A Dynamic Mode of Mitotic Bookmarking by Transcription Factors

Abstract

SummaryDuring mitosis, transcription is shut off, chromatin condenses, and most transcription factors (TFs) are reported to be excluded from chromosomes. How do daughter cells re-establish the original transcription program? Recent discoveries that a select set of TFs remain bound on mitotic chromosomes suggest a potential mechanism for maintaining transcriptional programs through the cell cycle termed mitotic bookmarking. Here we report instead that many TFs remain associated with chromosomes, and that the exclusion previously described is largely a fixation artifact. In particular, most TFs we tested are significantly enriched on mitotic chromosomes. Studies with Sox2 reveal that this mitotic interaction is more dynamic than in interphase and requires both DNA binding and nuclear import. Furthermore, this dynamic mode results from lack of transcriptional activation rather than decreased accessibility of underlying DNA sequences in mitosis. The nature of the cross-linking artifact prompts careful re-examination of the role of TFs in mitotic bookmarking. Highlights• Many transcription factors bind to mitotic chromosomes • Sox2 mitotic interaction is dynamic and requires DNA binding and nuclear import• DNA remains highly accessible in mitotic chromosomes• Formaldehyde-based cross-linking leads to mis-localization of TFs peer-reviewed)

Pioneer transcription factors shape the epigenetic landscape

“…Both specific and non-specific binding sites on mitotic chromosomes were also observed for FoxA1 (77) where specific FoxA1 binding occurs at 15% of its interphase targets. Recently, Sox2 and Oct4 were also shown to remain bound during mitosis (78,79). In this last study, the authors also show using live imaging techniques that crosslinking with formaldehyde leads to eviction of most TFs from mitotic chromosomes.…”

Widespread Mitotic Bookmarking by Histone Marks and Transcription Factors in Pluripotent Stem Cells

“…Among them, OCT4, SOX2, ESRRB and KLF4 have been reported to also function as pioneer factors (Iwafuchi-Doi and Zaret, 2014; Soufi et al, 2012; Soufi et al, 2015), sharing critical properties with known bookmarking TFs. However, evidence for a potential bookmarking role for some of these TFs has only recently begun to emerge (Festuccia et al, 2016; Teves et al, 2016; Deluz et al, 2016). Similarly, although the functional genomic elements that control stem cell identity and the histone marks that decorate them are well characterized (Hawkins et al, 2010; Mikkelsen et al, 2007; Whyte et al, 2013), their status during mitosis remains unknown.…”

Mitotic transcription and waves of gene reactivation during mitotic exit

“…However, the dynamic range of antibody-based methods is much less than from direct measurements of nascent transcription and crosslinking artifactually causes protein exclusion from mitotic chromatin (14, 18). Transcription elongation inhibition of prometaphase HeLa cells elicits paused RNAP2 at promoters, suggesting the presence of elongating enzyme, even though elongating RNAP2 was not detected directly (19).…”