Rainbow trout slow myoblast cell culture as a model to study slow skeletal muscle, and the characterization of and families as a case study.

Muscle fibres are classified as fast, intermediate and slow. myoblast cell culture model from fast muscle is a very useful tool to study muscle growth and development; however, similar models for slow muscle do not exist. Owing to the compartmentalization of fish muscle fibres, we have developed a slow myoblast cell culture for rainbow trout (). Slow and fast muscle-derived myoblasts have similar morphology, but with differential expression of slow muscle markers such as , and We also characterized the and microRNA families in trout slow and fast myoblasts as a case study during myogenesis and in response to electrostimulation. Three (, and ) and four (, , and ) paralogues were identified for rainbow trout and named base on their phylogenetic relationship to zebrafish and Atlantic salmon orthologues. and had 0.6 and 0.5-fold higher expression in slow myoblasts compared with fast myoblasts, whereas duplicates had similar levels in both phenotypes and little variation during development. Slow myoblasts also showed increased expression for paralogues in response to chronic electrostimulation (7-fold increase for and 2.5-fold increase for ). The higher expression of paralogues in slow myoblasts suggests a role in phenotype determination, while the lack of significant differences of copies during culture development might indicate a different role in fish compared with mammals. We have also found signs of sub-functionalization of paralogues after electrostimulation, with copies more responsive to electrical signals.