Expression of the genes for alpha-type and beta-type calcitonin gene-related peptide during rat embryogenesis

Throughout rat embryogenesis we analysed the expression patterns of the thr ee mature transcripts generated from the two calcitonin gene-related peptid e genes: calcitonin, alpha-calcitonin gene-related peptide, and beta-calcit onin gene-related peptide messenger RNAs. In addition, we examined in paral lel the distribution of calcitonin gene-related peptide and calcitonin immu noreactivity. Of the three transcripts, beta-calcitonin gene-related peptid e messenger RNA was first detected in sensory ganglia on embryonic day 14, and by embryonic day 15 was seen to a lesser degree in motor neurons and au tonomic ganglia. Starting at embryonic day 16, however, the highest levels of beta-calcitonin gene-related peptide messenger RNA were found in motor n eurons rather than sensory ganglia. alpha-calcitonin gene-related peptide m essenger RNA was first detected on embryonic day 16 in both sensory ganglia and motor neurons, but at lower levels than beta-calcitonin gene-related p eptide, particularly in the motor neurons of the spinal cord. By embryonic day 20, transcripts for alpha- and beta-calcitonin gene-related peptide wer e expressed in distinct brain regions. High levels of alpha-calcitonin gene -related peptide messenger RNA were detected in hypoglossal, facial, and pa rabrachial nuclei, and moderate levels in the trigeminal motor and ambiguus nuclei. By contrast, beta-calcitonin gene-related peptide messenger RNA wa s detected at low levels in hypoglossal, ambiguus, facial, and parabrachial nuclei, and at high levels in the trigeminal nucleus. In the oculomotor-tr ochlear nucleus, beta-calcitonin gene-related peptide messenger RNA was the sole isotype expressed. Low levels of messenger RNA for both calcitonin ge ne-related peptide transcripts were appreciated in the inferior olive. Outs ide the nervous system, alpha-calcitonin gene-related peptide messenger RNA was weakly expressed in the thyroid gland and beta-calcitonin gene-related peptide messenger RNA in the thymus. Throughout embryogenesis, calcitonin gene-related peptide immunoreactivity usually followed the expression of ei ther alpha- or beta-calcitonin gene-related peptide messenger RNA. Calciton in messenger RNA and protein were detected only in the thyroid gland from e mbryonic day 18 onward, This work shows that of the three mature transcripts produced by the two ca lcitonin gene-related peptide genes, beta-calcitonin gene-related peptide m essenger RNA is the predominant transcript produced early in rat embryogene sis. However, by perinatal stages alpha-calcitonin gene-related peptide sho ws the highest expression in the brain and spinal cord. In autonomic gangli a, beta-calcitonin gene-related peptide is either the sole or the predomina nt transcript. Unlike the chick embryo in which calcitonin messenger RNA is expressed early in the CNS, in rat it was only expressed outside the nervo us system in the thyroid gland during the last days of embryogenesis. (C) 1 999 IBRO. Published by Elsevier Science Ltd.