overlap. Our results show that HPL-1 and HPL-2 play both unique and redundant functions in post-embryonic development.
We show that one of the homologues, HPL-2, is required for the formation of a functional germline and for the development of the vulva by acting in an Rb-related pathway. 
A heterochromatin protein 1 homologue in Caenorhabditis elegans acts in germline and vulval development.
We have specifically characterized the intranuclear positioning of in vivo fluorescence of the Caenorhabditis elegans HP1 homologue HPL-2 as a marker for heterochromatin domains in developing embryos.
Germline genes are specifically up-regulated in hpl-2 mutants, consistent with the function of HPL-2 as a repressor of ectopic germ cell fate.

Answer: Caenorhabditis elegans Heterochromatin protein 1 (HPL-2) links developmental plasticity, longevity and lipid metabolism. HPL-2 regulates the expression of germline genes, extracellular matrix components and genes involved in lipid metabolism. In addition, HPL-2 regulates the dauer developmental decision, a striking example of phenotypic plasticity in which environmental conditions determine developmental fate. Furthermore, it is required for the formation of a functional germline and for the development of the vulva by acting in an Rb-related pathway.