Developmental regulation and neuronal expression of the mRNA of rat n-chimaerin, a p21rac GAP:cDNA sequence

Human n-chimaerin is a GTPase-activating protein (GAP) for p21rac and a phorbol ester receptor. We have isolated rat n-chimaerin cDNA and investigated the cellular and developmental pattern of mRNA expression in the brain. There is extensive sequence conservation with human n-chimaerin in the coding region and the first 400 nucleotides of the 3'-untranslated region (UTR) (90% and 83% identity respectively). The rat cDNA encodes an additional 35 N-terminal amino acids compared with the reported human cDNA, which has a 5'-UTR sequence inversion and a 41-nucleotide deletion including the putative initiator methionine. The rat cDNA encodes a 334-amino acid protein (38200 M(r), pI 8.04) with 97% amino acid sequence identity with the human protein, after correction of the human 5'-DNA sequence. n-Chimaerin mRNA was detectable in embryonic rat brain at day 15 and increased in amount postnatally from birth to 20 days, coincident with cellular differentiation and synaptogenesis. n-Chimaerin mRNA is restricted to neurons, with highest concentrations in hippocampal pyramidal cells, granule cells of the dentate gyrus and cortical neurons. In the cerebellum the mRNA was detected only in Purkinje neurons. The pattern and specificity of mRNA expression suggests an important role for n-chimaerin in neuronal signal-transduction mechanisms.