Abstract
Activin signaling is essential for proper embryonic, skeletal muscle, and reproductive development. Duplication of the pathway in teleost fish has enabled diversification of gene function across the pathway but how gene duplication influences the function of activin signaling in non-mammalian species is poorly understood. Full characterization of activin receptor signaling pathway expression was performed across embryonic development and during early skeletal muscle growth in rainbow trout (RBT, Oncorhynhus mykiss). Rainbow trout are a model salmonid species that have undergone two additional rounds of whole genome duplication. There was limited expression of activin Ab in RBT embryos despite these genes exhibiting significantly elevated expression in post-hatch skeletal muscle. Divergent expression patterns were also observed for activin receptor type IIB ohnologs. CRISPR targeting of activin Aa2 and activin Ab2 did not identify any developmental or growth phenotypes in edited RBT, however, a high percentage of in-frame alleles were identified in activin Aa2 targeted fish. The research identifies mechanisms of specialization among the duplicated activin ohnologs across embryonic development and during periods of high muscle growth in larval and juvenile fish. The knowledge gained provides critical insights into viable gene-targeting approaches for engineering the activin receptor signaling pathway to improve physiological performance in salmonid species.