NEUROGENESIS AND GLIOGENESIS IN THE DEVELOPING BRAIN

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The NF-1 and AP-1 transcription factors have adjacent binding sites in the regulatory region of a number of genes. Because of the possible involvement of NF-1 with the expression of genes expressed in the CNS/PNS, we have screened cDNA libraries prepared from human neonatal and fetal brain tissue for the possible presence of a brain specific NF-1 factor with an oligonucleotide probe homologous with the DNA binding domain of the NF-1. Two clones from the neonatal brain library and one clone from the fetal brain library were sequenced. The 3 sequenced cDNA clones were homologous with each other, except for a few bases at the 5' end of the two longest clones and a 150-bp insertion in the 3'-region of the shortest clone. The DNA binding region located at the 5'-end of the clones was highly conserved between the brain clones and that reported for the HeLA NF-1 clone. On the other hand, the 3'-region of the c-DNA clones isolated from the brain libraries were highly homologous but differed from that reported from HeLA cells. The 3'-region of the NF-1 molecules were reported to contain the transcriptional activational domain of the molecular. One of the brain cDNA clones was cloned into a T7 RNA polymerase expression vector, and a specific size protein was overproduced on induction of expression with IPTG. An extract prepared from cells overproducing the specific protein was demonstrated to contain specific binding activity. In order to determine if other classes of NF- 1 could be detected in primary fetal brain cells, RT-PCR analysis was performed with poly A-selected RNA from primary fetal cells and HeLa cells. With the use of class-specific primers the expression of at least four classes of the NF-1 protein family could be detected in both the brain and the HeLA cell lines. In the fetal brain cultures, however, one clone, NF-1/AT1 was highly expressed compared with the other 3 classes. Astrocyte cultures were also analyzed for expression of arachidonic acid metabolites in response to cytokine stimulation. In the presence of IL-1 beta, human astrocytes produce prostaglandin E2 and prostaglandin F2 alpha. Other intermediate compounds in the cyclooxygenase pathway are not made unlike similar cultures of rodent astrocytes. Both of these studies highlight the fact that human astrocytes have phenotypic and genotypic differences compared with rodent models of neuro and gliogenesis.