Identification of TGF-β, inhibin βA and follistatin paralogs in the rainbow trout genome

Since their initial discovery, TGF-beta superfamily members have been considered multifunctional growth and differentiation factors in many cell types. Various studies have clearly demonstrated the key roles of specific TGF-beta members in muscle growth, including myostatin and inhibin as well as genes, such as follistatin. By binding to TGF-beta members, follistatin prevents TGF-beta from binding to its receptors and thus neutralizes its activity. Here, we report the identification of the gene sequences of four TGF-beta isoforms and three paralogs of TGF-beta 1, which we called TGF-beta 1a, TGF-beta 1b and TGF-beta 1c, four sequences of inhibin beta A paralogs; and two sequences of follistatin paralogs from rainbow trout. A phylogenetic analysis clearly indicated the existence of four monophyletic clades, corresponding to TGF-beta 1, -beta 2, -beta 3 and -beta 6. Based on their sequence identity TGF-beta 1a and -beta 1c are grouped together, whereas TGF-beta 1b appears more divergent even though it is grouped within the TGF-beta 1 clade. Alignments and phylogenetic analyses showed that the protein sequences of TGF-beta, inhibin beta A and follistatin are extremely well conserved (>90%) relative to each other; however, their regulation and expression-patterns are different. TGF-beta 2 and -beta 3 showed the most abundant expression in muscle and were-the main TGF-beta members expressed in this tissue. Follistatin and inhibin beta A paralogs were expressed in all tissues examined but with different patterns. Our identification of multiple copies of TGF-beta, inhibin beta A and follistatin with different expression patterns suggests non-redundant functions for these paralogs in rainbow trout. (C) 2014 Elsevier Inc. All rights reserved.