A dynamic meiotic cohesin complex regulates synaptonemal complex assembly in Drosophila oocytes

There are two meiotic cohesin pathways that regulate synaptonemal complex (SC) assembly in Drosophila melanogaster. We previously proposed that the kleisin C(2)M, which is required for SC assembly, is the only meiosis-specific component of a complex that includes Stromalin (SA1), Nipped-B, SMC1 and SMC3. The C-terminal and N-terminal domains of C(2)M contain several conserved residues known to interact with SMC1 or SMC3 and form a ring structure in budding yeast. Our mutant analysis has shown that these conserved residues are critical for SC formation. These results suggest that C(2)M may require a ring structure to perform meiosis-specific functions such as the formation of SC, and that each domain has unique functions in SC assembly. We also show that SA1 colocalizes with and depends on C(2)M. However, C(2)M is more dynamic than SA1 or SMC1, and may regulate the dynamics and chromosome loading of SMC1 and SA1. Indeed, C(2)M induces SC assembly when ectopically expressed in germline mitotic cells. We propose that C(2)M specifies the meiotic SC assembly functions to the cohesin complex.