Genomic organization and neonatal expression of the bovine myostatin gene.

Myostatin belongs to the Transforming Growth Factor-beta (TGF-beta) superfamily and is expressed in developing and mature skeletal muscle. Biologically, the role of myostatin seems to be extremely well conserved during evolution since inactivating mutations in myostatin gene cause similar phenotype of heavy muscling in both mice and cattle. In this report we have analysed the genomic structure and neonatal expression of the bovine myostatin gene. The molecular analysis shows that the bovine myostatin gene consists of three exons and two introns. The sizes of the first and second exons are 506 and 374 base pairs (bp) respectively. The size of the third exon was found to be variable in length (1701 or 1812 or 1887 nucleotides), whereas the size of the two introns is 1840 and 2033 bps. In the first exon of bovine myostatin, a single transcription initiation site is found at 133 bps from the translation start codon ATG. Sequencing the 3' untranslated region indicated that there are multiple polyadenylation signals at 1301, 1401 and 1477 bp downstream from the translation stop codon (TGA). Furthermore, 3' RACE analysis confirmed that all three polyadenylation sites are used in vivo. Using quantitative RT-PCR we have analysed neonatal expression of myostatin gene. In both the M. biceps femoris and M. semitendinosus, the highest level of myostatin expression was observed on day 1 postnatally, then gradually reduced on days 8 and 14 postnatally. In contrast, in the M. gastrocnemius, myostatin expression was highest on day 14 and lowest on day 8. These results indicate that myostatin gene structure and function is well conserved during evolution and that neonatal expression of myostatin in a number of predominantly fast twitch muscles is differentially regulated.