Characterization of cohesin subunit Scc3 in sister chromatid cohesion maintenance during meiosis 

Department of Biological Science, Florida State University, Tallahassee 32306

November 21, 2007

  Of all eukaryotes meiosis plays a central role in sexual reproduction. Accurate chromosome segregation during meiosis is critical for generating genetic diversity and producing progeny with normal chromosome numbers.  During meiosis, cells undergo one round of DNA replication followed by two rounds of chromosome segregation. In meiosis I, homologs pair, recombine, and then separate, while sister chromatids remain cohesive until meiosis II.  Sister chromatid cohesion is mediated by cohesin, a ring-shaped protein complex composed of Smc1, Smc3, Mcd1/Scc1/Rec8, and Scc3.  Sister chromatid cohesin is also required for generating a chromosome linkage that facilitates chromosome bi-orientation onto the microtubule spindle prior to homolog separation. My research is focused on elucidating the molecular mechanism by which cohesin regulates meiotic recombination and proper chromosome segregation during meiosis in the budding yeast, Saccharomyces cerevisiae. We have created a meiotic conditional allele of SCC3, which encodes the Scc3 subunit of the cohesin complex. This novel mutant allele allowed me to address Scc3’s role in meiotic cohesin regulation, which is poorly understood previously.  My preliminary studies show that Scc3 is required for chromosome segregation during yeast meiosis. I also found that Scc3 is possibly degraded earlier than Rec8, another subunit of cohesin whose cleavage was shown previously to govern cohesin removal from chromosomes.  This novel observation suggests a critical role of Scc3 in cohesin maintenance during meiosis. I plan to characterize further the role of Scc3 in cohesin maintenance by addressing the following questions: First, when and how is Scc3 degraded? Second, does Scc3 degradation affect Rec8 protection and/or cleavage? Third, what is the role of Scc3 in homolog recombination? By addressing these questions, it will give us a better view of Scc3 function in cohesin regulation and help elucidate the molecular mechanisms of recombination and chromosome segregation during meiosis.