Stem cells and regeneration

stem cells are capable of self renewal because when they divide…

at least one daughter cell s a stem cell so they are always replacing themselves

totipotent

can become any cell in an organism; only present during the first few cell division in embryogenesis

pluripotent cell

can become nearly any cell in an organism

multipotent cells

can become any cell within a particular tissue or organ

unipotent cell

can only become one type of cell (stem cells are not unipotent)

progenitor

will eventually become terminally differentiated

to achieve self-renewal, stem cells often go through…

asymmetric divisions

mechanistically, why do stem cells undergo asymmetric division?

prior to mitosis, certain “stem” factors are polarized into one side of the cell; following cytokinesis, the daughter cell with no stem factors goes down the path to differentiation

or

dictated by the orientatino of the mitotic spindle —> daughters born outside the niche (or forced out early on)

stem cell niche

provides cues that keep stem cells from differentiation (via physical contacts or biochemical signals)

what happens to stem cells that leave the niche?

they go on to differentiate

importance of stem cells in the intestinal epithelium

stem cells supply new cells for this tissue that is constantly being damaged

where is the stem cell niche maintained in the intestinal epithelium

crypts (some daughter cells exit this stem cell niche after division and migrate upward, becoming different differentiated cell types) —> cell dies die off at the tope of the villus

lineage tracing

using genetics to follow the fate of cells derived from an original multipotent stem cell

“potency” of hematopoietic stem cells

multipotent because they can generate all types of blood cells

do tumors have stem cells

tumors may contain cancer stem cells

neoblasts

stem cells in flat worms that can give rise to any cell in the organismn —> allow planaria to regrow practically any part of their body

axolotl limb is cut off…what structure forms as the limb regenerates

blastema

what does a blastema contain

activated stem cells and progenitor cells; proceeds much like original development does

quiescent cells

cells that have temporarily exited the cell cycle

satellite cells

cells in muscle are quiescent stem cels because muscle cells do not neet to be constantly replenished; become activated and proliferate in response to muscle damage, helpint to rebuild the tissue

ES

embryonic cells; derived from blastocyst embryos

properties of ES cells

1. can go through many rounds of cell division via upregulation of telomerase to maintain telomere length

2. much more euchromatin —> allows for flexibility of gene expression

3. express ES-critical genes taht maintain pluripotency

iPS

induced pluripotent stem cells; non-stem cells modified to behave like pluripotent stem cells

what transcription factors are upregulated in pluripotent cells

1. Oct4

2. Sox2

3. Klf4

4. Myc

(AKA OSKM)

characteristics of stable iPS cells

stable expression of OSKM factors on their own as well as cell-cycle promotion factors and telomerase

transdifferentation

fibroblasts are forced to express genes of a certain target tissue, promoting conversion into that cell type; these cells may retain some characteristics of their starting point and may not be suitable for all applications