![]() ![]() The surface ectoderm will form the epidermis, hair, nails, enamel of the teeth, lining of the mouth, exocrine glands, adenohypophysis, lens, cornea, etc. 1, 3 The ectoderm will further differentiate into surface ectoderm and neural ectoderm. 3 The pluripotent epiblast, with the plasticity to form all somatic cells of the body, will segregate via gastrulation into the ectodermal, mesodermal and endodermal germ cell lineages ( Figure 1). The hypoblast will form the other portion of the extra embryonic tissues/cells (extra embryonic endoderm, extra embryonic splanchnic mesoderm and Hofbauer cells). The inner cell mass will segregate into the hypoblast and the pluripotent epiblast. ![]() The trophoblast will segregate into cytotrophoblast and syncytiotrophoblast and eventually form the extra embryonic placental tissues. The blastocyst differentiates into an inner cell mass, trophoblast, and gametes. Further development leads to the formation of the blastocyst, a hollow sphere. Subsequent mitotic division from the 4-cell stage results in the formation of the morula, a solid ball of blastomeres ( Figure 2). Blastomeres appear to lose the capability to form an entire organism as development progresses to the 8-cell stage and beyond. This inherent ability to form an entire organism complete with placental membranes and gametes is present at least through the 4-cell stage embryo 4 and has been demonstrated experimentally in mice, rats, cows and rhesus monkeys 5–8 after transfer of single blastomere from 4-cell stage embryos into a suitable host. It has the potential to form a three-dimensional embryo, as well as the extra-embryonic supportive placental tissues necessary for fetal development and the haploid gametes. 2, 3 The totipotent zygote is a self-contained entity that can give rise to an entire organism capable of procreating its species. 276A:75-102, 2004.ĭevelopment in mammals involves syngamy (fusion) of two haploid gametes to form the zygote, a fused diploid totipotent cell. Reprinted with permission from HE Young, AC Black JR. Keywords: Pluripotent stem cells, Somatic cells, Transplantation Abbreviationsįigure 1 Lineage Map of unidirectional cell differentiation during embryonic development from zygote to differentiated parenchyma and stroma. This review outlines the developmental process and differentiative capabilities of endogenous pluripotent stem cells the manufacture and differentiative capabilities of reprogrammed Pluripotent stem cells and the inherent characteristics of endogenous and reprogrammed Pluripotent stem cells. Reprogrammed Pluripotent stem cells are derived by either somatic cell nuclear transfer (SCNT) whereby there is the transfer of the nucleus from a differentiated cell into the cytoplasm of an enucleated oocyte or by the insertion of specific genes into terminally differentiated cells to artificially induce them to express attributes of more primitive pluripotent stem cells (induced Pluripotent stem cells, iPSCs). There are two subcategories of endogenous Pluripotent stem cells, embryonic stem cells (ESCs) and postnatal (“adult”) stem cells (ASCs). Endogenous Pluripotent stem cells are formed during development. There are two general categories of Pluripotent stem cells, endogenous Pluripotent stem cells and reprogrammed Pluripotent stem cells.
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