The ZMM protein Zip4 directly couples meiotic crossover formation to synaptonemal complex assembly

Meiotic crossover recombination is triggered by the formation of programmed double strand breaks (DSBs) catalyzed by the conserved Spo11 protein. Only a subset of these DSBs are repaired as crossovers, promoted by a group of eight evolutionarily conserved proteins, named ZMM. The synaptonemal complex (SC) that assembles between homologous chromosomes is composed of two axial elements, from which chromatin loops emanate, held together by a central region, composed of the central element and a transverse filament protein. In budding yeast, crossover formation is functionally linked to the formation of the SC, but the underlying mechanism is unknown. Here we found that the SC central element protein, Ecm11, mainly localizes on both DSB sites and sites that attach chromatin loops to the chromosome axis, in a way that strictly requires the ZMM protein Zip4. We further show that Zip4 directly interacts with Ecm11 and that point mutants that specifically abolish the Zip4-Ecm11 interaction loose Ecm11 binding to chromosomes and exhibit defective SC assembly. Interestingly, SC assembly can be partially rescued by artificially tethering interaction-defective Ecm11 to Zip4. This direct connection that ensures SC assembly from CO sites could be a way for the meiotic cell to shut down further DSB formation once enough recombination sites have been selected for crossovers, thereby preventing excess crossovers. Finally, we found that the mammalian ortholog of Zip4, TEX11, interacts with the SC central element TEX12, raising the possibility that this may be a general mechanism. Overall design: 4 samples total: each comes from two independent replicates each of anti-FLAG ChIP in untagged, Ecm11-His6FLAG3, zip4? Ecm11-His6FLAG3 and zip1? Ecm11-His6FLAG3 S. cerevisiae cells at 5 h in meiosis combined with 10% of spike-in S. mikatae Ecm11-His6FLAG3 cells at 4h in meiosis