Identification of proteins that are developmentally regulated during early cerebral corticogenesis in the rat

Between embryonic day 14 (E14) and embryonic day 21 (E21), the rat neopallium develops from a relatively homogeneous band of mitotic precursor cells into a complex laminated structure containing diverse classes of neurons. In order to identify some of the molecular components underlying this process, 2-dimensional PAGE was used to compare proteins expressed before cortical neurons are born (E14) with those expressed during neurogenesis and neuronal migration (E17 and E21). This approach has permitted the identification of 15 proteins that show greater than 3-fold changes in their rate of accumulation between E14 and E21. Six proteins show consistent up-regulation, ranging from 3.2- to 10.7-fold. Five proteins show consistent down-regulation ranging from 9- to 22-fold. Four proteins that appear at E21 are not detectable on fluorograms of E14 cortex, even after long exposures, and thus are up-regulated more than 200-fold from E14 to E21 and may be considered to appear de novo. The molecular weights and isoelectric points of most of these 15 suggest that they are previously unreported, developmentally regulated proteins. Comparisons of gels of cortex to gels of lung and heart suggest that several of these proteins are enriched in brain relative to non-neural tissues. This analysis also indicates that, despite the large morphogenic changes observed during this developmental period, few proteins (less than 3%) among the total spectrum analyzed show large changes in their rates of synthesis.