A key event in meiosis is the conversion of a small subset of double strand breaks into interhomolog crossovers. In this study, we demonstrate that Caenorhabditis elegans male spermatogenesis has less robust mechanisms than hermaphrodite oogenesis for ensuring and limiting the conversion of double strand breaks into crossovers. This is not a consequence of differences in meiotic prophase timing, sex chromosome genotype, or the presence or absence of germline apoptosis. Using the cyclin-like crossover marker COSA-1, we show that males have a linear response in converting increasing numbers of double strand breaks into crossovers, suggesting weakened crossover homeostasis. While the topoisomerase SPO-11, responsible for initiating meiotic double strand breaks, has an extended period of activity in males as in hermaphrodites, we discovered that COSA-1 foci form at the very end of meiotic prophase in the absence of SPO-11 during spermatogenesis. These COSA-1-marked sites are also independent of homologous recombination, and Topoisomerases I and II. We find that the synaptonemal complex, which holds homologs in proximity, differently modulates COSA-1 enrichment to chromosomes in the absence of SPO-11 in males and hermaphrodites. Together, these findings suggest that males have less robust crossover control and that there are previously unrecognized lesions or structures at the end of meiotic prophase in spermatocytes that can accumulate CO markers.

• Publication type
• Journal Article MeSH
• Preprint MeSH

Faithful meiotic segregation requires pairwise alignment of the homologous chromosomes and their synaptonemal complex (SC) mediated stabilization. Here, we investigate factors that promote and coordinate these events during C. elegans meiosis. We identify BRA-2 (BMP Receptor Associated family member 2) as an interactor of HIM-17, previously shown to promote double-strand break formation. We found that loss of bra-2 impairs synapsis elongation without affecting homolog recognition, chromosome movement or SC maintenance. Epistasis analyses reveal previously unrecognized activities for HIM-17 in regulating homolog pairing and SC assembly in a partially overlapping manner with BRA-2. We show that removing bra-2 or him-17 restores nuclear clustering, recruitment of PLK-2 at the nuclear periphery, and abrogation of ectopic synapsis in htp-1 mutants, suggesting intact CHK-2-mediated signaling and presence of a barrier that prevents SC polymerization in the absence of homology. Our findings shed light on the regulatory mechanisms ensuring faithful pairing and synapsis.

• MeSH
• Caenorhabditis elegans * genetics   metabolism   cytology   MeSH
• Meiosis * genetics   physiology   MeSH
• Mutation MeSH
• Chromosome Pairing * genetics   MeSH
• Cell Cycle Proteins * metabolism   genetics   MeSH
• Caenorhabditis elegans Proteins * metabolism   genetics   MeSH
• Synaptonemal Complex metabolism   genetics   MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Htp-1 protein, C elegans MeSH Browser
• Cell Cycle Proteins * MeSH
• Caenorhabditis elegans Proteins * MeSH

Double-strand breaks (DSBs) are the most deleterious lesions experienced by our genome. Yet, DSBs are intentionally induced during gamete formation to promote the exchange of genetic material between homologous chromosomes. While the conserved topoisomerase-like enzyme Spo11 catalyzes DSBs, additional regulatory proteins-referred to as "Spo11 accessory factors"- regulate the number, timing, and placement of DSBs during early meiotic prophase ensuring that SPO11 does not wreak havoc on the genome. Despite the importance of the accessory factors, they are poorly conserved at the sequence level suggesting that these factors may adopt unique functions in different species. In this work, we present a detailed analysis of the genetic and physical interactions between the DSB factors in the nematode Caenorhabditis elegans providing new insights into conserved and novel functions of these proteins. This work shows that HIM-5 is the determinant of X-chromosome-specific crossovers and that its retention in the nucleus is dependent on DSB-1, the sole accessory factor that interacts with SPO-11. We further provide evidence that HIM-5 coordinates the actions of the different accessory factors sub-groups, providing insights into how components on the DNA loops may interact with the chromosome axis.

• Keywords
• C. elegans, Crossover, SPO11, double-strand break, meiosis,
• Publication type
• Journal Article MeSH
• Preprint MeSH

Meiotic chromosome segregation relies on programmed DNA double-strand break induction. These are in turn repaired by homologous recombination, generating physical attachments between the parental chromosomes called crossovers. A subset of breaks yields recombinant outcomes, while crossover-independent mechanisms repair the majority of lesions. The balance between different repair pathways is crucial to ensure genome integrity. We show that Caenorhabditis elegans BRC-1/BRCA1-BRD-1/BARD1 and PARG-1/PARG form a complex in vivo, essential for accurate DNA repair in the germline. Simultaneous depletion of BRC-1 and PARG-1 causes synthetic lethality due to reduced crossover formation and impaired break repair, evidenced by hindered RPA-1 removal and presence of aberrant chromatin bodies in diakinesis nuclei, whose formation depends on spo-11 function. These factors undergo a similar yet independent loading in developing oocytes, consistent with operating in different pathways. Abrogation of KU- or Theta-mediated end joining elicits opposite effects in brc-1; parg-1 doubles, suggesting a profound impact in influencing DNA repair pathway choice by BRC-1-PARG-1. Importantly, lack of PARG-1 catalytic activity suppresses untimely accumulation of RAD-51 foci in brc-1 mutants but is only partially required for fertility. Our data show that BRC-1/BRD-1-PARG-1 joint function is essential for genome integrity in meiotic cells by regulating multiple DNA repair pathways.

• MeSH
• Caenorhabditis elegans genetics   MeSH
• DNA-Binding Proteins * metabolism   MeSH
• DNA Breaks, Double-Stranded MeSH
• Gametogenesis MeSH
• Meiosis MeSH
• DNA Repair * MeSH
• GTPase-Activating Proteins * metabolism   MeSH
• Caenorhabditis elegans Proteins * metabolism   MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Research Support, N.I.H., Extramural MeSH
• Names of Substances
• BRC-1 protein, C elegans MeSH Browser
• BRC-2 protein, C elegans MeSH Browser
• DNA-Binding Proteins * MeSH
• GTPase-Activating Proteins * MeSH
• Caenorhabditis elegans Proteins * MeSH

Generation of functional gametes is accomplished through a multilayered and finely orchestrated succession of events during meiotic progression. In the Caenorhabditis elegans germline, the HORMA-domain-containing protein HTP-3 plays pivotal roles for the establishment of chromosome axes and the efficient induction of programmed DNA double-strand breaks, both of which are crucial for crossover formation. Double-strand breaks allow for accurate chromosome segregation during the first meiotic division and therefore are an essential requirement for the production of healthy gametes. Phosphorylation-dependent regulation of HORMAD protein plays important roles in controlling meiotic chromosome behavior. Here, we document a phospho-site in HTP-3 at Serine 285 that is constitutively phosphorylated during meiotic prophase I. pHTP-3S285 localization overlaps with panHTP-3 except in nuclei undergoing physiological apoptosis, in which pHTP-3 is absent. Surprisingly, we observed that phosphorylation of HTP-3 at S285 is independent of the canonical kinases that control meiotic progression in nematodes. During meiosis, the htp-3(S285A) mutant displays accelerated RAD-51 turnover, but no other meiotic abnormalities. Altogether, these data indicate that the Ser285 phosphorylation is independent of canonical meiotic protein kinases and does not regulate HTP-3-dependent meiotic processes. We propose a model wherein phosphorylation of HTP-3 occurs through noncanonical or redundant meiotic kinases and/or is likely redundant with additional phospho-sites for function in vivo.

• Keywords
• Caenorhabditis elegans meiosis, HORMA-domain proteins, HTP-3,
• MeSH
• Caenorhabditis elegans genetics   metabolism   MeSH
• Phosphorylation MeSH
• Meiosis * MeSH
• Cell Cycle Proteins genetics   MeSH
• Caenorhabditis elegans Proteins * metabolism   MeSH
• Chromosome Segregation MeSH
• Serine metabolism   MeSH
• Synaptonemal Complex metabolism   MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Research Support, N.I.H., Extramural MeSH
• Names of Substances
• Cell Cycle Proteins MeSH
• Caenorhabditis elegans Proteins * MeSH
• Serine MeSH