How Does a Synaptonemal Complex Protein Promote Crossover Recombination and Synapsis?

Wesleyan University, Middletown CT

Investigators

Linked publications, trials & patents

Abstract

Project Summary Our proposed research aims to decipher the molecular mechanisms that underlie homologous chromosome segregation during reproductive cell formation. Meiosis is the specialized cell division cycle that partitions the two homologous copies of every chromosome (homologs) to separate daughter nuclei, effectively reducing chromosome ploidy. Errors in chromosome segregation lead to aneuploid reproductive cells carrying too many or two few chromosomes. Key to successful homolog segregation is the prior establishment of transient but stable linkages between replicated chromosomes; for most organisms these links are formed by interhomolog crossover recombination events, in conjunction with intact sister cohesion. How crossover events are efficiently generated between every chromosome pair during meiosis remains poorly understood, but for most organisms it is clear the process involves an exquisite coordination between large-scale chromosome movements and local DNA repair processes. A conserved multi-protein structure, the synaptonemal complex (SC), mediates an intimate alignment between homologous partner chromosome axes and forms the physical context in which DNA repair intermediates undergo maturation. SC has long been associated with successful crossover recombination, and although our research demonstrated that the SC structure per se is dispensable for crossing over in S. cerevisiae (budding yeast), we also showed that the SC structural component, Zip1, has a genetically separable function in promoting crossovers. Our structurefunction analysis reveals adjacent domains within Zip1 's N terminus that function independently to promote crossover recombination and SC assembly, potentially through separate but adjacent interactions with the procrossover E3 SUMO ligase, Zip3, and the SC central element protein complex Ecm11-Gmc2. Our research over the past two years has i) obtained additional evidence for an intriguing phosphorylationbased switch mechanism that controls Zip1's crossover and SC assembly activities, ii) revealed noncontiguous regions of Zip1 that phenocopy one another in a manner that suggests a specific overlapping configuration of Zip1 within mature SC, iii) discovered Zip1 protects Zip3 from proteosome-mediated degradation, iv) corrected Zip3's translational start site, and v) developed proximity labeling as a tool to both study interactions between pro-crossover and SC proteins and to identify new proximity targets of crossover and synapsis proteins. Experiments proposed in this renewal application support a rich training environment for one doctoral student and several undergraduates and use a cost-effective organism with powerful molecular genetics accessible to students at all levels. The proposed Aims build upon recent data and are designed to deepen our understanding of how Zip1 's N terminus collaborates with other factors, particularly the Zip3 SUMO ligase, to promote crossover recombination, and how Zip1 's pro-crossover activity is properly coordinated with and coupled to assembly of the supramolecular SC structure, which also requires Zip1 as a building block.