|Garikipati, Dilip - WASHINGTON ST UNIVERSITY|
|Roalson, Eric - WASHINGTON ST UNIVERSITY|
|Rodgers, Buel - WASHINGTON ST UNIVERSITY|
Submitted to: Endocrinology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 26, 2007
Publication Date: February 8, 2007
Citation: Garikipati, D.K., Gahr, S.A., Roalson, E.H., Rodgers, B.D. 2007. Characterization of rainbow trout myostatin-2 genes (rtMSTN-2a & -2b): genomic organization, differential expression and pseudogenization. Endocrinology 148:2106-2115. Interpretive Summary: Myostatin (MSTN) is a member of the TGF-beta superfamily and a potent negative regulator of skeletal muscle growth in mammals. Myostatin null phenotypes in rodents and cattle are characterized by extreme gains in muscle mass commonly referred to as “double muscling." Unlike mammals, in fish multiple myostatin genes have been identified and expression has been isolated in a number of different tissues. In this paper, we report the discovery of MSTN-2a and -2b genes in the rainbow trout, the genomic organization of both genes, including their respective promoter regions, and the quantitative assessment of rtMSTN-2a gene expression during embryonic development and in various adult tissues. These results are the first to confirm the existence of four myostatin genes in any salmonid species and reveal a strong conservation of genomic organization among all vertebrate homologs. In addition, we identified rtMSTN-2b as a pseudogene as well as unspliced transcripts of both rtMTSN-2a and -2b, which has never been described in any vertebrate.
Technical Abstract: Myostatin is an extremely potent negative regulator of vertebrate skeletal muscle development. A phylogenetic analysis suggests that salmonids should possess four distinct genes, although only MSTN-1 orthologs have been characterized. Described herein are the rainbow trout (rt) MSTN-2a and -2b genes, subsequence analysis of their promoters and their quantitative expression profiles. Both genes are similarly organized, contain several putative myogenic response elements and are legitimate MSTN-2 orthologs based on Bayesian analyses. However, rtMSTN-2b contains two in-frame stop codons within the first exon and unspliced variants of both transcripts were expressed in a tissue specific manner. Complete splicing of rtMSTN-2a only occurred in brain, where expression is highest, while rtMSTN-2b transcripts were mostly present in unspliced forms. The presence of stop codons in the rtMSTN-2b open reading frame and the expression of mostly unspliced transcripts indicates that this particular homolog is a pseudogene. These results confirm our previous phylogenetic analysis and suggest that all salmonids likely possess four distinct myostatin genes. The tissue-specific expression and differential processing of both rtMSTN-2 transcripts as well the pseudogenization of rtMSTN-2b may reflect compensatory and adaptive responses to tetraploidization and may help limit rtMSTN-2a's influences primarily to neural tissue.