NON-CpG METHYLATION IN THE FIRST EXON OF THE MYOGENIC TRANSCRIPTION FACTOR MyoD IN RAINBOW TROUT MUSCLE IS AFFECTED BY ESTROGEN

Prasanthi P. Koganti*, Jian Wang, Beth Cleveland, Gregory M. Weber, and Jianbo Yao
 
Division of Animal and Nutritional Sciences
West Virginia University
Morgantown, WV 26505
ppkoganti@mix.wvu.edu

Estrogen is released during sexual maturation in fish, which contributes to muscle degradation thereby affecting the process of myogenesis. Myogenesis starts with activation of myosatellite cells that lie between the basal lamina and sarcolemma of mature muscle fibers. The activated myosatellite cells proliferate and differentiate into mature muscle. This mechanism is governed by different signaling pathways, epigenetic and myogenic regulatory factors. Myoblast determination protein 1 (MyoD), a basic helix loop helix transcription factor, is a master regulator of muscle cell differentiation. The aim of the present study was to understand the effects of estrogen on the epigenetic regulation of MyoD gene at DNA level in rainbow trout.

Fish were treated with either estrogen (5 µg/g body weight, test group) or vehicle (control group). PCR primers were designed to amplify the predicted CpG islands in exon 1 of the MyoD gene (Fig. 1). Genomic DNA and RNA were isolated from the skeletal muscles of both groups. DNA was bisulfite treated, PCR amplified and sequenced using Illumina sequencing technology. The results showed that methylations on the CpG sites are not significantly different between the two groups. However, significantly increased methylations in four non-CpG sites (methylated cytosine not followed by guanine but by cytosine, adenine and thymine) in CpG island 1 were observed in the estrogen treated group compared to the control group (Fig. 2). In addition, quantitative real time PCR analysis revealed differential expression of the myogenic regulatory factors (Pax7 and MyoD) between the two groups. Pax7 expression was increased while MyoD expression was decreased in the estrogen treated group compared to the control group (p-value < 0.05). Collectively, the results indicate that estrogen maintains the myosatellite cells in proliferative and/or undifferentiated states partly through epigenetic regulation of MyoD.