SUN is required to maintain centromere cohesion and for proper chromosome segregation during meiosis in both male and female Drosophila melanogaster. Badri Krishnan¹, Sharon Thomas¹, Hirotsugu Yamada¹, Rihui Yan¹, Bruce McKee^1,2. 1) Biochemistry and Cellular and Molecular biology, University of Tennessee, Knoxville, TN; 2) Genome Science and Technology program, University of Tennessee, Knoxville, TN.

   Cohesion between sister chromatids is essential for connecting homologous chromosomes during meiosis I and sister centromeres during meiosis I and II. Sister chromatid cohesion at the centromere is also essential for mono-orientation and bi-orientation of sister centromeres during meiosis I and II respectively. In the absence of adequate understanding of the cohesin complex in Drosophila melanogaster, knowledge of meiotic cohesion and chromosome segregation is derived from studies of Drosophila specific cohesion genes like ord and solo. We have identified a novel gene called sun, sisters unbound, which is essential for proper chromosome segregation during meiosis in both male and female Drosophila melanogaster. We performed genetic crosses to determine the frequency of non-disjunction in sun mutants. In order to investigate the segregation pattern of chromosomes and the status of centromeric cohesion during meiosis in sun mutants, we used Fluorescent-In-Situ-Hybridization (FISH) and immunostaining. Finally, to determine the cellular localization of SUN protein, we created transgenic lines carrying a construct of sun with the fluorescent tag Venus. We found that sun mutants cause high frequencies of both homologous and sister chromatid non-disjunction (NDJ) in both sexes, loss of sister centromere orientation during meiosis I and II and disruption of centromeric cohesion by late prophase I. SUN protein co-localizes with CID (Centromere Identifier) to the centromeric region in spermatocytes until anaphase II and in oocytes during prophase I. Our study indicates that SUN at the centromere helps in maintaining sister centromere cohesion and establishing sister centromere orientation patterns during meiosis I and meiosis II.