Oocyte Specific Homeobox 1 (Obox1) Facilitates Somatic Cell Reprogramming by Promoting Mesenchymal-to-Epithelial Transition and Mitigating Cell Hyper-proliferation

Mammalian oocytes possess fascinating unknown factors, which can reprogram terminally differentiated germ cells (sperm) or somatic cells into totipotent embryos. Here, we demonstrate that oocyte specific homeobox 1 (Obox1), an oocyte-specific factor, can markedly enhance the generation of induced pluripotent stem cells (iPSCs) from mouse fibroblasts in a proliferation-independent manner and can replace Sox2 to achieve pluripotency. Overexpression of Obox1 can greatly promote mesenchymal-to-epithelial transition (MET) at early stage of OSKM-induced somatic cell reprogramming and meanwhile, the cell hyper-proliferation can be significantly slowed down. Subsequently, the proportion of Thy1 negative cells and Oct4-GFP positive cells increased dramatically. Further analysis of gene expression and targets of Obox1 during reprogramming indicates that the expression of Obox1 can promote epithelial genes expression and repress cell cycle-related genes expression. Taken together, we conclude that the oocyte-specific factor Obox1 serves as a strong activator for somatic cell reprogramming through promoting the MET and mitigating cells hyper-proliferation. The reprogrammable MEFs derived from the transgenic mice carrying the tetO-OSKM transgene and Oct4-GFP/Rosa26-M2rtTA were used in the experiments. The reprogrammable MEFs that were not induced with doxycycline were designated as “MEF” (control). The reprogrammable cells with or without Obox1’s overexpression were induced with doxycycline (1ug/ml) for 3 days. The cells were harvested and performed RNA sequencing (RNA-seq) and chromatin immunoprecipitation followed by sequencing (ChIP-seq).