DEVELOPMENTAL-CHANGES IN THE COMPOSITION OF MYOFIBRILLAR PROTEINS IN THE SWIMMING MUSCLES OF ATLANTIC HERRING, CLUPEA- HARENGUS

Changes in myofibrillar protein composition during development have been investigated in the swimming muscles of the Atlantic herring Clupea harengus L. using a range of electrophoretic techniques. The main muscle-fibre type of larvae, and the fast- and slow-muscle fibres of adult fish were found to contain distinct isoforms of myosin heavy chain (MHC) and myosin light chain 2 (LC2). Larval LC2 was present as a minor component of adult fast-muscle myosin. In contrast, larval and adult fast-muscle myosin appeared to contain identical alkali light chains. Tropomyosin and troponin C were also identical in larval and in adult fast-muscle. All three muscle-fibre types contained unique isoforms of troponin T (TNT) and troponin I (TNI). Larval muscle had multiple isoforms of TNT, some of which may correspond to embryonic forms. It was concluded that although the main muscle-fibre type in larvae shares some myofibrillar proteins with adult fast muscle, it also contains characteristic isoforms of MHC, TNI, TNT and LC2 and therefore represents a distinct fibre type. The particular combination of myofibrillar proteins present at any developmental stage was found to be dependent on the rearing temperature. For example, a higher proportion of embryonic TNT isoforms were present at hatching in larvae reared at 5-degrees-C than at either 10 or 15-degrees-C. Over a period of 7 d, there was a gradual reduction in the number of TNT isoforms, but the pattern in 5-degrees-C larvae after 7 d still did not resemble that in 1 d-old larvae reared at 15-degrees-C.