Collaborative homologous pairing during C. elegans meiosis

Abstract

In preparation for meiotic chromosome segregation, homologous chromosomes need to pair, synapse (i.e., assemble the synaptonemal complex, SC), and then recombine to generate a physical linkage (i.e., chiasma) between them. In many organisms meiotic pairing capacity distri- buted along the entire chromosome length supports presynaptic alignment. In con- trast, the prevailing model for C. elegans proposes that presynaptic homologous pairing is performed solely by a master pairing-site, the pairing center (PC). In this model, the remaining chromosomal regions (the non-PC regions) are not actively involved in presynaptic pairing, and the SC assembling from the PC aligns the homologous chromosomes along non- PC regions and holds them together. Our recent work, however, demonstrates that C. elegans chromosomes establish presy- naptic alignment along the entire chromo- some length, suggesting that the non-PC regions are also actively involved in the presynaptic pairing process. Furthermore, we have also discovered that the chromo- domain protein MRG-1 facilitates this presynaptic non-PC pairing. The pheno- type of the mrg-1mutant indicates that the PC and the non-PC collaborate in success- ful pairing and synapsis. Therefore, homo- logous pairing mechanisms in C. elegans possibly sharemore similarity with those in other organisms than previously thought. Here, we elaborate on these observations and discuss a hypothetical model for presynaptic pairing in C. elegans based on our novel findings.