Figure 8

Schematic representation of muscle ontogeny in halibut during metamorphosis; Schematic representation of the muscle ontogeny in halibut from larvae (stg 5) to juvenile (stg 10) and the overall expression pattern of halibut TnT genes. There is a general increase in myotome volume during metamorphosis. Note that throughout muscle ontogeny, prior to and after metamorphosis, symmetry is maintained both in the sagital and longitudinal planes. In pre-metamorphic halibut (stg 5 and 6) white muscle hyperplasic small diameter fibers are located in the most apical and lateral sides of the myotome regions (insert) which predominantly express efTnThh (black dots). As white muscle fibers increase in size the expression of fTnThh isoforms disappears. The expression of the other fTnThh isoforms (light grey dots) co-localizes with efTnThh expression up until stg 7. When the animals reach the beginning of metamorphosis (stg 7) all mature white muscle fibers express fTnThh-1 and -2 isoforms (light grey shading) and efTnThh is only found in smaller diameter hyperplasic fibers in the periphery of the myotomes around the myosepta (black dots). As the animals enter the climax of metamorphosis expression of the low molecular weight fTnThh isoforms is located in the entire myotome (light grey shading) and efTnThh is confined to scattered presumptive satellite cells (black dots). At climax (stg 9) and in juvenile (stg 10) white muscle fTnThh-1 and -2 isoforms are expressed in all the myotome with varying intensity and in fibers close to the myosepta expression is higher. In pre-metamorphic halibut red muscle (dark grey) all cells express sTnT2hh and AfTnThh. The expression of the red muscle specific Troponin T genes is constant and restricted to the outer red muscle throughout halibut metamorphosis and in juvenile animals.