THE INFLUENCE OF TEMPERATURE ON MESSENGER-RNA LEVELS FOR MUSCLE CONTRACTILE PROTEIN AND A PROTOONCOGENE ASSOCIATED WITH CELL-DIVISION IN ATLANTIC SALMON (SALMO-SALAR L)

In Atlantic salmon (Salmo salar L.) embryos, an increase in temperatur e from 5 to 8 or 11 degrees C causes, by the time of hatching, an incr ease in myofibrillar protein content and a reduction in nuclear prolif eration when compared with embryos raised at lower temperatures. This implies a shift in emphasis during embryonic development from nuclear hyperplasia to contractile protein accretion at higher temperatures. T he steady-state mRNA levels of proteins indicative of these processes were investigated. The proteins were actin, as a measure for myofibril lar protein, and cellular myc, as a measure for nuclear proliferation. Additionally a probe for myosin heavy chain was used. The mRNA levels for myofibrillar protein were not increased at the higher temperature , thus suggesting temperature-dependent translational or post-translat ional control. Actin and myosin heavy chain mRNA responses differed, s upporting the existence of temperature-dependent myosin heavy chain is oforms. The presence of c-myc mRNA in embryonic Atlantic salmon was sh own. The mRNA level of this nuclear proliferation marker was decreased at higher temperatures and could be related to histological data on n uclear numbers in embryonic salmon muscle.