Molecular cloning and localization of the human GAX gene to 7p21

The GAX homeobox gene is expressed in the cardiovascular tissues of the adult rat, including heart, lung, kidney, and blood vessels. In the vasculature it is specifically expressed in quiescent smooth muscle cells, but its expression is rapidly down-regulated when these cells are stimulated to proliferate with mitogens. Since vascular smooth muscle cell proliferation is important in the pathology of blood vessel disorders, the human GAX gene was isolated and characterized. The human GAX cDNA was obtained by an anchored-PCR approach using cDNA templates from cardiovascular tissues and amplification primers designed from sequence information of the rat GAX cDNA and the homeodomain-containing exon of the human GAX gene. The human and rat GAX gene coding sequences are 98% conserved at the amino acid level and 83% conserved at the nucleotide level. Similar to rat, the human homolog contains a CAX trinucleotide repeat N-terminal to the homeodomain that encodes for a stretch of 17 consecutive histidine or glutamine residues. The human GAX locus was mapped by fluorescence in situ hybridization to the short arm of chromosome 7 at band p21. The human cDNA sequence will be useful for analyses of GAX gene expression in cardiovascular diseases.