Structure and methylation of the human calcitonin/alpha-CGRP gene

We report a detailed analysis of the human calcitonin/alpha-CGRP gene locus. About 39kb of DNA containing the gene has been mapped and a common Pvu II RFLP identified downstream of the gene. DNA sequence analysis revealed an extensive CpG island containing several rare restriction enzyme sites at the 5' end of the gene. The structure of this island is unusual in that it contains two distinct CpG-rich regions, one located around exon 1 and the other about 1.5kb further upstream. Msp I sites within both CpG-rich regions were found to be unmethylated, regardless of whether the calcitonin/alpha-CGRP gene was being expressed. However, a correlation was found between demethylation of Msp I sites in intron 2, downstream of the CpG island, and calcitonin/alpha-CGRP gene expression. DNA sequence analysis also revealed the presence of several binding sites for constitutive and regulatory transcription factors in the promoter of the gene. These results suggest that both unmethylated CpG islands and specific demethylation of internal sequences may play a role in the activation of calcitonin/alpha-CGRP gene transcription.