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Geetha, S.

Publications and source records attributed to Geetha, S..

3 recordsLinked to original sources
bioRxiv2026

ZHP-2/HEI10 generates CO precursors and triggers procrossover factor coarsening and CO formation through Polo kinase recruitment

During meiosis, programmed DNA double-strand breaks (DSBs) are repaired with the homolog to form crossovers (COs) essential for chromosome segregation, or noncrossovers (nCOs) to restore genomic integrity. Only a few recombination intermediates will become COs and these sites are progressively enriched in proCO factors at the expense of nCO sites, referred to as coarsening. Here, we show that in C. elegans this process is engineered by ZHP-2/HEI10, a conserved E3 ligase that has functions at early and late stages of CO formation. Early on, ZHP-2-mediated loss of RMH-1/RMI1 and HIM-6/BLM from strand exchange intermediates is required for joint molecule formation and nCO repair. In zhp-2 mutants, proCO factors accumulate at HR sites, leading to defects in CO formation and CO spacing. We find that Polo kinase recruitment to a ZHP-2 at CO precursors signals an end to further DSB formation, and triggers proCO factor coarsening and CO formation. We propose that ZHP-2 disassembles proCO factors from recombination intermediates until it is inactivated at CO precursors through Polo kinase recruitment, leading to stabilization of proCO factors, and resolution of joint molecules as crossovers. Our study reveals that ZHP-2/HEI10 is the central component of a Polo kinase-driven switch that initiates proCO factor coarsening and execution of crossing over.

cell biology↗
bioRxiv2026

BRC-2/BRCA2-RIPR-1 mediated constraints on homologous recombination execution are spatiotemporally regulated during meiosis

Homologous recombination-dependent processing of meiotic double-strand breaks is crucial to generate functional gametes. The breast and ovarian cancer susceptibility gene BRCA2 is essential for the loading of RAD51-DMC1 recombinases at DNA breaks to allow accurate repair. Here, we identify the novel protein RIPR-1 as a binding partner of Caenorhabditis elegans BRC-2/BRCA2. RIPR-1 and BRC-2 form an obligate complex both in vitro and in vivo and display interdependent loading in developing oocytes. Loss of ripr-1 results in the complete destabilization of BRC-2, while brc-2 is only partially required to preserve RIPR-1 stability. Strikingly, we found a dramatic accumulation of RAD-51 in late pachytene cells of both ripr-1 and brc-2 nulls, unveiling a BRCA2-independent pathway for recruitment of RAD-51 at resected meiotic DNA breaks. RIPR-1 enhances BRC-2 binding to single-stranded DNA and unlike the individual components, the assembled RIPR-1-BRC-2 complex can also bind double-stranded DNA in vitro. Surprisingly, we observe that RAD-51-dependent crossover designation still occurs in absence of RIPR-1-BRC-2, indicating partial, and stage-dependent constraints on homologous recombination execution. Altogether, our work identifies a novel BRC-2 interactor and sheds new light on HR-mediated regulation of DNA repair during meiosis.

Cell Biology↗
bioRxiv2026

G protein-coupled receptor SmGPCR9 interacts with neuropeptides and controls spermatogenesis in Schistosoma mansoni

Schistosomiasis is a neglected tropical disease caused by parasitic flatworms of the genus Schistosoma, impacting hundreds of millions of people and animals globally. Disease pathology primarily originates from host immune responses to parasite eggs, which are produced only when female schistosomes are continuously paired with males. Past research focused on pairing-dependent female sexual maturation, while scarce data exist for the males reproductive biology. In this study, we characterized the G protein-coupled receptor Smgpcr9 (Smp_244240), an orphan Class A (Rhodopsin-like) GPCR with a testis-preferential and pairing-influenced expression profile in S. mansoni males. Previous bulk RNA-seq analyses of adult worms and their isolated gonads revealed that Smgpcr9 belongs to a subgroup of GPCR genes with abundant testis-preferential and pairing-influenced transcript levels in males but low and extremely low expression in unpaired and paired females, respectively. This male-/unpaired female-biased expression pattern mirrors that of neuropeptide (npp) genes of S. mansoni such as Smnpp26 and Smnpp41. In a deorphanization approach using yeast-two-hybrid analyses, GPCR internalization experiments, bioluminescence resonance energy transfer assays, and by modeling and docking analyses, we provide first evidence that both NPPs can interact with SmGPCR9. Furthermore, we optimized a GPCR RNAi approach and achieved efficient transcript knockdown (> 90%) enabling robust functional characterization of Smgpcr9. Following RNAi, physiological and morphological analyses revealed that SmGPCR9 regulates key aspects of male reproductive biology like testis morphology and spermatogenesis. Remarkably, ovary structure and egg production were also affected in paired females post RNAi. We observed similar phenotypes plus motility constraints and reduced stem-cell proliferation in both sexes upon RNAi of Smnpp26 and Smnpp41. In all cases, RNAi downstream analyses by RT-qPCR of marker genes substantiated the observed phenotypic effects. These results strongly indicate the importance of SmGPCR9, SmNPP26, and SmNPP41 for spermatogenesis and further physiological processes in male and female S. mansoni. Author SummaryResearch of the reproductive biology of schistosomes focused mainly on females so far, which upon pairing sexually mature to produce eggs that are important for the life cycle maintenance but also for the pathogenesis of schistosomiasis, the infectious disease caused by these parasites. We investigated a yet unknown G protein-coupled receptor, Smgpcr9, which showed a testis-preferential and pairing-influenced expression profile in Schistosoma mansoni males. To this end, we optimized an RNA interference (RNAi) approach for knockdown analysis, identified neuropeptides (NPPs) as potential ligands by different biochemical approaches and modeling and docking analyses, and we investigated the roles of SmGPCR9 and two interacting NPPs, SmNPP26 and SmNPP41, by physiological, microscopical, and molecular techniques. Our results strongly suggest that SmGPCR9 and both NPPs regulate spermatogenesis. Furthermore, we detected effects on ovary morphology, egg production, and stem-cell proliferation of paired females post RNAi. Taken together, we deorphanized SmGPCR9 and showed for the first time the essential role of a so far uncharacterized GPCR and two interacting neuropeptides for spermatogenesis. Our results shed first light on spermatogenesis regulatory processes controlled by GPCRs and neuropeptides in male S. mansoni and thus expand our understanding of the roles of GPCR-NPP signaling for schistosome reproductive biology.

molecular biology↗