Myosin, parvalbumin and myofibril expression in barbel (Barbus barbus L.) lateral white muscle during development.

Histo- and immunohistochemical techniques have recently been used to study the fibre type and myosin expression in fish muscle during development. In the present work, embryonic, larval and adult myosin isozymes (heavy and light chains) and parvalbumin isotypes were analyzed, from fertization to the adult stage, by polyacrylamide gel electrophoresis of barbel (Barbus barbus L.) trunk muscle extracts. The examined myosins display the sequential transitions from embryonic to larval and adult forms characteristic of higher vertebrates. They are characterized by specific heavy chains but their light chains differ only by the LC1/LC3 stoichiometry with LC3 exceeding LC1 after 10 days. Sarcoplasmic parvalbumins show considerable and unforeseen developmental transitions in their isotype distribution: the PA II isotype first appears after hatching and becomes the predominant form until the length reaches about 6 cm. One month after hatching, the amount of PA II then decreases and the synthesis of PA III and IV further increases to reach the typical adult pattern at a size of 18 cm. These observations show that the distribution of parvalbumin isotypes reflects the stage of development. It suggests a specific role for each isotype in relation to muscle activity. Microscopy illustrates the progressive development of somites, muscles cells, and myofibrils, which accelerates at hatching when movements increase.