Involvement of CTCF-Mediated Chromatin Loop Structure in Transcription of Clustered G1 Genes after Mitosis

In mammalian cells, transcription is globally silenced during mitosis owing to the highly-condensed chromatin. Immediately after mitosis, daughter cells restart the transcription of early G1 genes along the program which is transmitted from parental cells. Although several mechanisms (such as “mitotic gene bookmarking”) have been postulated, the detailed mechanism of transcription of early G1 genes is still unknown. Recently, we have identified 298 genes as the early G1 genes by a genome-wide analysis using nascent mRNA, and found that neighboring genes of early G1 genes are frequently up-regulated at G1 phase subsequent to transcription of the early G1 genes. It has been shown that chromatin loop structure is involved in transcription of clustered genes. Here, we show that CTCF-mediated chromatin loop structure around early G1 gene loci is retained from interphase to mitosis. The retained chromatin loop structure allows G1 genes, which are located nearby the early G1 gene loci, to be three-dimensionally in close proximity to one another and facilitates transcription of these genes in G1 phase. Furthermore, down-regulation of CTCF causes delay of M/ G1 transition and decreased transcription of early G1 and G1 genes. Our findings may provide a new insight into the mitotic transmission of transcriptional program to the daughter cells.