Stem Cells & Wnt Signaling Paths (Stem Cells & Wnt)

Stem cells are the cells of origin. Stem cells are cells with the potential for proliferation and differentiation, and have the ability to self-renewing and produce highly differentiated functional cells. Stem cells have the following biological characteristics: 1 remain undifferentiated or poorly differentiated throughout life; 2 the number and position in the body are relatively constant; 3 has the ability to self-renew; 4 has unlimited division and proliferation; 5 has multi-directional differentiation potential, Differentiated into different types of tissue cells, adult stem cells such as hematopoietic stem cells, bone marrow mesenchymal stem cells, and neural stem cells have certain potentials for cross-system and even trans-embryonic differentiation; 6 slow periodicity of division, most stem cells are in G0 phase 7 splits in two ways, forming two identical stem cells for the split and asymmetric splitting, the latter forming a stem cell and a progenitor cell. According to the differentiation ability of stem cells, they can be divided into pluripotent stem cells, pluripotent stem cells, and unipotent stem cells. The omnipotent stem cells can differentiate into any kind of cells in the body until a complex organism is formed. Pluripotent stem cells can differentiate into many types of cells, such as hematopoietic stem cells, which can differentiate into 12 kinds of blood cells. [Embryonic stem cells] Stem cells can be divided into embryonic stem cells and adult stem cells according to the order of occurrence in the development of the individual. Embryonic stem cells (ESC) refer to pluripotent or pluripotent cells isolated from embryonic inner cell masses or primordial germ cells, and can also be obtained by somatic cell nuclear transfer technology. ESC can express the transcription factor Oct-3/4 of the POU family; teratomas that can be formed after transplantation can differentiate into somatic cells representing the structure of the three germ layers under appropriate conditions in vitro. The main uses of ESC are: 1 cloned animal, which is produced by cloning of somatic cells as a nuclear donor. Although it is easy to obtain, the cloned animal exhibits serious physiological or immunodeficiency and is mostly fatal; 2 transgenic animals With ESC cells as a carrier, the speed of transgenic animal production can be greatly accelerated, and the success rate can be improved. 3 Tissue engineering, artificially induced ESC directed differentiation, and the development of specific tissues and organs for medical treatment purposes. The Wnt signaling pathway is a complex network of protein action that functions most commonly in embryonic development and cancer, but is also involved in the normal physiological processes of adult animals. [Discovery of Wnt signaling pathway] Wnt is named after Wg (wingless) and Int.wingless genes were first discovered in Drosophila and acted on embryonic development, and the INT gene of adult animals was first discovered in vertebrates, located in small The mouse mammary gland tumor virus (MMTV) integration site is nearby. The Int-1 gene shares homology with the wingless gene. Mutations in the wingless gene in Drosophila can lead to wingless malformations, whereas replication and integration of MMTV into the genome in mouse mammary tumors results in increased synthesis of one or several Wnt genes. [The mechanism of the Wnt signaling pathway] The Wnt signaling pathway includes a number of proteins that regulate the synthesis of Wnt signaling molecules, which interact with receptors on target cells, while the physiological responses of target cells are derived from the interaction of cellular and extracellular Wnt ligands. effect. Although the occurrence and intensity of the response vary with Wnt ligands, cell types and the body itself, certain components of the signaling pathway are highly homologous from nematodes to humans. The homology of proteins suggests that a variety of distinct Wnt ligands are derived from the common ancestor of various organisms. The canonical Wnt pathway describes a series of responses following the binding of the Wnt protein to the cell surface Frizzled receptor family, including activation of the Dishevelled receptor family of proteins and changes in the final nuclear β-catenin levels. Dishevelled (DSH) is a key component of the cell membrane-associated Wnt receptor complex, which is activated upon binding to Wnt and inhibits downstream protein complexes, including axin, GSK-3, and APC proteins. The axin/GSK-3/APC complex promotes the degradation of the intracellular signaling molecule β-catenin. When the "β-catenin degradation complex" is inhibited, β-catenin in the cytoplasm is stably present, and some β-catenin enters the nucleus and the TCF/LEF transcription factor family and promotes the expression of specific genes.