Exploring SOLO Working Mechanism in Drosophila Meiosis Cohesin Complex. Qian Ma, Bruce McKee. Univ of Tennessee, Knoxville, Knoxville, TN.

   In eukaryotes, sister chromatids are closely aligned due to cohesion, a process essential for chromosome pairing and segregation during both mitosis and meiosis. Chromatid missegregation and mutation of cohesion proteins are associated with cancers, infertility, Down syndrome, and Cornelia de Lange Syndrome (CdLS). A conserved cohesin complex in a ring structure is composed of four subunits, including each of these four members or their homologs, SMC1, SMC3, SCC1/RAD21/REC8, and SCC3/SA. However, it is still unclear either the complex components or the working mechanism in Drosophila meiosis cohesion. Sisters on the loose (SOLO) is a newly reported meiotic protein required for centromere cohesion, and cohesin complex localization by recruiting cohesin subunit SMC1 in Drosophila meiosis. Our study utilized site-directed mutagenesis to carry out structure-function analysis of SOLO. Sequence alignment indicates SOLO shares conserved C terminal residues with SCC1/RAD21/REC8 family members, which are important for their interactions with SMC1 in cohesin complex. To test whether SOLO C terminus residues work similarly as SCC1/RAD21/REC8, by interacting with SMC1, we designed a series of mutations at the SOLO C terminal conserved residues using the Invitrogen Gateway system. With C terminus conserved residue mutations, SOLO localization is disrupted, and accurate chromosome segregation is compromised during meiosis in both males and females. In addition, we found centromere pairing is disrupted in SOLO C terminus mutant flies during meiosis. Furthermore, Yeast-Two-Hybrid was performed in order to test the direct interactions between SOLO, specifically N and C terminus domains, and cohesin proteins, SMC1 and SMC3. We found SOLO interacts with SMC1 with its C terminus domain while interacting with SMC3 by its N terminus domain, from both yeast growth and -Galactosidase assay. These results support the idea that SOLO works as the SCC1/Rec8 homolog in Drosophila meiosis cohesin complex.