Alpha-satellite RNA transcripts are repressed by centromere-nucleolus associations

Abstract

Centromeres play a fundamental role in chromosome segregation. Although originally thought to be silent chromosomal regions, centromeres are actively transcribed. However, the behavior and contributions of centromere-derived RNAs have remained unclear. Here, we used single-molecule fluorescence in-situ hybridization (smFISH) to detect alpha-satellite RNA transcripts in intact human cells. We find that alpha-satellite RNA smFISH foci fluctuate in their levels over the cell cycle and do not remain associated with centromeres, displaying localization consistent with other long non-coding RNAs. Our results demonstrate that alpha-satellite expression occurs through RNA Polymerase II-dependent transcription, but does not require centromere proteins and other cell division components. Instead, our work implicates centromere-nucleolar associations as the major factor regulating alpha-satellite expression. The fraction of nucleolar-localized centromeres inversely correlates with alpha-satellite transcripts levels, explaining variations in alpha-satellite RNA between cell lines. In addition, alpha-satellite transcript levels increase substantially when the nucleolus is disrupted. Together, our results are inconsistent with a direct, physical role for alpha-satellite transcripts in cell division processes, and instead support a role for ongoing transcription in promoting centromere chromatin dynamics. The control of alpha-satellite transcription by centromere-nucleolar contacts provides a mechanism to modulate centromere transcription and chromatin dynamics across diverse cell states and conditions.