Epigenetics in a marine fish: Role of DNA methyltransferases in embryonic development
Neel Aluru, Biology
Sibel Karchner, Biology
Abstract
Animals adapt to their environment through alterations in morphological, behavioral or reproductive phenotypes. These phenotypic responses to environmental changes are explained in part by genetic mechanisms. However, recent studies have demonstrated that in addition to genetic mechanisms, epigenetic mechanisms might be involved in environmental adaptations. For example, marine fish such as sea bass exhibit temperature-induced sex determination, where higher temperatures result in a larger number of male embryos through an increase in DNA-methylation.
Epigenetics involves changes in gene expression without alteration of the DNA sequence. The main epigenetic mechanisms that are critical for gene expression include DNA methylation, chromatin modifications and non-coding RNAs. DNA methylation involves covalent modification of a cytosine nucleotide by the addition of a methyl group when cytosine occurs next to a guanine nucleotide. This addition of a methyl group is catalyzed by a group of enzymes called DNA methyltransferases (DNMTs). DNMTs are essential for normal development, and aberrant DNA methylation is linked to severe developmental deformities and in some cases mortality. High levels of DNA methylation is associated with silencing of gene expression, whereas reduced methylation is linked to active gene transcription. Even though the implications of DNA methylation are well known, the fundamental understanding of the functioning of DNMTs in marine species is lacking. Interestingly, a higher overall methylation level has been observed in fish, especially in polar fishes, compared to mammals and birds, and this is attributed to differences in body temperature. In contrast to mammals, some freshwater fish possess multiple copies of DNMT genes due to genome duplication events. However, the biological significance of these multiple DNMT genes is unknown.
The main goal of this project is to identify and characterize the DNMT genes in the estuarine killifish, Fundulus heteroclitus, and determine their expression patterns during development, as well as tissue-specific expression in adults. Killifish is an excellent marine model species that displays a variety of physiological adaptations to its environment, and for which genomic tools are available. Understanding the mechanisms associated with these adaptations in a marine species will shed light on the effects of environmental change on coastal and ocean life, as well as providing information on the molecular biodiversity that exists in marine systems. Therefore, this project addresses important questions relevant to the research missions of both COI and OLI. These results will form the basis for future studies in characterizing the function of these genes using molecular and biochemical approaches, and create future funding opportunities from federal agencies such as NSF.