CELL LINEAGES
What Role do Cell Lineages Play in Neural Differentiation?
Within the early neuroepithelium are multipotential stem cells which
form a majority of the adult neural cells. The cells go through a variety
of mitotic divisions and differentiations, in which their potential
is restricted. Multipotential cells become bipotential cells which can
only differentiate into glial or neural cells. The neuronal lineage
becomes the future neurons after a series of morphological changes.
Glial cells have a variety of functions in the nervous system. This
lineage contributes a multitude of cells which are crucial to the proper
development and function of surrounding neural cells. Radial glial cells
help guide the migrating young neural cell to it’s proper location.
Oligodendrocytes migrate throughout the nervous system and create the
myelin sheaths which greatly facilitate the
electric signals running through the nerve cells. (1)
What Types of Factors Help to Control the Formation of These Lineages?
One group of researchers were able to culture ES cells in vitro and coax the cells to differentiate and become functional postmitotic neurons. Neuroepithelial precursor cells from ES cells proliferated in the presence of basic fibroblast growth factor (bFGF) without differentiating. These cells differentiated into neurons and glia cells bFGF when they were taken out of the media. The cells continued to differentiate into a wide variety of neural cell types when they were placed in a media containing serum. En1, and Hoxa-7. (25)
This photo illustrates how glial cells myelenate nerve fibers. (1)
Another group of researchers found that the oligodendrocyte-type-2 astrocyte (O-2A) lineage gives rise to oligodendrocytes and type 2 astroctyes (two different glial cell populations). Oligodendrocytes fully differentiate from O-2A cells when in direct contact to type 1-astrocyte cells. They also differentiate in response to platelet-derived growth factor (PDGF) which could be a product of nerve cells in general since nerve cells can also induce O-2A cells to differentiate. bFGF can also cause O-2A to divide and develop. However, when the O-2A cells are exposed to both PDGF and bFGF, the cells failed to differentiate at all. The concerted effect of both factors prevent differentiation, but allow division and proliferation. More specifically, the team found that the proliferation of O-2A progenitor cells is best in cocktail of PDGF, bFGF, neurotrophin-3, and forskolin, in absence of thyroid hormones and ciliary neurotrophic factors. This combined treatement of factors can be used to increase the population of a group of stem cells. (30)