Phenotypic plasticity of the fast skeletal muscle in response to short and long temperature acclimation in the goldfish (Carassius auratus).

Phenotype is the result of the interaction between genotype and environment. Through the integration of environmental cues a single genotype can display different phenotypes in order to adapt a changeable environment, a process known as phenotypic plasticity. Temperature is considered one of the major abiotic factors driving phenotypic plasticity in fish skeletal muscle. Phenotypic plasticity induced by temperature in skeletal muscle is observed at different biological levels from gene expression to remodelling of the skeletal muscle fibre structure. In the present study we used the goldfish (Carassius auratus) as a model to study how short (4 weeks) and long (12 weeks) acclimation periods to different temperatures modify muscle fibre nuclei content and the transcript abundance of three key sarcomere components: myosin heavy chains (myhc), myosin light chains (myl) and the troponin subunit I (tnni). We identified several myh (11), myl (10) and tnni (10) isoforms with significant changes in transcription in response to acclimation for some of the components analysed. We found three myhIIa isoforms strongly regulated by acclimation temperature, where myhIIa.1 increased transcription in response to low temperatures (<8oC), myhIIa.2 increased at 15oC and myhIIa.3 increased when temperature was >28oC. Similarly myl2, myl3, myl1b and tnni2a3 transcription was response to temperature, showing a full response when temperature was =15oC. In parallel, muscle fibre nuclei content increased with temperature, with differences observed even after short acclimation. Changes in expression profiles of key sarcomeric components are likely to be part of a metabolic compensation process in response to temperature and maintain an efficient skeletal muscle contraction. Similarly, changes in nuclei content could be part of the response to changes in ion leakage through the skeletal muscle membrane originated by temrpeature in order to maintain the membrane potential. Our results also show that it is not necessary to have along period acclimation to start to observe significant differences in nuclei content and gene expression.