RESUMO
As cells enter mitosis, the genome is restructured to facilitate chromosome segregation, accompanied by dramatic changes in gene expression. However, the mechanisms that underlie mitotic transcriptional regulation are unclear. In contrast to transcribed genes, centromere regions retain transcriptionally active RNA polymerase II (Pol II) in mitosis. Here, we demonstrate that chromatin-bound cohesin is necessary to retain elongating Pol II at centromeres. We find that WAPL-mediated removal of cohesin from chromosome arms during prophase is required for the dissociation of Pol II and nascent transcripts, and failure of this process dramatically alters mitotic gene expression. Removal of cohesin/Pol II from chromosome arms in prophase is important for accurate chromosome segregation and normal activation of gene expression in G1. We propose that prophase cohesin removal is a key step in reprogramming gene expression as cells transition from G2 through mitosis to G1.
Assuntos
Proteínas de Ciclo Celular/fisiologia , Proteínas Cromossômicas não Histona/fisiologia , Regulação da Expressão Gênica , Mitose/genética , Transcrição Gênica , Anáfase/genética , Animais , Aurora Quinase B/análise , Ciclo Celular , Proteínas de Ciclo Celular/análise , Linhagem Celular , Centrômero/enzimologia , Segregação de Cromossomos , Fase G1/genética , Pontos de Checagem da Fase G2 do Ciclo Celular/genética , Humanos , Metáfase/genética , Prófase , RNA Polimerase II/metabolismo , Xenopus laevis , CoesinasRESUMO
Mitotic chromatin is largely assumed incompatible with transcription due to changes in the transcription machinery and chromosome architecture. However, the mechanisms of mitotic transcriptional inactivation and their interplay with chromosome assembly remain largely unknown. By monitoring ongoing transcription in Drosophila early embryos, we reveal that eviction of nascent mRNAs from mitotic chromatin occurs after substantial chromosome compaction and is not promoted by condensin I. Instead, we show that the timely removal of transcripts from mitotic chromatin is driven by the SNF2 helicase-like protein Lodestar (Lds), identified here as a modulator of sister chromatid cohesion defects. In addition to the eviction of nascent transcripts, we uncover that Lds cooperates with Topoisomerase 2 to ensure efficient sister chromatid resolution and mitotic fidelity. We conclude that the removal of nascent transcripts upon mitotic entry is not a passive consequence of cell cycle progression and/or chromosome compaction but occurs via dedicated mechanisms with functional parallelisms to sister chromatid resolution.