Differential expression of two nonallelic MyoD genes in developing and adult myotomal musculature of the trout ( Oncorhynchus mykiss )

Abstract

Previously we identified two nonallelic MyoD encoding genes in the rainbow trout. These two MyoD genes (TMyoD and TMyoD2) were duplicated during the tetraploidization of the salmonid genome. In this study we show that TMyoD and TMyoD2 exhibit a distinct spatiotemporal pattern of expression that defines discrete cell populations in the developing somite. TMyoD expression is first detected in the mid-gastrula on either side of the elongating embryonic shield. During the anterior-to-posterior wave of somite formation the TMyoD transcript is initially present in adaxial cells of both the presomitic mesoderm and the forming somites. A lateral extension of TMyoD expression occurs only when the myotomes acquire their characteristic chevron shape pointing rostrally. By contrast, the initial expression of TMyoD2 occurs in somites that have already formed and is limited to the posterior compartment of somites. Further, in postlarval trout we observed a differential expression of TMyoD and TMyoD2 genes in muscle fibers with differing phenotype. Collectively, these data provide evidence that the two trout MyoD encoding genes have evolved to become functionally different. A comparison of the expression patterns of the two trout MyoD genes with that of myogenin allowed us to position them in the regulatory pathway leading to muscle differentiation.

Analysis of muscle fibre input dynamics using amyog: GFP transgenic trout model

“…Additionally, fluorescence was found to progress caudally as somites matured in a rostral-to-caudal wave. Thus, spatial myog:GFP expression is consistent with endogenous myogenin expression (Delalande and Rescan, 1999), suggesting that the promoter fragment we used contains the regulatory sequence necessary to recapitulate the endogenous expression pattern. However, embryonic GFP fluorescence was only detected at 11 dpf, whereas evidence of myogenin transcripts was found earlier, at approximately 8 dpf (Delalande and Rescan, 1999).…”

“…Thus, spatial myog:GFP expression is consistent with endogenous myogenin expression (Delalande and Rescan, 1999), suggesting that the promoter fragment we used contains the regulatory sequence necessary to recapitulate the endogenous expression pattern. However, embryonic GFP fluorescence was only detected at 11 dpf, whereas evidence of myogenin transcripts was found earlier, at approximately 8 dpf (Delalande and Rescan, 1999). This discrepancy probably relates to the fact that detection of GFP fluorescence in our transgenic trout involves not only the production of the myogenin-driven GFP-encoding transcript but also its translation into proteins and their accumulation to generate enough fluorescence to be imaged.…”

“…Thus, gilthead sea bream retain two paralogues of myod (myod1 and myod2) (Tan and Du, 2002). By contrast, the salmonid lineage lost myod2 but, as a result of additional duplications, gained three myod1 paralogues (Macqueen and Johnston, 2006) that have distinct developmental expression patterns (Delalande and Rescan, 1999;Macqueen and Johnston, 2006). Only a single myogenin gene has been identified to date in teleosts (Rescan et al, 1995;Weinberg et al, 1996;Macqueen et al, 2007;Codina et al, 2008).…”

“…Only a single myogenin gene has been identified to date in teleosts (Rescan et al, 1995;Weinberg et al, 1996;Macqueen et al, 2007;Codina et al, 2008). Myogenin expression in teleosts, as in mammals, starts just before muscle differentiation both in vivo and in vitro (Rescan et al, 1995;Weinberg et al, 1996;Delalande and Rescan, 1999;Codina et al, 2008;García de la Serrana et al, 2014).…”

Expression of Growth-Related Factors in Skeletal Muscle of Pirarucu(Arapaima Gigas) during Growth

“…In this work, all groups showed intensive growth rates, as many of their fibers were newly formed. These findings suggest an atypical behavior for pirarucu muscle growth compared with other fish species [71][72][73][74], since all groups had similar characteristics of fish at initial stages, i.e., fast muscle growth [3,4,70]. As pirarucu achieves large size in the adult stage, the creation of many fibers during the first developmental stages is the best strategy to improve muscle growth.…”