Human centromere consists of repetitive sequences that generate non-coding (nc) RNAs. Satellite I (Sat I) RNA is one of ncRNAs transcribed from centromeres. To investigate functions of Sat I RNA, we carried out knockdown of Sat I RNA using anti-sense oligonucleotides. HeLa cells depleted of Sat I RNA showed a grape shape phenotype, the abnormal nuclear morphology caused by defective chromosome segregation. We found that Aurora B, a key factor of chromosome segregation, associates with Sat I RNA. Interestingly, in Sat I RNA-depleted cells, Aurora B showed elevated kinase activity and its mis-localization from centromeres, suggesting that Sat I RNA regulates chromosome segregation through the control of Aurora B function.

   Experiments using chromosome spreads revealed that depletion of Sat I RNA causes defective centromeric cohesion of sister chromatids. To investigate roles of Sat I RNA in centromeric cohesion, we examined proteins associated with Sat I RNA by purification of Sat I RNP, and identified RBMX as one of components of Sat I RNP. RBMX is known to associate with cohesin. Knockdown of RBMX caused defective chromosome segregation and chromatid cohesion. In addition, RBMX was dissociated from chromatin fraction in Sat I RNA-depleted cells.

   DEAH box helicase DHX38, one of pre-mRNA splicing factors, was reported to be a component of an interphase centromere complex in HeLa cell (Obuse et al. 2004). We found knockdown of DHX38 by RNAi induced the grape shape phenotype similar to cells depleted of Sat I RNA. Co-IP experiments using anti-DHX38 antibody revealed that DHX38 associates with Sat I RNA. Interestingly, association of DHX38 with Sat I RNA was observed only in interphase cells, not in M phase arrested cells. In contrast, Aurora B and RBMX were associated with Sat I RNA only in M phase cells. These results suggest that Sat I RNP is remodeled during progression of cell cycle.