Meiosis-specific functions of kinetochore protein SPC105R required for chromosome segregation in Drosophila oocytes

The reductional division of meiosis I requires the separation of chromosome pairs towards opposite poles. We have previously implicated the outer kinetochore protein SPC105R/KNL1 in driving meiosis I chromosome segregation through lateral attachments to microtubules and co-orientation of sister centromeres. To identify the domains of SPC105R that are critical for meiotic chromosome segregation, an RNAi-resistant gene expression system was developed. We found that SPC105Rs C-terminal domain (aa 1284-1960) is necessary and sufficient for recruiting NDC80 to the kinetochore and building the outer kinetochore. Furthermore, the C-terminal domain recruits BUBR1, which in turn recruits the cohesion protection proteins MEI-S332 and PP2A. Of the remaining 1283 amino acids, we found the first 473 are most important for meiosis. The first 123 amino acids of the N-terminal half of SPC105R contain the conserved SLRK and RISF motifs that are targets of PP1 and Aurora B kinase and are most important for regulating the stability of microtubule attachments and maintaining metaphase I arrest. The region between amino acids 124 and 473 are required for two activities that are critical for accurate chromosome segregation in meiosis I, lateral microtubule attachments and bi-orientation of homologs. Significance StatementO_LIKinetochore proteins regulate meiosis specific functions. SPC105R is a central regulator of kinetochore function but its role in meiosis is not well understood. C_LIO_LIWe identified regions of SPC105R that regulate key meiosis I functions, including fusing sister centromeres and the way the kinetochore interacts with the microtubules. C_LIO_LISPC105R is a hub that recruits several proteins to regulate kinetochore activity. Future work will involve identifying the proteins recruited by SPC105R that mediate these functions in meiosis. C_LI