The two mature transcripts of the chick calcitonin gene are expressed within the central nervous system during embryogenesis.

Calcitonin mRNA and calcitonin gene-related peptide (CGRP) mRNA both are generated from the calcitonin gene because of tissue-specific alternative splicing of the primary transcript. It is currently established that, of the two mature transcripts, calcitonin mRNA is far the predominant transcript produced in thyroid C-cells whereas only CGRP mRNA is produced in the nervous system. However, here we provide evidence that the two splicing forms of the chick calcitonin primary transcript are found within the developing central nervous system, although displaying specific patterns of expression. While CGRP mRNA is first expressed in motor neurons at rather advanced stages of embryogenesis, calcitonin mRNA is expressed in the floor plate and dorsal rhombencephalon from earliest stages.