Distribution of the voltage-dependent calcium channel alpha1G subunit mRNA and protein throughout the mature rat brain.

The molecular identity of a gene which encodes the pore-forming subunit (alpha1G) of a member of the family of low-voltage-activated, T-type, voltage-dependent calcium channels has been described recently. Although northern mRNA analyses have shown alpha1G to be expressed predominantly in the brain, the detailed cellular distribution of this protein in the central nervous system (CNS) has not yet been reported. The current study describes the preparation of a subunit specific alpha1G riboprobe and antiserum which have been used in parallel in situ mRNA hybridization and immunohistochemical studies to localize alpha1G in the mature rat brain. Both alpha1G mRNA and protein were widely distributed throughout the brain, but variations were observed in the relative level of expression in discrete nuclei. Immunoreactivity for alpha1G was typically localized in both the soma and dendrites of many neurons. Whilst alpha1G protein and mRNA expression were often observed in cells known to exhibit T-type current activity, some was also noted in regions, e.g. cerebellar granule cells, in which T-type activity has not been described. These observations may reflect differences between the subcellular distribution of channels that can be identified by immunohistochemical methods compared with electrophysiological techniques.

Homology between the cDNAs encoding phosphoprotein p19 and SCG10 reveals a novel mammalian gene family preferentially expressed in developing brain.

We have isolated and sequenced a rat testis cDNA encoding p19, a 19-kD cytosolic phosphoprotein that is abundant in immature brain, testis, and neuroendocrine tumor cells. The cDNA was identified using bovine brain p19 peptide sequences, which indicate that the gene encoding p19 has been highly conserved during mammalian evolution. Using Northern blot analysis on rat tissues, p19 mRNA was readily detected in brain and testis and showed a 15-fold greater abundance in newborn than in adult brain. Low levels of p19 mRNA were observed in spleen, kidney, and heart, but not in liver. Thus, the expression of the gene encoding p19 shows a strong tissue preference and is developmentally regulated. The predicted amino acid sequence of p19 is highly homologous to that of SCG10, another protein expressed in the developing rat nervous system, suggesting that the two proteins serve similar functions. Based on a comparison of the two cDNAs, we conclude that p19 and SCG10 are encoded by distinct but related genes constituting a novel gene family.