Cloning of MafG homologue from the rat brain by differential display and its expression after hypercapnic stimulation

The ventral medullary surface (VMS) is a site of the medullary chemorecepto r neurons which sense excess protons (H+) derived from hypercapnia and faci litate respiration. We hypothesized that expression of genes involved in H-sensitivity is higher in the VMS than in other central nervous system area s. By using the differential display technique, we differentiated the mRNAs of VMS neurons from those of cerebral cortical neurons. Seventeen clones o f interest were isolated, and sequence analysis revealed that one of these clones had an encoding nuclear transcription factor, MafG. MafG is a member of Maf protein family, and the founding member of the family (v-Maf) was o riginally discovered as the transduced transforming component of avian musc uloaponeuroticfibrosarcoma virus, AS42. The rat MafG was composed of 162 am ino acid residues and was conserved among the primary structures of various species. Expression of rat mafG mRNA is high in the VMS, heart and skeleta l muscle while the cerebral cortex, cerebellum, liver, stomach and intestin e show moderate expression. To determine whether the expression of mafG mRN A is induced by hypercapnic stimulation, 7% CO2 in air was inhaled to rats for 5 min. We found that the hypercapnic stimulation induced the gene expre ssion of mafG. These results suggest that MafG may be involved in H+-sensit ivity and respiratory regulation in the VMS.