BPS2026 – Characterization of interactions among crossover-promoting factors in C. elegans meiosis

Accurate chromosome segregation in meiosis I requires at least one crossover (CO) per homolog pair. While CO formation is promoted by a conserved set of “ZMM” proteins, the molecular interactions that coordinate CO designation with chromosome structure remain poorly defined. In C. elegans , these include synaptonemal complex (SC) proteins, the Zip3 homologs ZHP-1-4, the MutSγ complex (MSH-4/5), and the CDK-2/COSA-1 complex. To probe the CO protein network, we applied TurboID-based proximity labeling coupled with mass spectrometry to three central CO factors: COSA-1, ZHP-3, and MSH-5. This analysis identified RMH-1, the C. elegans ortholog of RMI1 and a BTR complex subunit, as a shared interactor of all three. Structural predictions using AlphaFold3 and sequence conservation analysis highlighted four phenylalanine residues in the disordered region of ZHP-3 as likely mediators of the RMH-1:ZHP-3 interface. Mutations at these sites disrupt the timely repair of meiotic DNA double-strand breaks and proper chromosome segregation during meiosis, underscoring their functional importance. Ongoing studies are characterizing this interaction and its impact on CO formation. TurboID profiling also implicated the SC protein SYP-4 as a proximal interactor of ZHP-3. While previous genetic studies showed that the disordered C-terminal region of SYP-4 regulates CO patterning, the molecular basis for SC engagement with CO factors remained unknown. Our findings provide the first proteomic evidence linking SYP-4 to ZHP-3, nominating SYP-4 as a candidate mediator of the SC-CO interface. Biochemical assays are underway to determine whether this proximity reflects a direct physical interaction. Together, these approaches highlight new molecular connections among CO factors and suggest SYP-4 as a candidate mediator linking them to the SC.