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| Developing cells gains specificity in function as they "choose" what particular type fo cells to become. However this also includes a decrease in flexibility in ability to become other cells. |
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| Is cell differentiation something intrinsically controlled and determined or does it depend on the local signals... |
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In Nematodes, cell fate is determined by lineage. More specificially a lineage named Q develops the ability for mechanosensory stimulation to be processed.
Q cells give rise to Q1a and Q1p cells. Q1a cells make ciliated neurons while Q1p cells go on to make touch cells and interneurons. Mutations in unc-86 genes prevent Q cell from producing Q1p while mutations in mec-3 prevent Q1p cells to make touch cells.--> Genes work in cascades |
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| Cell lineages can be initiated by assymeterical cell divisions of neuroblast. In Drosophila, this is the case with the neuroblasts that were internalized through lateral inhibition. The smaller cells of the division will generate ganglions. |
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| Protein that binds to internal surface of the membrane during mitosis and is unequally distibuted among daughter cells. Contributes to differentiation of the daughter cells due to size (such as GMC) who recieve a lot of it. Mutations in Numb prevent this specification (hence in drosophila they can't feel anything--numb) |
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| In chick embryo, bagal neural crest cells produce cholinergic neurons whereas trunk cells give rise to adrenergic neurons. If you transplant quail (different species for easy tracking/identification) criss-crossing the cells and the region into a chick embryo, the new cells will produce the appropriate cell types--> phenotype must be determined by local signals |
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| Multipotent Neural Crest Progenitor |
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| Crest cells create numerous different cell types and undergo the longest migration of any of the cells in the developing nervous system |
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| Cell Fate in Cortex, Retina, Spinal Cord |
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Cortex- 6 layers, each layer has specific types. Earlier in development, the postmitotic neurons migrate to the surface nearest to the VZ (VI). Later, cells are added to more superficial layers. The older cells (migrate further) can't migrate closer but the newer cells (migrate closer) can be induced to migrate further by transplantation.
Retina-Cells are generated in a specific sequential order according to timing. Ganglion>Horizaontal>Amacrine>Cones>Bipolar>Rod>Muller
Spinal Cord- cell fate determined by location on the spinal cord (e.g. Shh generated by the notochord induces cells on the neural tube closest to it to ventralize (motor, floorplate)... Medium signal become interneuron and low Shh becomes sensory/dorsal stuff. |
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