Abstract
The paired box-7 (pax7) transcription factor expressed in satellite cells (SCs) is an essential regulator of skeletal muscle growth and regeneration in vertebrates including fish. Characterization of rainbow trout (Oncorhynchus mykiss) pax7 gene/s may offer novel insights into skeletal myogenesis by SCs in this indeterminate growth species. Further, evaluation of promoters for cis-regulatory regions may shed light on the evolutionary fate of the duplicated genes. Employing standard PCR, cloning and computational approach, we identified and report complete coding sequences of two pax7 paralogs of rainbow trout (rt); rtpax7α and rtpax7β. Both genes show significant identity in the nucleotide (97%) and the predicted amino acid (98%) sequences, and bear the characteristic paired domain (PD), octapeptide (OP) and homeodomain (HD) motifs. We further report several splice variants of each gene and nucleotide differences in coding sequence that predicts six putative amino acid changes between the two genes. Additionally, we noted a trinucleotide deletion in rtpax7β that results in putative serine elimination at the N-terminus and a single nucleotide polymorphism (SNP) in majority of the rtpax7β variants (6/10) that predicts an arginine substitution for a lysine. We also deciphered the genomic organization up to the first three exons and the upstream putative promoter regions of both genes. Comparative in silico analysis of both the trout pax7 promoters with that of zebrafish pax7 duplicates; zfpax7a and zfpax7b; predicts several important cis-elements/transcription factor binding sites (TFBS) in these teleost pax7 promoter regions.
Highlights
Growth and regeneration of skeletal muscle in vertebrates is mainly attributed to mitotically proficient adult muscle stem cells termed satellite cells (SCs) (Lepper et al 2011; Moss and Leblond 1971; Motohashi and Asakura 2014; White et al 2010)
Analyses of pattern identification using Prosite revealed the presence of conserved features in both putative protein forms that are characteristic of Pax7 protein; paired domain (PD), homeodomain (HD) and an octapeptide (OP) (Figure 1)
A pairwise comparison of the nucleotide sequences showed that both forms share 83% identity in the 5′-untranslated region (UTR) sequences, while the protein coding sequences share 97% identity
Summary
Growth and regeneration of skeletal muscle in vertebrates is mainly attributed to mitotically proficient adult muscle stem cells termed satellite cells (SCs) (Lepper et al 2011; Moss and Leblond 1971; Motohashi and Asakura 2014; White et al 2010). While the myogenic program of SCs is primarily driven by myogenic regulatory factors (Megeney et al 1996; Montarras et al 2000; Smith et al 1994), their maintenance, propagation and self-renewal in growing muscle have been attributed to the expression of pax (Oustanina et al 2004; Seale et al 2004). The functional significance of pax in the physiology of SCs is primarily understood through studies conducted in knock-out mice (Kuang et al 2006; Oustanina et al 2004; Relaix et al 2006; Seale et al 2004).
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