The central nervous system consists of two types of cells: neuronal and glial cells. This research focused on glial cells and the Notch pathway which is a gene regulatory pathway involved in multiple differentiation processes. The Notch cascade consists of Notch and Notch ligands, as well as intracellular proteins transmitting the Notch signal to the cell’s nucleus. The Notch receptor family was found to be involved in the specification of cell fates during development in drosophilla. Interestingly, the Notch signaling pathway begins to inhibit new cell growth when adolescence is reached, and keeps neural networks stable in adulthood. The hypothesis that this research aims to test is that the Notch signaling pathway regulates the glial development in the embryonic chick brain. To test this hypothesis we have used a synthetic drug (3, 5- Difluorophenylacetyl)-Ala-Phg-OBu (DAPT), which inhibits a specific step in the Notch pathway, and then measured the effects on glial development in vitro. The optic tectum (OT, i.e. a specific brain region) of 7 day old white leghorn chick embryos was used as the experimental system. The tissue was dissociated into single cells and then placed in reaggregation culture for 11 days with and without the addition of DAPT. After the incubation period, reaggregate cultures were harvested and processed for biochemical analyses of cell marker expression and for immunohistochemical analyses of histological sections. Markers of glial differentiation such as GFAP and GS (markers of astrocytes) showed much lower levels of expression after DAPT treatment. In contrast, several markers of neuronal differentiation showed relative increases in expression. The results showed that the inhibition of Notch signaling pathway reduced the maturation of certain types of glial cells (astroglia) and surprisingly may have enhanced the relative development of others (oligodendroglia). There was an enhanced relative expression or accumulation of certain neuronal markers after exposure to DAPT.

[Proc Amer Assoc Cancer Res, Volume 47, 2006]