| Ectomesenchyme was an unique structure of vertebrates embryo composed of postmigratory cephalic neural crest cell (NCC) and its derivatives. Cephalic NCC was though have the highest potentency, the special feature of which is its ability to produce dual neural and mesenchymal lineage derivatives. Works of many years performed in avian and mammalian system both in vivo and in vitro, mainly at cellular level, had clearly described a neural crest-ectomesenchyme-cranioface developmental pattern in head and face genesis.During development , cephalic NCC undergo three primary developmental events: migration from the rhombomeric neuroectoderm to the pharyngeal arches, proliferation as the ectomesenchyme within the arches, and development to various terminate structures of head and face. Migrating crest cells interact with surrounding cells and undergo an epithelium to mesenchymal phenotype transition. It had been proposed that ectomesenchymal precursors diverged from the other precursors at the premigratory stage. Furthermore, both in vivo and in vitro works had demonstrated that NCC underwent progressively restriction. However,Baroffio et al showed that 2.6% of migrating cephalic NCCs consisting of precursors were able to produce dual neural and mesenchymal lineage derivatives, suggesting that migrating cells still contains pluripotent cephalic NCSC. Whether such undifferentiated NCSC still persist in its derived ectomesenchyme after end of migration were unknown. The fact that neural crest was a transit structure, and that various types of craniofacial structures directly develop from ectomesenchyme, suggesting which also was a multipotent structure, like neural crest. Therefore, we believed that ectomesenchyme contained undifferentiated NCSCs or its transited stem cells.The facts that stem cells existed in ectomesenchyme were supported by some outstanding works. For example, the direct proof was the finding of dental pulp stem cell(DPSC). DPSC was located in postnatal dental pulp tissue, which indeed derived from ectomesenchyme. Transplantation of dental pulp mesenchymal cells into immunocomprised mouse leaded to formation of a dentin/pulp-like complex. DPSCs also had capacity to produce odontoblasts and adiopcytes, although self-renewal was not detected. Related studies had provided evidence that neural crest stem cell(NCSC) still persisted in its postmigratory derivatives after end of migration. In some case, such stem cells were observed undergoing immediately phenotype changes; but in PNS, such stem cells were concluded still persisting by undergoing self-renewal in vivo. Moreover, by long-term culture of blood cells, Labit et al showed adult human blood contained multipotent precursors derived from ectomesenchyme, suggesting the longevity of EMSC. Although, there were so many evidences indicate the existence of EMSC, which have not been identified and isolated.The aim of the present study was to identify and isolate the ectomesenchyme stem cells and to demonstrate that EMSC have the character of plasticity both in vivo and in vitro. 1 Identify the phenotype of ectomesenchymal cell 1.1 Study on the morphology of ectomesenchymal cellThe primary ectomesenchymal cells of E 12.5 SD fetal mandibular process were isolated. Electric microscope was used to identify the characteristics of cells. Electric microscope showed that most of those cells looked like mesenchymal cells; The morphology of these cells were irregular, astroid or fusiform mainly with processes, The ratio of nucleolus and cytolymph was high, The cell often had obvious and big nucleolus and had many Altmann's granules. The data of electric microscope suggested that most of ectomesenchymal cell maintained undifferentiated and active status. 1.2 Identify the phenotype of ectomesenchymal cellEctomesenchymal tissue cells were detected by immunohistochemistry The staining of tissue sections showed that most of facial mesenchymal-like cells expressed S-100, Vimtine, a-SMA, but not expressed any terminate markers, such as perpher...
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