Analysis of synaptonemal complex initiation. Mercedes R. Gyuricza¹, Kathryn B. Landy¹, Sanese K. White- Brown², Kim S. McKim¹. 1) Waksman Institute, Rutgers University, NJ; 2) UMDNJ, Piscataway, NJ.

   Accurate chromosome segregation is essential for proper production of gametes during meiosis, and requires both synapsis to hold homologous chromosomes together and cohesion to hold sister chromatids together. Synapsis is the process by which a proteinaceous structure, known as the synaptonemal complex (SC), is assembled between homologous chromosomes along the chromosome axis. The chromosome axis is composed of several proteins including both SC and cohesion proteins. We have found that SC formation is dependent upon cohesion proteins found at the axis, SMC1 and SMC3. However, when cohesion protein Rad21 is knocked-down, no effect is seen on the SC. We are looking into how other cohesion regulators effect the formation of the SC as well. Synapsis has been shown to initiate first at the centromere, and then at 6-8 sites on the chromosome arms. To test if the synapsis initiation sites correlate with cross over sites, we have examined two Drosophila homologs of the budding yeast cross over protein Zip3, CG31053 and CG12200. Our genetic evidence shows that both of these proteins are acting redundantly. Upon expression of CG12200 RNAi in a CG31053 mutant background, non-disjunction levels were increased and crossing over reduced compared to either RNAi or mutant individually. We are currently creating an antibody to CG12200 to determine if it localizes to crossover sites and can serve as a future crossover marker in Drosophila.