RESUMO
OBJECTIVE@#To understand the differentiation of mesoderm-derived Flk1 cells on different locations of the early mouse embryonic development and to explore the potential of Flk1 cells to differentiate into mesenchymal lineage, like pericytes during vascular development.@*METHODS@#Based on the Cre-LoxP system conditional knockout study strategy, the Flk1-Cre mice and ROSA26 reporter mice were used for lineage-tracing studies. The fate of the Flk1 progenitor cells was traced with the GFP population. The detection of mesoderm marker Flk1, hematopoietic cell-specific marker CD45, endothelial cell-specific markers CD31, CD144, and Emcn (endomucin), pericyte specific markers PDGFRβ and NG2, using the methods of immunohistochemistry, immunofluorescence, and flow cytometry should be combined to solve the concerned problems.@*RESULTS@#Immunohistochemical staining of different fractions of E8.5-10.5 in the early embryogenesis of Flk1-Cre; ROSA26-EYFP mouse lineage showed that there were multiple populations in the Flk1 cell-derived GFP population surrounding hematopoietic sites, such as dorsal aortas, limb buds and yolk sac. In addition to hematopoietic cells, the CD31/Emcn typical endothelial cells distributed specifically along the blood vessel wall, there were many types of cell populations, such as mesenchymal-like cells. The immunofluorescence demonstrated that the cells of this group are neither hematopoietic, non-endothelial cells around the blood vessels, which are NG2+ pericytes. FACS analysis also confirmed that Flk1 cells contributed to pericytes. In addition, in different hematopoietic sites of the embryo, a small population of CD31+CD140B+ cell populations with a mesenchymal-like morphology was observed in the GFP population.@*CONCLUSION@#In the early stages of embryogenesis, mesoderm-derived Flk1 populations not only contribute to hematopoietic, endothelial, and muscle lineages, but also have a differentiation potential for mesenchymal lineage, like pericytes. The presumably observed CD31CD140B cell population may be a group of endothelial cells differentiated from Flk1 progenitor cells and undergoing an endothelium-to-mesenchymal transition, EndMT, gradually losing the endothelial surface-specific marker and also starting to express a pericyte surface-specific marker.