NOVEL INSIGHTS INTO MYOGENIC PRECURSOR CELL PHENOTYPES USING COMPARATIVE IN VITRO ANALYSES.

Zebrafish (Danio rerio) and giant danio (Devario aequipinnatus) represent comparative growth models, which provide valuable data for understanding of growth of commercially important fish species. These species exhibit two muscle growth paradigms, determinate (zebrafish) and indeterminate (giant danio), allowing for in depth investigation into pathways regulating muscle growth. Recent studies have shown that myogenic precursor cells (adult muscle cells) from these two species exhibit differential biomarkers and proliferation capacities (Fig. 1). The present study utilized a primary myogenic cell culture system to test the hypothesis that myogenic precursor cells exhibit growth paradigm specific phenotypes that are responsible for muscle growth potential in adult organisms.  

To test this, myogenic precursor cells for each species were isolated in tandem and cultured under the same conditions. Proliferating myoblasts were treated with several molecules to assess growth hormone, transforming growth factor, insulin and insulin-like growth factor pathways for 4 days. Cellular phenotype was measured by analyzing cell proliferation, cell differentiation, and gene expression changes between growth paradigms.  

Giant danio myogenic precursor cells exhibit greater proliferative capacity, in vitro, compared to zebrafish cells (Fig. 1a). Consistent with the proliferative data, zebrafish cells express higher levels of the myogenic lineage commitment marker myf5. Additionally, rainbow trout exhibit a high proliferative capacity in vitro, and lower myf5 levels (Fig. 1b), similar to giant danio. The expression of Pax-3 and -7 genes are also differentially regulated between growth paradigms and growth factors differentially regulate the growth pathways in a growth paradigm manner.

These data suggest that giant danio can serve as excellent model organisms for studies investigating muscle growth relevant to commercially important species that are larger and more cumbersome to rear in research laboratories. Additionally, these data suggest that myogenic precursor cell phenotype likely contributes to organismal growth potential.