Mouse HORMAD1 and HORMAD2, Two Conserved Meiotic Chromosomal Proteins, Are Depleted from Synapsed Chromosome Axes with the Help of TRIP13 AAA-ATPase

Abstract

Meiotic crossovers are produced when programmed double-strand breaks (DSBs) are repaired by recombination from homologous chromosomes (homologues). In a wide variety of organisms, meiotic HORMA-domain proteins are required to direct DSB repair towards homologues. This inter-homologue bias is required for efficient homology search, homologue alignment, and crossover formation. HORMA-domain proteins are also implicated in other processes related to crossover formation, including DSB formation, inhibition of promiscuous formation of the synaptonemal complex (SC), and the meiotic prophase checkpoint that monitors both DSB processing and SCs. We examined the behavior of two previously uncharacterized meiosis-specific mouse HORMA-domain proteins—HORMAD1 and HORMAD2—in wild-type mice and in mutants defective in DSB processing or SC formation. HORMADs are preferentially associated with unsynapsed chromosome axes throughout meiotic prophase. We observe a strong negative correlation between SC formation and presence of HORMADs on axes, and a positive correlation between the presumptive sites of high checkpoint-kinase ATR activity and hyper-accumulation of HORMADs on axes. HORMADs are not depleted from chromosomes in mutants that lack SCs. In contrast, DSB formation and DSB repair are not absolutely required for depletion of HORMADs from synapsed axes. A simple interpretation of these findings is that SC formation directly or indirectly promotes depletion of HORMADs from chromosome axes. We also find that TRIP13 protein is required for reciprocal distribution of HORMADs and the SYCP1/SC-component along chromosome axes. Similarities in mouse and budding yeast meiosis suggest that TRIP13/Pch2 proteins have a conserved role in establishing mutually exclusive HORMAD-rich and synapsed chromatin domains in both mouse and yeast. Taken together, our observations raise the possibility that involvement of meiotic HORMA-domain proteins in the regulation of homologue interactions is conserved in mammals.

Disassembly of mitotic checkpoint complexes by the joint action of the AAA-ATPase TRIP13 and p31 comet

“…Because the Cdc20-Mad2 substrate used in our assay contained p31 comet (necessary for the release of the subcomplex from MCC), TRIP13 seemed to be a likely candidate. Indeed, immunoblotting of MonoQ column fractions with anti-TRIP13 showed an exact coincidence of the peak of the elution of TRIP13 protein with that of Cdc20-Mad2 dissociating activity, with both centered in fractions [25][26] (Fig. 1B).…”

“…In some instances, an AAA-ATPase can bind to different adaptor proteins, thus changing its substrate specificities and cellular functions (19). In the case of the TRIP13 AAA-ATPase and of its homologs, a role in meiotic recombination has been reported in mice, yeast, worms, and plants (25)(26)(27)(28). This function has been explained by their action to dislocate certain proteins from Recombinant Cdc20-Mad2 complex was expressed and purified as described in Materials and Methods and was added to the assay at 2 nM.…”

“…2A. chromatin (26)(27)(28). A different function of TRIP13 has been suggested by a proteomic data mining study that identified it as a kinetochore protein that interacts with p31 comet (16).…”

Evolutionary history of the mammalian synaptonemal complex

“…A third organizational axes layer is made by the HORMA-domain proteins HORMAD1 and HORMAD2. They preferentially bind to unsynapsed chromosome axes and become displaced from the AEs by synapsis formation in a TRIP13-dependent manner (Wojtasz et al 2009). A Hormad1 -/-mutant mouse model suggests that the HORMADs function in a meiotic "synapsis" checkpoint.…”

Meiotic double strand breaks repair in sexually reproducing eukaryotes: We are not all equal

“…Recently a Pch2 orthologue (TRIP13) has also been identified in mice. The analyses of these mutants revealed that TRIP13 is required for the removal of HORMAD1 from synapsed axes [34], completed homologous synapses, and DSB repair, indicating that at least some of the functions of Pch2 are conserved in mammals. However a specific role in inter-homolog vs. sister bias has not been ascertained [35].…”