Epigenetics in a marine fish: Role of DNA methyltransferases in embryonic development

Neel Aluru, Biology
Sibel Karchner, Biology



  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.