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°C than at either 10 or 15°C. Over a period of 7 d, there was a gradual reduction in the number of TNT isoforms, but the pattern in 5°C larvae after 7 d still did not resemble that in 1 d-old larvae reared at 15°C.