Stem Cells and Differentiation PDF

Video 41: Stem Cells and Differentiation, Part I Slide 3: Stem cell definition. Characteristics of stem cells: Can (potentially) continuously divide (self-renewal) Can differentiate into a variety of cells/tissues They are unspecialized (“blank slate”) Can divide/self-renew...

Video 41: Stem Cells and Differentiation, Part I Slide 3: Stem cell definition. Characteristics of stem cells: Can (potentially) continuously divide (self-renewal) Can differentiate into a variety of cells/tissues They are unspecialized (“blank slate”) Can divide/self-renew over long periods Can differentiate into more specialized cell types Adult stem cells are typically quiescent until needed, but some continuously proliferate, self-renew, differentiate, etc. (e.g., Lg5+ CBC cells in the intestine) Cellular differentiation is the process when cells change from one cell type to another, typically to a more specialized cell type. It is usually controlled by cell signaling pathways. In some contexts, dedifferentiation takes place; this is the process of change to a less specialized, more “stem-like” cell. Slide 4: Stem cell division and differentiation. On the schematic: A is a stem cell, B is a progenitor cell (a cell that has initiated differentiation), C is a differentiated cell. 1 is a symmetric stem cell division when a stem cell divides to form two new stem cells. 2 is an asymmetric stem cell division when the division results in a stem cell for maintenance and a cell that can differentiate. 3 is a progenitor division, which expands the progenitor cell population. 4 designates a terminal differentiation. Slide 5: Stem cell types Totipotent - each cell can form a new individual; for example, early human embryo (1-3 days) cells. Pluripotent - these cells can form any of over 200 cell types; example: embryonic stem cells [some human blastocyst (5-14 days) cells] Multipotent – these cells are somewhat differentiated, but can still form several tissues; examples: cells from fetal tissue, cord blood stem cells, and adult stem cells Unipotent: can only form only one lineage. Should these cells be classified as stem cells given their limited differentiation abilities? Examples are adult skin stem cells. We also differentiate professional vs. facultative stem cells. Professional designates permanent stem cells. The classic example is the Lg5+ CBC cells in the intestine. Facultative stem cells are the daughter cells that can dedifferentiate upon injury and become stem cells. A classic example is the dedifferentiation in the intestine. Slide 6: Classes of stem cells. Embryonic stem cells. For example, from an early embryo. These have a “blank slate” and can form many types of cells/tissues, typically these are pluripotent. Embryonic germ cells. These cells are derived from those parts of the (e.g., human) embryo/fetus that would eventually produce gametes (eggs or sperm). Adult stem cells. These are (relatively) undifferentiated cells that can be found among the more specialized differentiated cells in a tissue/organ (after birth). Adult stem cells typically exhibit a more restricted ability to produce various types of cells/tissues (multipotent, unipotent), as well as a somewhat more restricted ability to self-renew. Examples are skin, fat, bone marrow, intestine, brain, etc. Cord Blood Stem Cells (typically multipotent) Induced Pluripotent Stem Cells (artificial). These are adult cells made pluripotent, and functionally equivalent to embryonic stem cells.