Partial Differentiation of Cellular Living State for Nutrient Gradient in Gastrula of Animal Development

It was suggested by Cai a theory that, in animals, the nutrient gradient differentiates the cellular living states to form the three germ layers of embryonic gastrula differential developing into three different subsequent fates, with the endoderm manifesting cellular living states in nutritious condition and giving rise to the epithelium of digestive and respiratory system; the ectoderm manifesting cellular living states of nutrient dependence and environmental effects, and developing to the nervous and epithelial tissues; the mesoderm lying between them and emerging to the muscle and adipose. In parallel, it also complied with the regulation of nutrients on various cultured stem cells. In this chapter, it is briefly reviewed such embryonic differentiation of three layers of gastrula and further highlights that the early embryonic cleavage partially differentiates the cellular living states to form the nutrient gradient for three layers of gastrula via partial differentiation of proliferative animal hemisphere and nutritious vegetal hemisphere in most animals, including the mammals, birds, Xenopus, zebrafish, snails, sea urchin, and so on, but instead via oocyte polarity and embryonic invagination in Drosophila. Therefore, it is the formed nutrient gradient of gastrula that is conserved in evolution.