| Although much is now known about the pharmacology of GABA{dollar}sb{lcub}rm A{rcub}{dollar} receptors, the mechanisms of transcriptional regulation of GABA{dollar}sb{lcub}rm A{rcub}{dollar} receptor subunit genes remain to be elucidated. Due to their differential distribution in the central nervous system, the family of genes encoding GABA{dollar}sb{lcub}rm A{rcub}{dollar} receptor subunits provide an excellent model for studying mechanisms leading to cell type-specific gene expression patterns in the central nervous system.; This work describes the isolation and characterization of the 5{dollar}spprime{dollar} end of the rat, mouse and human {dollar}alpha{dollar}6 subunit genes. The {dollar}alpha{dollar}6 subunit, which is expressed in cerebellar granule cells and embryonically related cells of the cochlear nucleus, displays the most restricted expression pattern of any GABA{dollar}sb{lcub}rm A{rcub}{dollar} receptor subunit gene to date, indicating a specialized function for receptors containing this subunit. Sequence comparison studies reveal that the position of the first and second introns is completely conserved. Based on our knowledge of the intron/exon structure at the 5{dollar}spprime{dollar} end of the rat {dollar}alpha{dollar}6 gene, we isolated sequences upstream of the 5{dollar}spprime{dollar} end of the published rat {dollar}alpha{dollar}6 cDNA sequence. The transcriptional initiation sites of the rat and mouse {dollar}alpha{dollar}6 genes were located using primer extension analysis and RNase protection. A promoter has been identified within the 5{dollar}spprime{dollar} flanking region of the {dollar}alpha{dollar}6 gene which is capable of conferring cell- and tissue-specific expression in primary cultures of rat cerebellum. Furthermore, a 155-bp region of the {dollar}alpha{dollar}6 promoter has been determined to be capable of sustaining cerebellar granule cell specific expression.; In addition, PCR was used to localize the {dollar}alpha{dollar}4 subunit gene of the GABA{dollar}sb{lcub}rm A{rcub}{dollar} receptor to human chromosome 4. The {dollar}alpha{dollar}4 gene is located on chromosome 4p14-q12, in a region that also contains the {dollar}alpha{dollar}2, {dollar}beta{dollar}1 and {dollar}gamma{dollar}1 genes. The presence of an {dollar}alpha{dollar}2-{dollar}alpha{dollar}4-{dollar}beta{dollar}1-{dollar}gamma{dollar}1 gene cluster on human chromosome 4 and an {dollar}alpha{dollar}1-{dollar}alpha{dollar}6-{dollar}beta{dollar}2-{dollar}gamma{dollar}2 gene cluster on chromosome 5, taken together with the fact that the {dollar}alpha{dollar}1, {dollar}alpha{dollar}2, {dollar}alpha{dollar}4 and {dollar}alpha{dollar}6 genes exhibit about 70% sequence identity, suggests that duplication of an ancestral {dollar}alpha{dollar} subunit gene occurred prior to the duplication of at least one of the original gene clusters. |
