Nuclear proteome analysis of undifferentiated mouse embryonic stem and germ cells

Embryonic stem cells (ESCs) and embryonic germ cells (EGCs) provide exciting models for understanding the underlying mechanisms that make a cell pluripotent. Indeed, such understanding would enable dedifferentiation and reprogrammation of any cell type from a patient needing a cell therapy treatment. Proteome analysis has emerged as an important technology for deciphering these biological processes and thereby ESC and EGC proteomes are increasingly studied. Nevertheless, their nuclear proteomes have only been poorly investigated up to now. In order to investigate signaling pathways potentially involved in pluripotency, proteomic analyses have been performed on mouse ESC and EGC nuclear proteins. Nuclei from ESCs and EGCs at undifferentiated stage were purified by subcellular fractionation. After 2‐D separation, a subtractive strategy (subtracting culture environment contaminating spots) was applied and a comparison of ESC, (8.5 day post coïtum (dpc))‐EGC and (11.5 dpc)‐EGC specific nuclear proteomes was performed. A total of 33 ESC, 53 (8.5 dpc)‐EGC, and 36 (11.5 dpc)‐EGC spots were identified by MALDI‐TOF‐MS and/or nano‐LC‐MS/MS. This approach led to the identification of two isoforms (with and without N‐terminal acetylation) of a known pluripotency marker, namely developmental pluripotency associated 5 (DPPA5), which has never been identified before in 2‐D gel‐MS studies of ESCs and EGCs. Furthermore, we demonstrated the efficiency of our subtracting strategy, in association with a nuclear subfractionation by the identification of a new protein (protein arginine N‐methyltransferase 7; PRMT7) behaving as proteins involved in pluripotency.