Analysis of meiosis in <i>Pristionchus pacificus</i> reveals plasticity in homolog pairing and synapsis in the nematode lineage.

Abstract

Meiosis is conserved across eukaryotes yet varies in the details of its execution. Here we describe a new comparative model system for molecular analysis of meiosis, the nematode <i>Pristionchus pacificus</i>, a distant relative of the widely studied model organism <i>Caenorhabditis elegans. P. pacificus</i> shares many anatomical and other features that facilitate analysis of meiosis in <i>C. elegans</i>. However, while <i>C. elegans</i> has lost the meiosis-specific recombinase Dmc1 and evolved a recombination-independent mechanism to synapse its chromosomes, <i>P. pacificus</i> expresses both DMC-1 and RAD-51. We find that SPO-11 and DMC-1 are required for stable homolog pairing, synapsis, and crossover formation, while RAD-51 is dispensable for these key meiotic processes. RAD-51 and DMC-1 localize sequentially to chromosomes during meiotic prophase and show nonoverlapping functions. We also present a new genetic map for <i>P. pacificus</i> that reveals a crossover landscape very similar to that of <i>C. elegans</i>, despite marked divergence in the regulation of synapsis and crossing-over between these lineages.