Switches in fish myosin genes induced by environment temperature in muscle of the carp.
Fish are cold blooded animals and their muscle function is expected to be greatly affected by environmental temperature. Species that live in the Antarctic ocean have evolved a different contractile system to fish that live in the tropical waters. In the case of Antarctic fish they have a higher specific myofibrillar ATPase activity but 'the trade off' seems to be a lower thermal stability. They are thus capable of a greater muscle power output at low temperatures but the lower thermal stability means they are restricted to living at temperatures below +4 degrees C. Some species, however, experience a wide range of seasonal variations in temperature. We found that these species adapt by changing their myofibrillar apparatus so that they have a higher specific ATPase which physiological studies indicate is due to a different type of myosin crossbridge for low temperature swimming. This is reversible and they develop a contractile system with a greater thermal stability and a commensurate loss of ATPase activity when their environment warms up again. There were several possibilities by which this may be achieved including expression of different isoform genes or the post- translational processing of existing proteins. To elucidate the mechanism we made a carp genomic library and screened this for myosin heavy chain gene using mammalian cDNA sequences under moderate stringency conditions. The clones were restriction mapped which resulted in 28 non overlapping sequences. This indicated that the carp had a reasonably large family of myosin heavy chain genes that is about twice the size of that in mammals. Rather fortuitously the first sequence to be identified was from the gene that is predominantly expressed in white muscle at warm temperatures. This was done by extracting the RNA from red and white muscle of fish acclimated to different 25 degrees C, 18 degrees C or 8 degrees C and carrying out Northern analysis using the gene fragment as the probe. The time course for the expression of this gene when carp maintained at a low temperature were acclimated to a warm temperature was slightly in advance of the change in myofibrillar ATPase which suggested that this strategy for adaptation is regulated at the transcriptional level. Hence these species of fish can adapt to seasonal changes in temperature by expressing different myosin heavy chain isoform genes and rebuilding their myofibrils for either warm or cold temperature swimming. At the present time we are characterising the 5' regulatory (promoter) sequence of this gene to see how a temperature switch may operate.(ABSTRACT TRUNCATED AT 400 WORDS)
Goldspink
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Unit of Veterinary Molecular and Cellular Biology, Royal Veterinary College, University of London.
Turay
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Hansen
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Ennion
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S
Gerlach
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G
D000222:Adaptation, Physiological / Q000235:genetics; D000818:Animals; D015152:Blotting, Northern; D002347:Carps / Q000235:genetics*; D009119:Muscle Contraction / Q000502:physiology; D009132:Muscles / Q000502:physiology*; D009218:Myosins / Q000235:genetics*; D011499:Protein Processing, Post-Translational / Q000502:physiology; D015183:Restriction Mapping; D013696:Temperature; D014158:Transcription, Genetic / Q000502:physiology
D009218:Myosins