Submitted to: Marine Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/22/2017
Publication Date: 6/3/2017
Citation: Koganti, P., Wang, J., Cleveland, B.M., Yao, J. 2017. 17ß-Estradiol increases non-CpG methylation in exon 1 of the rainbow trout (Oncorhynchus mykiss) MyoD gene. Marine Biotechnology. 19:1-7. doi:10.1007/s10126-017-9756-6.

Interpretive Summary: Muscle growth is reduced in sexually maturing rainbow trout to allow more energy to be devoted to gonad development. Estradiol is a female sex steroid that increases only during sexual maturation and is a hormonal signal responsible for reducing muscle growth. Estradiol partially exerts these effects by reducing expression of MyoD, a gene critical for muscle cell differentiation and muscle accretion. This study determined that estradiol increases methylation of bases within the MyoD gene, which likely leads to reduced MyoD expression. This process is defined as epigenetic regulation since it modifies the DNA without altering the genetic code itself. The enzymes that induce DNA methylation were also increased with estradiol treatment. These findings indicate that the estradiol regulates muscle growth partially through epigenetic-induced changes in MyoD expression, thereby identifying a novel mechanism affecting economically important traits.

Technical Abstract: CpH methylations are epigenetic markers enriched in stem cells which are lost during cell differentiation. DNMT3a and DNMT3b are de novo methyltransferases contributing to CpH methylations. MyoD is an important myogenic transcription factor necessary for the differentiation of myogenic precursor cells (MPC) to form mature myotubes, a process essential for muscle growth. Epigenetic markers such as CpH methylations are known gene regulators that are important for the differentiation process. Here we determine whether DNA methylation is a potential mechanism associated with the ability of 17ß-estradiol (E2) to reduce MyoD expression and muscle growth in rainbow trout (Oncorhynchus mykiss). Rainbow trout received a single intraperitoneal injection of E2 or the injection vehicle (control). Skeletal muscle was collected 24 hr post-injection and analyzed for DNA methylation within the MyoD gene and expression of DNA methyltransferases. CpG islands of the MyoD gene were predicted using MethPrimer software and these regions were PCR amplified and analyzed using bisulfite sequencing. The percent methylation of the targeted CpG did not differ between control and E2-treated fish. However, percent CpH methylations in MyoD exon 1 were elevated with E2 treatment. Two of these CpH methylations were present in conserved motifs, Estrogen Response Element (ERE) and MYC. Quantitative real time RT-PCR analysis revealed a significant increase in expression of DNA methyltransferases (DNMT3a and DNM3b) in E2-treated muscle, suggesting an increased capacity for de novo methyltransferase. Differential levels of CpH methylation in the MyoD gene of control and E2-treated fish suggests an epigenetic mechanism through which E2 decreases expression of MyoD and contributes to reduced muscle growth.