6- epigenetic
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Adult stem cells are:
multipotent
Hematopoiesis:
an example of stem cell differentiation
When a cell in a multicellular organism becomes committed to differentiate into a specific cell type, the:
terminal fate is normally maintained through all subsequent generations
a signal (external or internal) triggers changes in the:
expression of genes that direct the cell toward a particular differentiation pathway
changes in gene expression must be remembered when the cell divides:
the cell must retain a memory of these original instructions
non-genetic cellular memory is the basis of:
epigenetics
Epigenetics is the study of:
changes and variations in phenotypes that are potentially heritable, but are not caused by permanent changes in DNA base sequences
Facultative heterochromatin are the regions of the chromosomes that:
contain genes but can become heterochromatic depending on the cell type. As cells differentiate, they convert more of their DNA into heterochromatin
Embryonic and adult stem cells have less:
facultative heterochromatin than terminally differentiated cells.
Groups of transcription regulatory proteins work together to:
control the expression of single genes
transcription regulators bind to specific:
regulatory DNA sequence elements near genes, and together with general transcription factors and RNA polymerase form the transcription initiation complex
some of these regulators are activators while others are repressors, and their effects:
are added up to determine the final level of expression of the gene
if any one of these transcription regulators is subtracted from the transcription initiation complex, transcription levels may be:
significantly altered or it may not occur at all, because the complex would be incomplete
The expression of a single transcription regulator can be decisive in:
switching on or off a gene or group of genes
the same protein could also be one that completes the transcription initiation complexes regulating several genes, thus:
switching ON (or OFF) several genes at once
Because the effect of transcription regulators is combinatorial:
the addition of a single, missing protein can complete a complex that switches a gene ON
example: the glucocorticoid receptor is a transcription regulator that can activate the transcription of:
several genes involved in the glucocorticoid response when the hormone binds to it
All the muscle-specific genes required for the specification of skeletal muscle cells can be:
switched on by the action of a single transcription regulator: MyoD.
MyoD commits cells to become:
myoblasts (muscle cell precursors)
these cells then proliferate and eventually fuse to form the:
multinucleated myotubes that become muscle fibers
muscle fibers express a number of muscle specific products, which give:
the muscle cells their specific properties
If MyoD is artificially expressed in fibroblasts, a cell type that belongs to the same broad class of embryonic cells as muscle cells but is:
involved in wound healing, the cells start to behave as myoblasts and fuse to form muscle-like cells
It appears that myoblasts already contain the other transcriptional regulators required for the combinatorial induction of the muscle fate, and the addition of MyoD completes:
a unique combination. Other cell types that are not related to muscle cells do not respond the same way
*fibroblasts are: *and stained to detect
*transdifferentiated by the experimental expression of MyoD *muscle-specific proteins.