Global inhibition of deadenylation stabilizes the transcriptome in mitotic cells

In the presence of cell division errors, mammalian cells can pause in mitosis for tens of hours with little to no transcription, while still requiring continued translation for viability. These unique aspects of mitosis require substantial adaptations to the core gene expression programs. Indeed, during interphase, the homeostatic control of mRNA levels involves a constant balance of transcription and degradation, with a median mRNA half-life of ~2-4 hours. If such short mRNA half-lives persisted in mitosis, cells would be expected to quickly deplete their transcriptome in the absence of new transcription. Here, we report that the transcriptome is globally stabilized during prolonged mitotic delays. Typical mRNA half-lives are increased >4-fold in mitosis compared to interphase, thereby buffering mRNA levels in the absence of new synthesis. Moreover, the poly(A)-tail-length profile of mRNAs changes in mitosis, strongly suggesting a mitotic repression of deadenylation. We further show that mRNA stabilization in mitosis is dependent on cytoplasmic poly(A)-binding proteins PABPC1&4. Depletion of PABPC1&4 disrupts the maintenance of mitotic arrest, highlighting the critical physiological role of mitotic transcriptome buffering.