bluuebunny/crossref_metadata_2025 huggingface dataset:
Sex Determination in the Parasitic Nematode Strongyloides ratti
Authors: Harvey S C , Viney M E
Published: April 2021

The parasitic nematode Strongyloides ratti reproduces by both parthenogenesis and sexual reproduction, but its genetics are poorly understood. Cytological evidence suggests that sex determination is an XX/XO system. To investigate this genetically, we isolated a number of sex-linked DNA markers. One of these markers, Sr-mvP1, was shown to be single copy and present at a higher dose in free-living females than in free-living males. The inheritance of two alleles of Sr-mvP1 by RFLP analysis was consistent with XX female and XO male genotypes. Analysis of the results of sexual reproduction demonstrated that all progeny inherit the single paternal X chromosome and one of the two maternal X chromosomes. Therefore, all stages of the S. ratti life cycle, with the exception of the free-living males, are XX and genetically female. These findings are considered in relation to previous analyses of S. ratti and to other known sex determination systems.
A Genetic Screen for Suppressors and Enhancers of the Drosophila PAN GU Cell Cycle Kinase Identifies Cyclin B as a Target
Authors: Lee Laura A , Elfring Lisa K , Bosco Giovanni , Orr-Weaver Terry L
Published: April 2021

The early cell cycles of Drosophila embryogenesis involve rapid oscillations between S phase and mitosis. These unique S-M cycles are driven by maternal stockpiles of components necessary for DNA replication and mitosis. Three genes, pan gu (png), plutonium (plu), and giant nuclei (gnu) are required to control the cell cycle specifically at the onset of Drosophila development by inhibiting DNA replication and promoting mitosis. PNG is a protein kinase that is in a complex with PLU. We employed a sensitized png mutant phenotype to screen for genes that when reduced in dosage would dominantly suppress or enhance png. We screened deficiencies covering over 50% of the autosomes and identified both enhancers and suppressors. Mutations in eIF-5A and PP1 87B dominantly suppress png. Cyclin B was shown to be a key PNG target. Mutations in cyclin B dominantly enhance png, whereas png is suppressed by cyclin B overexpression. Suppression occurs via restoration of Cyclin B protein levels that are decreased in png mutants. The plu and gnu phenotypes are also suppressed by cyclin B overexpression. These studies demonstrate that a crucial function of PNG in controlling the cell cycle is to permit the accumulation of adequate levels of Cyclin B protein.
Molecular Genetic Dissection of the Sex-Specific and Vital Functions of the Drosophila melanogaster Sex Determination Gene fruitless
Authors: Anand Anuranjan , Villella Adriana , Ryner Lisa C , Carlo Troy , Goodwin Stephen F , Song Ho-Juhn , Gailey Donald A , Morales Ana , Hall Jeffrey C , Baker Bruce S , Taylor Barbara J
Published: April 2021

A multibranched hierarchy of regulatory genes controls all aspects of somatic sexual development in Drosophila melanogaster. One branch of this hierarchy is headed by the fruitless (fru) gene and functions in the central nervous system, where it is necessary for male courtship behavior as well as the differentiation of a male-specific abdominal structure, the muscle of Lawrence (MOL). A preliminary investigation of several of the mutations described here showed that the fru gene also has a sex-nonspecific vital function. The fru gene produces a complex set of transcripts through the use of four promoters and alternative splicing. Only the primary transcripts produced from the most distal (P1) promoter are sex-specifically spliced under direction of the sex-determination hierarchy. We have analyzed eight new fru mutations, created by X-ray mutagenesis and P-element excision, to try to gain insight into the relationship of specific transcript classes to specific fru functions. Males that lack the P1-derived fru transcripts show a complete absence of sexual behavior, but no other defects besides the loss of the MOL. Both males and females that have reduced levels of transcripts from the P3 promoter develop into adults but frequently die after failing to eclose. Analysis of the morphology and behavior of adult escapers showed that P3-encoded functions are required for the proper differentiation and eversion of imaginal discs. Furthermore, the reduction in the size of the neuromuscular junctions on abdominal muscles in these animals suggests that one of fru's sex-nonspecific functions involves general aspects of neuronal differentiation. In mutants that lack all fru transcripts as well as a small number of adjacent genes, animals die at an early pupal stage, indicating that fru's function is required only during late development. Thus, fru functions both in the sex-determination regulatory hierarchy to control male sexual behavior through sex-specific transcripts and sex-nonspecifically to control the development of imaginal discs and motorneuronal synapses during adult development through sex-nonspecific transcript classes.
Capture of DNA Sequences at Double-Strand Breaks in Mammalian Chromosomes
Authors: Lin Yunfu , Waldman Alan S
Published: April 2021

To study double-strand break (DSB)-induced mutations in mammalian chromosomes, we transfected thymidine kinase (tk)-deficient mouse fibroblasts with a DNA substrate containing a recognition site for yeast endonuclease I-SceI embedded within a functional tk gene. To introduce a genomic DSB, cells were electroporated with a plasmid expressing endonuclease I-SceI, and clones that had lost tk function were selected. Among 253 clones analyzed, 78% displayed small deletions or insertions of several nucleotides at the DSB site. Surprisingly, ~8% of recovered mutations involved the capture of one or more DNA fragments. Among 21 clones that had captured DNA, 10 harbored a specific segment of the I-SceI expression plasmid mapping between two replication origins on the plasmid. Four clones had captured a long terminal repeat sequence from an intracisternal A particle (an endogenous retrovirus-like sequence) and one had captured what appears to be a cDNA copy of a moderately repetitive B2 sequence. Additional clones displayed segments of the tk gene and/or microsatellite sequences copied into the DSB. This first systematic study of DNA capture at DSBs in a mammalian genome suggests that DSB repair may play a considerable role in the evolution of eukaryotic genomes.
The Evolution of X-Linked Genomic Imprinting
Authors: Iwasa Yoh , Pomiankowski Andrew
Published: April 2021

We develop a quantitative genetic model to investigate the evolution of X-imprinting. The model compares two forces that select for X-imprinting: genomic conflict caused by polygamy and sex-specific selection. Genomic conflict can only explain small reductions in maternal X gene expression and cannot explain silencing of the maternal X. In contrast, sex-specific selection can cause extreme differences in gene expression, in either direction (lowered maternal or paternal gene expression), even to the point of gene silencing of either the maternal or paternal copy. These conclusions assume that the Y chromosome lacks genetic activity. The presence of an active Y homologue makes imprinting resemble the autosomal pattern, with active paternal alleles (X- and Y-linked) and silenced maternal alleles. This outcome is likely to be restricted as Y-linked alleles are subject to the accumulation of deleterious mutations. Experimental evidence concerning X-imprinting in mouse and human is interpreted in the light of these predictions and is shown to be far more easily explained by sex-specific selection.
Linear and Spatial Organization of Polytene Chromosomes of the African Malaria Mosquito Anopheles funestus
Authors: Sharakhov Igor V , Sharakhova Maria V , Mbogo Charles M , Koekemoer Lizette L , Yan Guiyun
Published: April 2021

Anopheles funestus Giles is one of the major malaria vectors in Africa, but little is known about its genetics. Lack of a cytogenetic map characterized by regions has hindered the progress of genetic research with this important species. This study developed a cytogenetic map of An. funestus using ovarian nurse cell polytene chromosomes. We demonstrate an important application with the cytogenetic map for characterizing various chromosomal inversions for specimens collected from coastal Kenya. The linear and spatial organization of An. funestus polytene chromosomes was compared with the best-studied malaria mosquito, An. gambiae Giles. Comparisons of chromosome morphology between the two species have revealed that the most extensive chromosomal rearrangement occurs in pericentromeric heterochromatin of autosomes. Differences in pericentromeric heterochromatin types correlate with nuclear organization differences between An. funestus and An. gambiae. Attachments of chromosomes to the nuclear envelope strongly depend on the presence of diffusive β-heterochromatin. Thus, An. funestus and An. gambiae exhibit species-specific characteristics in chromosome-linear and -spatial organizations.
Alu Insertion Polymorphisms for the Study of Human Genomic Diversity
Authors: Roy-Engel Astrid M , Carroll Marion L , Vogel Erika , Garber Randall K , Nguyen Son V , Salem Abdel-Halim , Batzer Mark A , Deininger Prescott L
Published: April 2021

Genomic database mining has been a very useful aid in the identification and retrieval of recently integrated Alu elements from the human genome. We analyzed Alu elements retrieved from the GenBank database and identified two new Alu subfamilies, Alu Yb9 and Alu Yc2, and further characterized Yc1 subfamily members. Some members of each of the three subfamilies have inserted in the human genome so recently that about a one-third of the analyzed elements are polymorphic for the presence/absence of the Alu repeat in diverse human populations. These newly identified Alu insertion polymorphisms will serve as identical-by-descent genetic markers for the study of human evolution and forensics. Three previously classified Alu Y elements linked with disease belong to the Yc1 subfamily, supporting the retroposition potential of this subfamily and demonstrating that the Alu Y subfamily currently has a very low amplification rate in the human genome.
Multiple Interactions Among the Components of the Recombinational DNA Repair System in Schizosaccharomyces pombe
Authors: Tsutsui Yasuhiro , Khasanov Fuat K , Shinagawa Hideo , Iwasaki Hiroshi , Bashkirov Vladimir I
Published: April 2021

Schizosaccharomyces pombe Rhp55 and Rhp57 are RecA-like proteins involved in double-strand break (DSB) repair. Here we demonstrate that Rhp55 and Rhp57 proteins strongly interact in vivo, similar to Saccharomyces cerevisiae Rad55p and Rad57p. Mutations in the conserved ATP-binding/hydrolysis folds of both the Rhp55 and Rhp57 proteins impaired their function in DNA repair but not in cell proliferation. However, when combined, ATPase fold mutations in Rhp55p and Rhp57p resulted in severe defects of both functions, characteristic of the deletion mutants. Yeast two-hybrid analysis also revealed other multiple in vivo interactions among S. pombe proteins involved in recombinational DNA repair. Similar to S. cerevisiae Rad51p-Rad54p, S. pombe Rhp51p and Rhp54p were found to interact. Both putative Rad52 homologs in S. pombe, Rad22p and Rti1p, were found to interact with the C-terminal region of Rhp51 protein. Moreover, Rad22p and Rti1p exhibited mutual, as well as self-, interactions. In contrast to the S. cerevisiae interacting pair Rad51p-Rad55p, S. pombe Rhp51 protein strongly interacted with Rhp57 but not with Rhp55 protein. In addition, the Rti1 and Rad22 proteins were found to form a complex with the large subunit of S. pombe RPA. Our data provide compelling evidence that most, but not all, of the protein-protein interactions found in S. cerevisiae DSB repair are evolutionarily conserved.
Characterization of Schizosaccharomyces pombe mcm7+ and cdc23+ (MCM10) and Interactions With Replication Checkpoints
Authors: Liang Debbie T , Forsburg Susan L
Published: April 2021

MCM proteins are required for the proper regulation of DNA replication. We cloned fission yeast mcm7+ and showed it is essential for viability; spores lacking mcm7+ begin S phase later than wild-type cells and arrest with an apparent 2C DNA content. We isolated a novel temperature-sensitive allele, mcm7-98, and also characterized two temperature-sensitive alleles of the fission yeast homolog of MCM10, cdc23+. mcm7-98 and both cdc23ts alleles arrest with damaged chromosomes and an S phase delay. We find that mcm7-98 is synthetically lethal with the other mcmts mutants but does not interact genetically with either cdc23ts allele. However, cdc23-M36 interacts with mcm4ts. Unlike other mcm mutants or cdc23, mcm7-98 is synthetically lethal with checkpoint mutants Δcds1, Δchk1, or Δrad3, suggesting chromosomal defects even at permissive temperature. Mcm7p is a nuclear protein throughout the cell cycle, and its localization is dependent on the other MCM proteins. Our data suggest that the Mcm3p-Mcm5p dimer interacts with the Mcm4p-Mcm6p-Mcm7p core complex through Mcm7p.
Mutations in Mating-Type Genes of the Heterothallic Fungus Podospora anserina Lead to Self-Fertility
Authors: Arnaise Sylvie , Zickler Denise , Le Bilcot Suzanne , Poisier Corinne , Debuchy Robert
Published: April 2021

The heterothallic fungus Podospora anserina has two mating-type alleles termed mat+ and mat−. The mat+ sequence contains one gene, FPR1, while mat− contains three genes: FMR1, SMR1, and SMR2. FPR1 and FMR1 are required for fertilization, which is followed by mitotic divisions of the two parental nuclei inside the female organ. This leads to the formation of plurinucleate cells containing a mixture of parental mat+ and mat− nuclei. Further development requires a recognition between mat+ and mat− nuclei before migration of the mat+/mat− pairs into specialized hyphae in which karyogamy, meiosis, and ascospore formation take place. FPR1, FMR1, and SMR2 control this internuclear recognition step. Initial development of the dikaryotic stage is supposed to require SMR1; disruption of SMR1 results in barren perithecia. In a systematic search for suppressors restoring fertility, we isolated 15 suppressors—all of them mutations in the mating-type genes. These fmr1, smr2, and fpr1 mutants, as well as the strains disrupted for FMR1, SMR2, and FPR1, are weakly self-fertile. They are able to act as the male partner on a strain of the same mating type and give a mixture of biparental and uniparental progeny when crossed with a wild-type strain of opposite mating type. These observations lead us to propose that SMR2, FMR1, and FPR1 act as activators and repressors of fertilization and internuclear recognition functions.
Sex Determination in the Androdioecious Plant Datisca glomerata and Its Dioecious Sister Species D. cannabina
Authors: Wolf Diana E , Satkoski Jessica A , White Kara , Rieseberg Loren H
Published: April 2021

Datisca glomerata is an androdioecious plant species containing male and hermaphroditic individuals. Molecular markers and crossing data suggest that, in both D. glomerata and its dioecious sister species D. cannabina, sex is determined by a single nuclear locus, at which maleness is dominant. Supporting this conclusion, an amplified fragment length polymorphism (AFLP) is heterozygous in males and homozygous recessive in hermaphrodites in three populations of the androdioecious species. Additionally, hermaphrodite × male crosses produced 1:1 sex ratios, while hermaphrodite × hermaphrodite crosses produced almost entirely hermaphroditic offspring. No perfectly sex-linked marker was found in the dioecious species, but all markers associated with sex mapped to a single linkage group and were heterozygous in the male parent. There was no sex-ratio heterogeneity among crosses within D. cannabina collections, but males from one collection produced highly biased sex ratios (94% females), suggesting that there may be sex-linked meiotic drive or a cytoplasmic sex-ratio factor. Interspecific crosses produced only male and female offspring, but no hermaphrodites, suggesting that hermaphroditism is recessive to femaleness. This comparative approach suggests that the hermaphrodite form arose in a dioecious population from a recessive mutation that allowed females to produce pollen.
K+-Channel Transgenes Reduce K+ Currents in Paramecium, Probably by a Post-translational Mechanism
Authors: Ling Kit-Yin , Haynes W John , Oesterle Laura , Kung Ching , Preston Robin R , Saimi Yoshiro
Published: April 2021

PAK11 is 1 of more than 15 members in a gene family that encodes K+-channel pore-forming subunits in Paramecium tetraurelia. Microinjection of PAK11 DNA into macronuclei of wild-type cells results in clonal transformants that exhibit hyperexcitable swimming behaviors reminiscent of certain loss-of-K+-current mutants. PAK2, a distant homolog of PAK11, does not have the same effect. But PAK1, a close homolog of PAK11, induces the same hyperexcitability. Cutting the PAK11 open reading frame (ORF) with restriction enzymes before injection removes this effect entirely. Microinjection of PAK11 ORF flanked by the calmodulin 5′ and 3′ UTRs also induces the same hyperexcitable phenotype. Direct examination of transformed cells under voltage clamp reveals that two different Ca2+-activated K+-specific currents are reduced in amplitude. This reduction does not correlate with a deficit of PAK11 message, since RNA is clearly produced from the injected transgenes. Insertion of a single nucleotide at the start of the PAK11 ORF does not affect the RNA level but completely abolishes the phenotypic transformation. Thus, the reduction of K+ currents by the expression of the K+-channel transgenes reported here is likely to be the consequence of a post-translational event. The complexity of behavioral changes, possible mechanisms, and implications in Paramecium biology are discussed.
Phenotypic and Suppressor Analysis of Defecation in clk-1 Mutants Reveals That Reaction to Changes in Temperature Is an Active Process in Caenorhabditis elegans
Authors: Branicky Robyn , Shibata Yukimasa , Feng Jinliu , Hekimi Siegfried
Published: April 2021

Mutations in the Caenorhabditis elegans maternal-effect gene clk-1 affect cellular, developmental, and behavioral timing. They result in a slowing of the cell cycle, embryonic and postembryonic development, reproduction, and aging, as well as of the defecation, swimming, and pharyngeal pumping cycles. Here, we analyze the defecation behavior in clk-1 mutants, phenotypically and genetically. When wild-type worms are grown at 20° and shifted to a new temperature, the defecation cycle length is significantly affected by that new temperature. In contrast, we find that when clk-1 mutants are shifted, the defecation cycle length is unaffected by that new temperature. We carried out a screen for mutations that suppress the slow defecation phenotype at 20° and identified two distinct classes of genes, which we call dsc for defecation suppressor of clk-1. Mutations in one class also restore the ability to react normally to changes in temperature, while mutations in the other class do not. Together, these results suggest that clk-1 is necessary for readjusting the defecation cycle length in response to changes in temperature. On the other hand, in the absence of clk-1 activity, we observe temperature compensation, a mechanism that maintains a constant defecation period in the face of changes in temperature.
Multiple Regulators of Ty1 Transposition in Saccharomyces cerevisiae Have Conserved Roles in Genome Maintenance
Authors: Scholes Derek T , Banerjee Mukti , Bowen Brian , Curcio M Joan
Published: April 2021

Most Ty1 retrotransposons in the genome of Saccharomyces cerevisiae are transpositionally competent but rarely transpose. We screened yeast mutagenized by insertion of the mTn3-lacZ/LEU2 transposon for mutations that result in elevated Ty1 cDNA-mediated mobility, which occurs by cDNA integration or recombination. Here, we describe the characterization of mTn3 insertions in 21 RTT (regulation of Ty1 transposition) genes that result in 5- to 111-fold increases in Ty1 mobility. These 21 RTT genes are EST2, RRM3, NUT2, RAD57, RRD2, RAD50, SGS1, TEL1, SAE2, MED1, MRE11, SCH9, KAP122, and 8 previously uncharacterized genes. Disruption of RTT genes did not significantly increase Ty1 RNA levels but did enhance Ty1 cDNA levels, suggesting that most RTT gene products act at a step after mRNA accumulation but before cDNA integration. The rtt mutations had widely varying effects on integration of Ty1 at preferred target sites. Mutations in RTT101 and NUT2 dramatically stimulated Ty1 integration upstream of tRNA genes. In contrast, a mutation in RRM3 increased Ty1 mobility >100-fold without increasing integration upstream of tRNA genes. The regulation of Ty1 transposition by components of fundamental pathways required for genome maintenance suggests that Ty1 and yeast have coevolved to link transpositional dormancy to the integrity of the genome.
In Caenorhabditis elegans, the RNA-Binding Domains of the Cytoplasmic Polyadenylation Element Binding Protein FOG-1 Are Needed to Regulate Germ Cell Fates
Authors: Jin Suk-Won , Arno Nancy , Cohen Adam , Shah Amy , Xu Qijin , Chen Nadine , Ellis Ronald E
Published: April 2021

FOG-1 controls germ cell fates in the nematode Caenorhabditis elegans. Sequence analyses revealed that FOG-1 is a cytoplasmic polyadenylation element binding (CPEB) protein; similar proteins from other species have been shown to bind messenger RNAs and regulate their translation. Our analyses of fog-1 mutations indicate that each of the three RNA-binding domains of FOG-1 is essential for activity. In addition, biochemical tests show that FOG-1 is capable of binding RNA sequences in the 3′-untranslated region of its own message. Finally, genetic assays reveal that fog-1 functions zygotically, that the small fog-1 transcript has no detectable function, and that missense mutations in fog-1 cause a dominant negative phenotype. This last observation suggests that FOG-1 acts in a complex, or as a multimer, to regulate translation. On the basis of these data, we propose that FOG-1 binds RNA to regulate germ cell fates and that it does so by controlling the translation of its targets. One of these targets might be the fog-1 transcript itself.
The Gypsy Insulator of Drosophila Affects Chromatin Structure in a Directional Manner
Authors: Chen Siquan , Corces Victor G
Published: April 2021

Chromatin insulators are thought to regulate gene expression by establishing higher-order domains of chromatin organization, although the specific mechanisms by which these sequences affect enhancer-promoter interactions are not well understood. Here we show that the gypsy insulator of Drosophila can affect chromatin structure. The insulator itself contains several DNase I hypersensitive sites whose occurrence is dependent on the binding of the Suppressor of Hairy-wing [Su(Hw)] protein. The presence of the insulator in the 5′ region of the yellow gene increases the accessibility of the DNA to nucleases in the promoter-proximal, but not the promoter-distal, region. This increase in accessibility is not due to alterations in the primary chromatin fiber, because the number and position of the nucleosomes appears to be the same in the presence or absence of the insulator. Binding of the Su(Hw) protein to insulator DNA is not sufficient to induce changes in chromatin accessibility, and two domains of this protein, presumed to be involved in interactions with other insulator components, are essential for this effect. The presence of Modifier of mdg4 [Mod(mdg4)] protein, a second component of the gypsy insulator, is required to induce these alterations in chromatin accessibility. The results suggest that the gypsy insulator affects chromatin structure and offer insights into the mechanisms by which insulators affect enhancer-promoter interactions.
Directional Selection and the Site-Frequency Spectrum
Authors: Bustamante Carlos D , Wakeley John , Sawyer Stanley , Hartl Daniel L
Published: April 2021

In this article we explore statistical properties of the maximum-likelihood estimates (MLEs) of the selection and mutation parameters in a Poisson random field population genetics model of directional selection at DNA sites. We derive the asymptotic variances and covariance of the MLEs and explore the power of the likelihood ratio tests (LRT) of neutrality for varying levels of mutation and selection as well as the robustness of the LRT to deviations from the assumption of free recombination among sites. We also discuss the coverage of confidence intervals on the basis of two standard-likelihood methods. We find that the LRT has high power to detect deviations from neutrality and that the maximum-likelihood estimation performs very well when the ancestral states of all mutations in the sample are known. When the ancestral states are not known, the test has high power to detect deviations from neutrality for negative selection but not for positive selection. We also find that the LRT is not robust to deviations from the assumption of independence among sites.
Heterosis, Marker Mutational Processes and Population Inbreeding History
Authors: Tsitrone Anne , Rousset François , David Patrice
Published: April 2021

Genotype-fitness correlations (GFC) have previously been studied using allozyme markers and have often focused on short-term processes such as recent inbreeding. Thus, models of GFC usually neglect marker mutation and only use heterozygosity as a genotypic index. Recently, GFC have also been reported (i) with DNA markers such as microsatellites, characterized by high mutation rates and specific mutational processes and (ii) using new individual genotypic indices assumed to be more precise than heterozygosity. The aim of this article is to evaluate the theoretical impact of marker mutation on GFC. We model GFC due to short-term processes generated by the current breeding system (partial selfing) and to long-term processes generated by past population history (hybridization). Various mutation rates and mutation models corresponding to different kinds of molecular markers are considered. Heterozygosity is compared to other genotypic indices designed for specific marker types. Highly mutable markers (such as microsatellites) are particularly suitable for the detection of GFC that evolve in relation to short-term processes, whereas GFC due to long-term processes are best observed with intermediate mutation rates. Irrespective of the marker type and population scenario, heterozygosity usually provides higher correlations than other genotypic indices under most biologically plausible conditions.
Meiotic Deletion at the BUF1 Locus of the Fungus Magnaporthe grisea Is Controlled by Interaction With the Homologous Chromosome
Authors: Farman Mark L
Published: April 2021

The Magnaporthe grisea BUF1 gene suffers high-frequency mutation in certain genetic crosses, resulting in buff-colored progeny. Analysis of 16 buf1 mutants arising from a cross with a mutation frequency of 25% revealed that, in every case, the BUF1 gene was deleted. The deletions occurred in only one of the parental chromosomes and were due to intrachromosomal recombination. Tetrad analysis revealed that deletions occurred in 44% of meioses and usually affected both chromatids of the mutable chromosome. This suggests that they happen before the premeiotic round of DNA synthesis. However, they were also almost entirely restricted to heteroallelic crosses. This, together with the discovery of numerous repetitive elements that were present only in the mutable BUF1 locus, suggests that the deletion process is sensitive to pairing interactions between homologous chromosomes, such that only unpaired loci are subject to deletion. Given that karyogamy is not supposed to occur until after premeiotic DNA replication in Pyrenomycetous fungi such as M. grisea, this latter observation would place the time of deletion during, or after, DNA synthesis. These conflicting results suggest that karyogamy might actually precede DNA replication in Pyrenomycetous fungi or that parts of the genome remain unreplicated until after karyogamy and subsequent chromosome pairing have taken place.
Telomere elongation (Tel), a New Mutation in Drosophila melanogaster That Produces Long Telomeres
Authors: Siriaco Giorgia M , Cenci Giovanni , Haoudi Abdelali , Champion Larry E , Zhou Chun , Gatti Maurizio , Mason James M
Published: April 2021

In most eukaryotes telomeres are extended by telomerase. Drosophila melanogaster, however, lacks telomerase, and telomere-specific non-LTR retrotransposons, HeT-A and TART, transpose specifically to chromosome ends. A Drosophila strain, Gaiano, that has long telomeres has been identified. We extracted the major Gaiano chromosomes into an Oregon-R genetic background and examined the resulting stocks after 60 generations. In situ hybridization using HeT-A and TART sequences showed that, in stocks carrying either the X or the second chromosome from Gaiano, only the Gaiano-derived chromosomes display long telomeres. However, in stocks carrying the Gaiano third chromosome, all telomeres are substantially elongated, indicating that the Gaiano chromosome 3 carries a factor that increases HeT-A and TART addition to the telomeres. We show that this factor, termed Telomere elongation (Tel), is dominant and localizes as a single unit to 69 on the genetic map. The long telomeres tend to associate with each other in both polytene and mitotic cells. These associations depend on telomere length rather than the presence of Tel. Associations between metaphase chromosomes are resolved during anaphase, suggesting that they are mediated by either proteinaceous links or DNA hydrogen bonding, rather than covalent DNA-DNA bonds.
Y Chromosomal Evidence for the Origins of Oceanic-Speaking Peoples
Authors: Hurles Matthew E , Nicholson Jayne , Bosch Elena , Renfrew Colin , Sykes Bryan C , Jobling Mark A
Published: April 2021

A number of alternative hypotheses seek to explain the origins of the three groups of Pacific populations—Melanesians, Micronesians, and Polynesians—who speak languages belonging to the Oceanic subfamily of Austronesian languages. To test these various hypotheses at the genetic level, we assayed diversity within the nonrecombining portion of the Y chromosome, which contains within it a relatively simple record of the human past and represents the most informative haplotypic system in the human genome. High-resolution haplotypes combining binary, microsatellite, and minisatellite markers were generated for 390 Y chromosomes from 17 Austronesian-speaking populations in southeast Asia and the Pacific. Nineteen paternal lineages were defined and a Bayesian analysis of coalescent simulations was performed upon the microsatellite diversity within lineages to provide a temporal aspect to their geographical distribution. The ages and distributions of these lineages provide little support for the dominant archeo-linguistic model of the origins of Oceanic populations that suggests that these peoples represent the Eastern fringe of an agriculturally driven expansion initiated in southeast China and Taiwan. Rather, most Micronesian and Polynesian Y chromosomes appear to originate from different source populations within Melanesia and Eastern Indonesia. The Polynesian outlier, Kapingamarangi, is demonstrated to be an admixed Micronesian/Polynesian population. Furthermore, it is demonstrated that a geographical rather than linguistic classification of Oceanic populations best accounts for their extant Y chromosomal diversity.
The Ess1 Prolyl Isomerase Is Required for Growth and Morphogenetic Switching inCandida albicans
Authors: Devasahayam Gina , Chaturvedi Vishnu , Hanes Steven D
Published: April 2021

Prolyl-isomerases (PPIases) are found in all organisms and are important for the folding and activity of many proteins. Of the 13 PPIases in Saccharomyces cerevisiae only Ess1, a parvulin-class PPIase, is essential for growth. Ess1 is required to complete mitosis, and Ess1 and its mammalian homolog, Pin1, interact directly with RNA polymerase II. Here, we isolate the ESS1 gene from the pathogenic fungus Candida albicans and show that it is functionally homologous to the S. cerevisiae ESS1. We generate conditional-lethal (ts) alleles of C. albicans ESS1 and use these mutations to demonstrate that ESS1 is essential for growth in C. albicans. We also show that reducing the dosage or activity of ESS1 blocks morphogenetic switching from the yeast to the hyphal and pseudohyphal forms under certain conditions. Analysis of double mutants of ESS1 and TUP1 or CPH1, two genes known to be involved in morphogenetic switching, suggests that ESS1 functions in the same pathway as CPH1 and upstream of or in parallel to TUP1. Given that switching is important for virulence of C. albicans, inhibitors of Ess1 might be useful as antifungal agents.
Sex Determination Signals Control ovo-B Transcription in Drosophila melanogaster Germ Cells
Authors: Andrews Justen , Oliver Brian
Published: April 2021

Nonautonomous inductive signals from the soma and autonomous signals due to a 2X karyotype determine the sex of Drosophila melanogaster germ cells. These two signals have partially overlapping influences on downstream sex determination genes. The upstream OVO-B transcription factor is required for the viability of 2X germ cells, regardless of sexual identity, and for female germline sexual identity. The influence of inductive and autonomous signals on ovo expression has been controversial. We show that ovo-B is strongly expressed in the 2X germ cells in either a male or a female soma. This indicates that a 2X karyotype controls ovo-B expression in the absence of inductive signals from the female soma. However, we also show that female inductive signals positively regulate ovo-B transcription in the 1X germ cells that do not require ovo-B function. Genetic analysis clearly indicates that inductive signals from the soma are not required for ovo-B function in 2X germ cells. Thus, while somatic inductive signals and chromosome karyotype have overlapping regulatory influences, a 2X karyotype is a critical germline autonomous determinant of ovo-B function in the germline.
The Drosophila inebriated-Encoded Neurotransmitter/Osmolyte Transporter: Dual Roles in the Control of Neuronal Excitability and the Osmotic Stress Response
Authors: Huang Xi , Huang Yanmei , Chinnappan Raj , Bocchini Claire , Gustin Michael C , Stern Michael
Published: April 2021

Water reabsorption by organs such as the mammalian kidney and insect Malpighian tubule/hindgut requires a region of hypertonicity within the organ. To balance the high extracellular osmolarity, cells within these regions accumulate small organic molecules called osmolytes. These osmolytes can accumulate to a high level without toxic effects on cellular processes. Here we provide evidence consistent with the possibility that the two protein isoforms encoded by the inebriated (ine) gene, which are members of the Na+/Cl−-dependent neurotransmitter/osmolyte transporter family, perform osmolyte transport within the Malpighian tubule and hindgut. We show that ine mutants lacking both isoforms are hypersensitive to osmotic stress, which we assayed by maintaining flies on media containing NaCl, KCl, or sorbitol, and that this hypersensitivity is completely rescued by high-level ectopic expression of the ine-RB isoform. We provide evidence that this hypersensitivity represents a role for ine that is distinct from the increased neuronal excitability phenotype of ine mutants. Finally, we show that each ine genotype exhibits a “threshold” [NaCl]: long-term maintenance on NaCl-containing media above, but not below, the threshold causes lethality. Furthermore, this threshold value increases with the amount of ine activity. These data suggest that ine mutations confer osmotic stress sensitivity by preventing osmolyte accumulation within the Malpighian tubule and hindgut.
Identification of Circadian-Clock-Regulated Enhancers and Genes of Drosophila melanogaster by Transposon Mobilization and Luciferase Reporting of Cyclical Gene Expression
Authors: Stempfl Thomas , Vogel Marion , Szabo Gisela , Wülbeck Corinna , Liu Jian , Hall Jeffrey C , Stanewsky Ralf
Published: April 2021

A new way was developed to isolate rhythmically expressed genes in Drosophila by modifying the classic enhancer-trap method. We constructed a P element containing sequences that encode firefly luciferase as a reporter for oscillating gene expression in live flies. After generation of 1176 autosomal insertion lines, bioluminescence screening revealed rhythmic reporter-gene activity in 6% of these strains. Rhythmically fluctuating reporter levels were shown to be altered by clock mutations in genes that specify various circadian transcription factors or repressors. Intriguingly, rhythmic luminescence in certain lines was affected by only a subset of the pacemaker mutations. By isolating genes near 13 of the transposon insertions and determining their temporal mRNA expression pattern, we found that four of the loci adjacent to the trapped enhancers are rhythmically expressed. Therefore, this approach is suitable for identifying genetic loci regulated by the circadian clock. One transposon insert caused a mutation in the rhythmically expressed gene numb. This novel numb allele, as well as previously described ones, was shown to affect the fly's rhythm of locomotor activity. In addition to its known role in cell fate determination, this gene and the phosphotyrosine-binding protein it encodes are likely to function in the circadian system.
Sex-Specific Recombination Rates in Zebrafish (Danio rerio)
Authors: Singer Amy , Perlman Hodel , Yan YiLin , Walker Charlene , Corley-Smith Graham , Brandhorst Bruce , Postlethwait John
Published: April 2021

In many organisms, the rate of genetic recombination is not uniform along the length of chromosomes or between sexes. To compare the relative recombination rates during meiosis in male and female zebrafish, we constructed a genetic map based on male meiosis. We developed a meiotic mapping panel of 94 androgenetic haploid embryos that were scored for genetic polymorphisms. The resulting male map was compared to female and sex-average maps. We found that the recombination rate in male meiosis is dramatically suppressed relative to that of female meiosis, especially near the centromere. These findings have practical applications for experimental design. The use of exclusively female meiosis in a positional cloning project maximizes the ratio of genetic map distance to physical distance. Alternatively, the use of exclusively male meiosis to localize a mutation initially to a linkage group or to maintain relationships of linked alleles minimizes recombination, thereby facilitating some types of analysis.
Caenorhabditis elegans unc-37/groucho Interacts Genetically With Components of the Transcriptional Mediator Complex
Authors: Zhang Hong , Emmons Scott W
Published: April 2021

Groucho functions as a general corepressor by modulating chromatin structure and has a widespread role in many developmental processes. Here we show that Groucho may also interact with the basal transcriptional machinery. Mutations in Caenorhabditis elegans groucho interact with mutations in components of the transcriptional Mediator complex, resulting in synthetic lethality and loss of male sensory neurons.
Genetic and Molecular Analysis of Region 88E9;88F2 in Drosophila melanogaster, Including the ear Gene Related to Human Factors Involved in Lineage-Specific Leukemias
Authors: Zraly Claudia B , Feng Yun , Dingwall Andrew K
Published: April 2021

We identified and characterized the Drosophila gene ear (ENL/AF9-related), which is closely related to mammalian genes that have been implicated in the onset of acute lymphoblastic and myelogenous leukemias when their products are fused as chimeras with those of human HRX, a homolog of Drosophila trithorax. The ear gene product is present in all early embryonic cells, but becomes restricted to specific tissues in late embryogenesis. We mapped the ear gene to cytological region 88E11-13, near easter, and showed that it is deleted by Df(3R)ea5022rx1, a small, cytologically invisible deletion. Annotation of the completed Drosophila genome sequence suggests that this region might contain as many as 26 genes, most of which, including ear, are not represented by mutant alleles. We carried out a large-scale noncom-plementation screen using Df(3R)ea5022rx1 and chemical (EMS) mutagenesis from which we identified sevenc novel multi-allele recessive lethal complementation groups in this region. An overlapping deficiency, Df(3R)Po4, allowed us to map several of these groups to either the proximal or the distal regions of Df(3R)ea5022rx1. One of these complementation groups likely corresponds to the ear gene as judged by map location, terminal phenotype, and reduction of EAR protein levels.
History of Infection With Different Male-Killing Bacteria in the Two-Spot Ladybird BeetleAdalia bipunctataRevealed Through Mitochondrial DNA Sequence Analysis
Authors: Hinrich J , Schulenburg G v d , Hurst Gregory D D , Tetzlaff Dagmar , Booth Gwendolen E , Zakharov Ilia A , Majerus Michael E N
Published: April 2021

The two-spot ladybird beetle Adalia bipunctata (Coleoptera: Coccinellidae) is host to four different intracellular maternally inherited bacteria that kill male hosts during embryogenesis: one each of the genus Rickettsia (α-Proteobacteria) and Spiroplasma (Mollicutes) and two distinct strains of Wolbachia (α-Proteobacteria). The history of infection with these male-killers was explored using host mitochondrial DNA, which is linked with the bacteria due to joint maternal inheritance. Two variable regions, 610 bp of cytochrome oxidase subunit I and 563 bp of NADH dehydrogenase subunit 5, were isolated from 52 A. bipunctata with known infection status and different geographic origin from across Eurasia. Two outgroup taxa were also considered. DNA sequence analysis revealed that the distribution of mitochondrial haplotypes is not associated with geography. Rather, it correlates with infection status, confirming linkage disequilibrium between mitochondria and bacteria. The data strongly suggest that the Rickettsia male-killer invaded the host earlier than the other taxa. Further, the male-killing Spiroplasma is indicated to have undergone a recent and extensive spread through host populations. In general, male-killing in A. bipunctata seems to represent a highly dynamic system, which should prove useful in future studies on the evolutionary dynamics of this peculiar type of symbiont-host association.
Quantitative Trait Loci for Inflorescence Development in Arabidopsis thaliana
Authors: Ungerer Mark C , Halldorsdottir Solveig S , Modliszewski Jennifer L , Mackay Trudy F C , Purugganan Michael D
Published: April 2021

Variation in inflorescence development patterns is a central factor in the evolutionary ecology of plants. The genetic architectures of 13 traits associated with inflorescence developmental timing, architecture, rosette morphology, and fitness were investigated in Arabidopsis thaliana, a model plant system. There is substantial naturally occurring genetic variation for inflorescence development traits, with broad sense heritabilities computed from 21 Arabidopsis ecotypes ranging from 0.134 to 0.772. Genetic correlations are significant for most (64/78) pairs of traits, suggesting either pleiotropy or tight linkage among loci. Quantitative trait locus (QTL) mapping indicates 47 and 63 QTL for inflorescence developmental traits in Ler × Col and Cvi × Ler recombinant inbred mapping populations, respectively. Several QTL associated with different developmental traits map to the same Arabidopsis chromosomal regions, in agreement with the strong genetic correlations observed. Epistasis among QTL was observed only in the Cvi × Ler population, and only between regions on chromosomes 1 and 5. Examination of the completed Arabidopsis genome sequence in three QTL regions revealed between 375 and 783 genes per region. Previously identified flowering time, inflorescence architecture, floral meristem identity, and hormone signaling genes represent some of the many candidate genes in these regions.
UV Irradiation Causes the Loss of Viable Mitotic Recombinants in Schizosaccharomyces pombe Cells Lacking the G2/M DNA Damage Checkpoint
Authors: Osman Fekret , Tsaneva Irina R , Whitby Matthew C , Doe Claudette L
Published: April 2021

Elevated mitotic recombination and cell cycle delays are two of the cellular responses to UV-induced DNA damage. Cell cycle delays in response to DNA damage are mediated via checkpoint proteins. Two distinct DNA damage checkpoints have been characterized in Schizosaccharomyces pombe: an intra-S-phase checkpoint slows replication and a G2/M checkpoint stops cells passing from G2 into mitosis. In this study we have sought to determine whether UV damage-induced mitotic intrachromosomal recombination relies on damage-induced cell cycle delays. The spontaneous and UV-induced recombination phenotypes were determined for checkpoint mutants lacking the intra-S and/or the G2/M checkpoint. Spontaneous mitotic recombinants are thought to arise due to endogenous DNA damage and/or intrinsic stalling of replication forks. Cells lacking only the intra-S checkpoint exhibited no UV-induced increase in the frequency of recombinants above spontaneous levels. Mutants lacking the G2/M checkpoint exhibited a novel phenotype; following UV irradiation the recombinant frequency fell below the frequency of spontaneous recombinants. This implies that, as well as UV-induced recombinants, spontaneous recombinants are also lost in G2/M mutants after UV irradiation. Therefore, as well as lack of time for DNA repair, loss of spontaneous and damage-induced recombinants also contributes to cell death in UV-irradiated G2/M checkpoint mutants.
The Novel Adaptor Protein, Mti1p, and Vrp1p, a Homolog of Wiskott-Aldrich Syndrome Protein-Interacting Protein (WIP), May Antagonistically Regulate Type I Myosins in Saccharomyces cerevisiae
Authors: Mochida Junko , Yamamoto Takaharu , Fujimura-Kamada Konomi , Tanaka Kazuma
Published: April 2021

Type I myosins in yeast, Myo3p and Myo5p (Myo3/5p), are involved in the reorganization of the actin cytoskeleton. The SH3 domain of Myo5p regulates the polymerization of actin through interactions with both Las17p, a homolog of mammalian Wiskott-Aldrich syndrome protein (WASP), and Vrp1p, a homolog of WASP-interacting protein (WIP). Vrp1p is required for both the localization of Myo5p to cortical patch-like structures and the ATP-independent interaction between the Myo5p tail region and actin filaments. We have identified and characterized a new adaptor protein, Mti1p (Myosin tail region-interacting protein), which interacts with the SH3 domains of Myo3/5p. Mti1p co-immunoprecipitated with Myo5p and Mti1p-GFP co-localized with cortical actin patches. A null mutation of MTI1 exhibited synthetic lethal phenotypes with mutations in SAC6 and SLA2, which encode actin-bundling and cortical actin-binding proteins, respectively. Although the mti1 null mutation alone did not display any obvious phenotype, it suppressed vrp1 mutation phenotypes, including temperature-sensitive growth, abnormally large cell morphology, defects in endocytosis and salt-sensitive growth. These results suggest that Mti1p and Vrp1p antagonistically regulate type I myosin functions.