title: B-Myb is critical for proper DNA duplication during an unperturbed S phase in mouse embryonic stem cells.
abstract: A common feature of early embryo cells from the inner cell mass (ICM) and of ESCs is an absolute dependence on an atypical cell cycle in which the G1 phase is shortened to preserve their self-renewing and pluripotent nature. The transcription factor B-Myb has been attributed a role in proliferation, in particular during the G2/M phases of the cell cycle. Intriguingly, B-Myb levels in ICM/ESCs are greater than 100 times compared with those in normal proliferating cells, suggesting a particularly important function for this transcription factor in pluripotent stem cells. B-Myb is essential for embryo development beyond the preimplantation stage, but its role in ICM/ESCs remains unclear. Using a combination of mouse genetics, single DNA fiber analyses and high-resolution three-dimensional (3D) imaging, we demonstrate that B-Myb has no influence on the expression of pluripotency factors, but instead B-Myb ablation leads to stalling of replication forks and superactivation of replication factories that result in disorganization of the replication program and an increase in double-strand breaks. These effects are partly due to aberrant transcriptional regulation of cell cycle proliferation factors, namely c-Myc and FoxM1, which dictate normal S phase progression. We conclude that B-Myb acts crucially during the S phase in ESCs by facilitating proper progression of replication, thereby protecting the cells from genomic damage. Our findings have particular relevance in the light of the potential therapeutic application of ESCs and the need to maintain their genomic integrity.
authors: Institute of Biomedical Research, College of Medical and Dental Sciences, University of Birmingham, Edgbaston, Birmingham, United Kingdom.
authors: Maëlle
authors: M
authors: Lorvellec
authors: Stéphanie
authors: S
authors: Dumon
authors: Apolinar
authors: A
authors: Maya-Mendoza
authors: Dean
authors: D
authors: Jackson
authors: Jon
authors: J
authors: Frampton
authors: Paloma
authors: P
authors: García
mesh_terms: D000818:Animals; D015153:Blotting, Western; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D049109:Cell Proliferation; D047369:Chromatin Immunoprecipitation; D004261:DNA Replication / Q000235:genetics*; D053595:Embryonic Stem Cells / Q000166:cytology* / Q000378:metabolism*; D005434:Flow Cytometry; D005455:Fluorescent Antibody Technique; D000072278:Forkhead Box Protein M1; D051858:Forkhead Transcription Factors / Q000235:genetics / Q000378:metabolism; D007150:Immunohistochemistry; D051379:Mice; D018613:Microscopy, Confocal; D050814:Octamer Transcription Factor-3 / Q000235:genetics / Q000378:metabolism; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016196:S Phase / Q000235:genetics*; D055748:SOXB1 Transcription Factors / Q000235:genetics / Q000378:metabolism; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*
chemical_list: D018797:Cell Cycle Proteins; D000072278:Forkhead Box Protein M1; D051858:Forkhead Transcription Factors; C491524:Foxm1 protein, mouse; C499306:Mybl2 protein, mouse; C489428:Myc protein, mouse; D050814:Octamer Transcription Factor-3; D016271:Proto-Oncogene Proteins c-myc; D055748:SOXB1 Transcription Factors; D015534:Trans-Activators