Tissues Derived From Embryonic Germ Layers

Embryonic epithelium called germ layer is a group of cells formed during animal embryogenesis. There are few primordial animals derived from the two germ layers, endoderm and ectoderm, most of the animals are derived from three germ layers, ectoderm, mesoderm and endoderm. The germ layer is called the main layer of animal embryo cells. As embryos grow, cells differentiate into various body tissues. In 1817, Christian Panda discovered three primitive germ layers when studying chicken embryos.

Embryonic germ cells are derived from primitive germline cells of early fetal tissues. Unlike embryonic stem cells, animal experiments using embryonic germ cells are limited. Isolation, culture and partial characterization of germ cells from human tissue gland ridges resulting from the use of the suspension was reported in 1998 (41). Although data from animal embryonic germ cell experiments are less than data from ES cell experiments, embryonic germ cells proceed further during development (5 to 9 weeks), so the potential range of fate is compared to ES cells It is generally thought that it is relatively limited. Although fetal tissue can provide targeted progenitor cells, the feasibility of large-scale procurement and manufacture of products utilizing such cells is questionable.

There are two kinds of stem cells, embryo and non-embryo. Since embryonic stem cells (embryonic stem cells) are totipotent, they can differentiate into all three embryonic germ layers. On the other hand, non-embryonic stem cells (non-embryonic stem cells), also called adult stem cells, are only pluripotent, and the possibility of differentiation into various cell types seems to be more restricted (11). Embryonic stem cells are derived from the inner cell mass of blastocysts (very early embryos), and adult stem cells are derived from mature tissue. In regenerative medicine, various kinds of cells, such as adult cells, endogenous tissue-specific stem cells, bone marrow stem cells, embryonic stem cells (12), epithelial pluripotent stem cells from adult / adult cells (iPS) It is used. 13)