Molecular analysis and chromosomal assignment of the canine CALC-I/alpha-CGRP gene

We have isolated a recombinant phage harboring the canine CALC-I/alpha-CGRP gene. The gene spans a region of approx. 5.3 kb and consists of six exons with sizes ranging from 95 bp (exon 2) and 494 bp (exon 4). By alternative splicing, two transcripts with ORFs of 390 and 384 nt are generated. These encode either the 32-amino acid-long hormone calcitonin (CALC or the neurot ransmitter calcitonin gene-related peptide (alpha-CGRP) with a length of 37 amino acids after proteolytic processing of precursor molecules. The canin e calcitonin precursor consists of 130 amino acids with a molecular mass of 14.05 kDa and a statistical pi of 8.0, whereas the deduced alpha-CGRP prec ursor harbors 128 amino acids with a molecular mass of 13.87 kDa and a stat istical pi of 8.6. Both polypeptides have a common N-terminal region of 76 amino acids that is encoded by exons 2 and 3 and separated by different eig ht (CALC) or six (alpha-CGRP) amino acid spacers from the biologically acti ve polypeptide. The CALC-I/alpha-CGRP gene is a member of the calcitonin ge ne family and was assigned to chromosome CFA 16q35.1. A comparative analysi s of different dog breeds revealed a breed-specific allelic d(CAGGAG)-hexan ucleotide expansion in exon 3. This expansion results in an elongation of t he common N-terminal region by two amino acids (glutamine-glutamic acid) an d alters the molecular mass to 14.31 kDa (pI 7.9) and 14.13 kDa (pI 8.5) of the calcitonin and alpha-CGRP precursor, respectively.