EPCs are believed to be derived from the bone marrow and to home to sites of neovascularization and neoendothelialization where they differentiate into ECs. This raises the possibility that ESP may have originated from bone marrow stromal cells. Pyriproxyfen Indeed, bone marrow-derived EPCs contribute to the formation of new blood vessels in human and mouse endometrium. Furthermore, bone-marrow derived cells give rise to uterine epithelial cells in humans and mice, although the identity of these cells remains unclear. Based on the present results, we speculate that ESP represents one such candidate population. In view of these findings, we here propose a single model for ESP-driven endometrial regeneration and establishment of endometriosis. In this model, ESP cells, perhaps ultimately derived from the bone marrow, mainly reside in vascular endothelial walls and/or perivascular regions. Importantly, these ESP cells are present not only in the basalis but also in the functionalis endometrium. These cells, therefore, might be contained within the sloughed Riboflavin endometrium shed at menstruation. They might then implant onto the surface of ectopic sites such as the peritoneum through retrograde menstruation. Furthermore, some of these functionalis layer-derived ESP cells might remain in the uterine cavity after menstruation and implant again onto the deconstructed eutopic endometrium. In both eutopic and ectopic implantation, endothelial ESPs might give rise to various endometrial cell components in the process of ESP-driven angiogenesis. Our eutopic reimplantation hypothesis does not contradict the current paradigm but rather provides an additional mechanism for endometrial regeneration. We describe previously that a certain type of cells in endometrium could migrate, invade, form chimeric vasculature in the host kidney of NOG mouse and establish the functional circulatory system. In terms of the ability to invade into kidney parenchyma, these cells could be SP cells.From this point, their ability may be crucial for establishment and development endometriosis, because the angiogenesis is absolutely required for maintenance of endometriotic lesion.