Submitted to: Fish Physiology and Biochemistry Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/18/2012
Publication Date: 1/31/2012
Citation: Gahr, S.A., Weber, G.M., Rexroad Iii, C.E. 2012. Identification and expression of Smads associated with TGF-beta/activin/nodal signaling pathways in the rainbow trout (Oncorhynuchus mykiss). Fish Physiology and Biochemistry Journal. DOI: 10.1007/s10695-012-9611-7.
Interpretive Summary: The Smad proteins are essential components of the biochemical processes involved in the regulation of muscle growth, reproduction, and immune responses in fish as in mammals. To gain a better understanding of how these genes function in fish, we first conducted a genetic analysis of the Smad genes in rainbow trout. Comparisons of trout Smad genes with those from other species suggests they evolved through the combination of an ancient teleost and more recent salmonid genome duplication events that resulted in multiple copies of each gene in the genome. A preliminary survey of their expression patterns included tissue distribution, embryonic expression, and modulation of expression following a short term growth hormone (GH) treatment. Based on the embryonic expression and tissue distribution, the activity of the Smads identified in the rainbow trout is similar to that observed in other species; GH treatment was shown to impact their effects on biochemical processes underlying production traits. These findings provide a basis for identifying the actions of these genes in the regulation of many critical physiological functions in fish.
Technical Abstract: The Smad proteins are essential components of the TGF-beta/activin/nodal family signaling pathway. We report the identification and characterization of transcripts representing 3 receptor Smads (Smad2a, Smad2b, Smad3), 2 common Smads (Smad4a, Smad4b) and one inhibitory Smad (Smad7). Phylogenetic analysis suggests these genes evolved through the combination of an ancient teleost and more recent salmonid genome duplication events. Tissue distribution, embryonic expression, and modulation of expression following a short term growth hormone (GH) treatment were assessed by reverse transcription PCR (RT-PCR) or qPCR. We observed the highest expression of the receptor Smads in the unfertilized egg, generally decreasing during early embryonic development and slightly increasing after about day 11 post fertilization. Smad4a and Smad7 were more variable. All six of the Smad transcripts were ubiquitously expressed in the adult rainbow trout tissues surveyed. Muscle, stomach and gill filaments showed increased expression and the kidney showed down regulation of Smads, following GH treatment. Changes in expression of various TGF-beta superfamily transcripts that may have contributed to changes in Smad expression in response to the GH treatment were also measured by qPCR and observed to be altered. Based on the embryonic expression and tissue distribution, the activity of the Smads identified in the rainbow trout is similar to that found in other species, and GH treatment was shown to impact multiple components of the TGF-beta superfamily system.