![]() ![]() This specification is accompanied by extensive epigenetic reprogramming that involves global DNA demethylation, chromatin reorganization and imprint erasure leading to totipotency. In the mouse, primordial germ cells are specified from epiblast cells. While the cuboidal hypoblast cells delaminate ventrally, away from the embryonic pole, to line the blastocoele, the remaining cells of the inner cell mass, situated between the hypoblast and the polar trophoblast, become the epiblast and comprise columnar cells. In mammalian embryogenesis, differentiation and segregation of cells composing the inner cell mass of the blastocyst yields two distinct layers-the epiblast ("primitive ectoderm") and the hypoblast ("primitive endoderm"). Other early embryologists that studied the epiblast and blastoderm include Karl Ernst von Baer (1792-1876) and Wilhelm His (1831-1904). He published these findings in Beiträge zur Entwickelungsgeschichte des Hühnchens im Eye. With the help of anatomist Ignaz Döllinger (1770–1841) and draftsman Eduard Joseph d'Alton (1772-1840), Pander observed thousands of chicken eggs under a microscope, and ultimately discovered and described the chicken blastoderm and its structures, including the epiblast. The epiblast was first discovered by Christian Heinrich Pander (1794-1865), a Baltic German biologist and embryologist. The other layer of the inner cell mass, the hypoblast, gives rise to the yolk sac, which in turn gives rise to the chorion. The amnionic ectoderm and extraembryonic mesoderm also originate from the epiblast. It derives the embryo proper through its differentiation into the three primary germ layers, ectoderm, mesoderm and endoderm, during gastrulation. In amniote embryonic development, the epiblast (also known as the primitive ectoderm) is one of two distinct cell layers arising from the inner cell mass in the mammalian blastocyst, or from the blastula in reptiles and birds, the other layer is the hypoblast. ![]()
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