GENOMICS AND BIOINFORMATICS RESEARCH IN AGRICULTURALLY IMPORTANT ORGANISMS
Location: Genomics and Bioinformatics Research Unit
Title: Benzo(A)pyrene induced glycine N-methyltransferase messenger rna expression in Fundulus heteroclitus embryos
Submitted to: Marine Environmental Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 21, 2009
Publication Date: October 1, 2010
Citation: Fang, X., Dong, W., Thornton, C., Scheffler, B.E., Willet, K. 2010. Benzo(A)pyrene induced glycine N-methyltransferase messenger rna expression in Fundulus heteroclitus embryos. Marine Environmental Research. 69:274-276.
Interpretive Summary: Fundulus is an important model species in marine environmental toxicology experiments and Glycine N-methyltransferase (GNMT) is critically involved in regulation of DNA methylation thus having an effect on gene expression. In this manuscript we have characterized the expression of the GNMT in fertilized and unfertilized embryos, with and without exposure of the hydrocarbon benzo(a)pyrene (BaP). GNMT expression was reduced in more developed embryos. Exposure of high levels of BaP increased GNMT indicating that BaP may alter gene expression of an important gene involved in DNA methylation.
Glycine N-methyltransferase (GNMT) is a mediator in the methionine and folate cycles, and is responsible for the transfer of a methyl group from S-adenosylmethionine (SAM) to glycine forming S-adenosylhomocysteine (SAH) and sarcosine. All the known DNA methyltransferases use SAM as a methyl donor thus, GNMT is critically involved in regulation of DNA methylation. Altered GNMT activities have been associated with liver pathologies including hepatocellular carcinoma. The homotetramer form of GNMT is enzymatically active, but the homodimeric form has been suggested as the 4S PAH-binding protein which may mediate CYP1A expression. To further understand the role of GNMT in benzo(a)pyrene (BaP)-related toxicity, full length Fundulus heteroclitus GNMT cDNA was cloned from adult liver. The open reading frame (ORF) of GNMT is 888 base pairs long and encodes a deduced protein of 295 amino acids which is 74% similar to human GNMT. Expression of GNMT mRNA was determined by quantitative RT-PCR. In unfertilized, 2 day postfertilization (dpf), and 3 dpf embryos GNMT was constitutively higher than in 4, 7, 10 or 14 dpf embryos. Embryos were exposed to waterborne BaP at 10 and 100 mg/L, and by 10 dpf the higher BaP dose caused increased expression of GNMT mRNA. These results suggest that PAH exposure may alter expression of an important physiological methylation mediator. Future work will be necessary to determine enzyme level effects of BaP exposure as well.