Determinants of minor satellite RNA function in chromosome segregation in mouse embryonic stem cells

Centromeric DNA regions are highly diverse and evolve rapidly. Chen et al. investigate how the correct balance of centromeric transcripts from mouse stem cells affects chromatin recruitment of CENPC and propose a model where structural RNA features, rather than sequence motifs, are key for RNA-protein interactions. The centromere is a fundamental higher-order structure in chromosomes ensuring their faithful segregation upon cell division. Centromeric transcripts have been described in several species and suggested to participate in centromere function. However, low sequence conservation of centromeric repeats appears inconsistent with a role in recruiting highly conserved centromeric proteins. Here, we hypothesized that centromeric transcripts may function through a secondary structure rather than sequence conservation. Using mouse embryonic stem cells (ESCs), we show that an imbalance in the levels of forward or reverse minor satellite (MinSat) transcripts leads to severe chromosome segregation defects. We further show that MinSat RNA adopts a stem-loop secondary structure, which is conserved in human alpha-satellite transcripts. We identify an RNA binding region in CENPC and demonstrate that MinSat transcripts function through the structured region of the RNA. Importantly, mutants that disrupt MinSat secondary structure do not cause segregation defects. We propose that the conserved role of centromeric transcripts relies on their secondary RNA structure.