LILLEY, T. R.*; MEDLER, S.; MYKLES, D. L.; Colorado State Univ.; Univ. at Buffalo; Colorado State Univ.: Lobster myocyte enhancing factor (Mef2): cloning and tissue expression in response to elevated ecdysteroid

Myocyte enhancing factor (Mef2) is a member of the MADS family of transcription factors. In mammalian skeletal muscles, it is involved in the transformation of fast fibers to slow fibers in response to sustained contractile activity. Mef2 is one of the factors that drive the expression of slow myofibrillar proteins to maintain the slow fiber phenotype. Our hypothesis is that Mef2 has a similar role in determining fiber phenotype in crustacean muscle. RT-PCR cloning was used to obtain a partial cDNA encoding lobster (Homarus americanus) Mef2. PCR was used to amplify a 138 bp highly conserved sequence in the DNA-binding domain of Mef2, located 54 bp from the start of the 5́ coding region. Qualitative PCR and real-time PCR were used to examine the tissue distribution of Mef2, as well as the effects of elevated ecdysteroid on Mef2 expression. As expected, Mef2 was expressed at high levels in skeletal muscles and intestine (which has a muscles for peristalsis); it was not expressed in heart, digestive gland, ovary, gill, and ventral nerve cord. Unlike mammals, there was no significant difference in Mef2 mRNA between slow and fast muscles. Mef2 expression was inversely proportional to hemolymph ecdysteroid concentration. These results do not support the hypothesis that Mef2 up-regulation is required to maintain the slow phenotype. However, the data indicate that an effect of molting is the suppression of Mef2-regulated genes in skeletal muscle regardless of phenotype. Supported by NSF (IBN-0077422).