ZHP-3 Acts at Crossovers to Couple Meiotic Recombination with Synaptonemal Complex Disassembly and Bivalent Formation in C. elegans

Abstract

Crossover recombination and the formation of chiasmata normally ensure the proper segregation of homologous chromosomes during the first meiotic division. zhp-3, the Caenorhabditis elegans ortholog of the budding yeast ZIP3 gene, is required for crossover recombination. We show that ZHP-3 protein localization is highly dynamic. At a key transition point in meiotic prophase, the protein shifts from along the length of the synaptonemal complex (SC) to an asymmetric localization on the SC and eventually becomes restricted to foci that mark crossover recombination events. A zhp-3::gfp transgene partially complements a null mutation and reveals a separation of function; although the fusion protein can promote nearly wild-type levels of recombination, aneuploidy among the progeny is high, indicating defects in meiotic chromosome segregation. The structure of bivalents is perturbed in this mutant, suggesting that the chromosome segregation defect results from an inability to properly remodel chromosomes in response to crossovers. smo-1 mutants exhibit phenotypes similar to zhp-3::gfp mutants at higher temperatures, and smo-1; zhp-3::gfp double mutants exhibit more severe meiotic defects than either single mutant, consistent with a role for SUMO in the process of SC disassembly and bivalent differentiation. We propose that coordination of crossover recombination with SC disassembly and bivalent formation reflects a conserved role of Zip3/ZHP-3 in coupling recombination with SC morphogenesis.

Pro-crossover factors regulate damage-dependent apoptosis in the Caenorhabditis elegans germ line

“…15 Worms carrying mutations in CO-promoting factors, such as him-14 (the C. elegans orthologue of Msh4; called msh-4 hereafter), msh-5, and zhp-3, show an abnormal accumulation of RAD-51 foci that are interpreted as unresolved recombination intermediates. 11,19 Surprisingly, despite the accumulation of recombination intermediates, msh-5 mutants do not exhibit increased apoptosis above the basal level observed in wild-type worms 8 (also shown in this study). Similarly, mice lacking Mlh1, a protein that is also required for CO formation and localizes to CO sites in late pachytene, do not exhibit apoptosis induction during meiotic prophase.…”

“…These foci are thought to mark the single CO that is formed in each homologue pair during C. elegans meiosis. Before becoming limited to the 'pro-CO focus', ZHP-3 is first observed forming stretches along chromosomes during pachytene, 11,12 whereas COSA-1 appears directly at the transition from mid-pachytene to late pachytene forming a single focus per chromosome pair. The function of COSA-1 is required for recruiting MSH-5 and ZHP-3 to designated CO sites and, correspondingly, COSA-1 foci are absent in msh-5 mutants.…”

Manipulation of Karyotype inCaenorhabditis elegansReveals Multiple Inputs Driving Pairwise Chromosome Synapsis During Meiosis

“…Interestingly, several factors have been shown previously to associate transiently with the SCs during pachytene progression with a dynamics dependent on meiotic recombination. These include the predicted SUMO-ligase ZHP-3, which first associates along the lengths of SCs and then redistributes to concentrate on smaller domains defined by the crossover sites (Jantsch et al 2004;Bhalla et al 2008) and the AAA+-ATPase PCH-2, which associates with the SCs during early-mid pachytene but is lost from the chromosomes at late pachytene in a crossover-dependent manner (Deshong et al 2014). The dynamic association of these factors with the SC may represent another reflection of the transition from one synapsis phase to another that we propose in our model.…”

RBX1 (RING Box Protein 1) E3 Ubiquitin Ligase Is Required for Genomic Integrity by Modulating DNA Replication Licensing Proteins

“…Adult worms were dissected, freeze-cracked, fixed with paraformaldehyde, and incubated with antibodies as described (23). Rabbit antibodies to C. elegans RAD-51 (Strategic Diagnostics, Inc.) at 1:5000 and Alexa 555-labeled secondary antibodies (Invitrogen) at 1:500 were used.…”