Topoisomerase I (TOP1) is a functional mitotic interactor of the bookmarking factor HNF1B

HNF1B (Hepatocyte Nuclear Factor 1-Beta) is a POU-homeobox transcription factor expressed in kidney and frequently mutated in patients suffering from Congenital Anomalies of the Kidney and the Urinary Tract (CAKUT). HNF1B is a bookmarking factor, able to bind mitotic chromatin and necessary for the post-mitotic reactivation of gene expression. In order to characterize the molecular functions of HNF1B as a bookmarking factor, we performed ChIPseq on asynchronous and mitotic renal cells. We developed a novel ChIP method with a non-aqueous crosslinking (NAQC) to circumvent the well-known artefactual effects of formaldehyde crosslinking of mitotic chromosomes. NAQC-ChIP allowed the retention of the mitotic signal that was lost with a regular ChIP. With this novel methodology, we show that the vast majority HNF1B binding sites detected in asynchronous cells are also bound in mitosis. ATACseq was performed in asynchronous and mitotic KEC cells.