Epigentic Landscapes In A Marine Mollusc: What DNA Methylation Patterns Tell Us About Gene Regulation In The Pacific Oyster (Crassostrea gigas)

DNA methylation has been well studied in plants and mammals where it’s been shown to play an important role in hybrid vigor and the regulation of genes contributing to commercially important traits.  However, the same level of research has not been extended to invertebrates and surprisingly little is known about this mechanism in these taxa, particularly mollsucs.  Previously, we have applied in silico approaches to characterize DNA methylation in Pacific oysters (Crassostrea gigas).  Our results suggest that DNA methylation has regulatory functions in C. gigas, particularly in gene families that have inducible expression, including those involved in stress and environmental responses. To gain further insight into how DNA methylation may support the regulation of genes in C. gigas, we are using a combination of methylation enrichment and high-throughput bisulfite sequencing to map DNA methylation at high-resolution at thousands of individual cytosine loci.  Results are consistent with previous in silico analysis indicating that genes with differing regulatory requirements are differentially methylated.  Specifically, we find that ubiquitously expressed genes, such as those involved in basic metabolic functions, have the highest amount of methylation, whereas genes with tissue-specific or inducible expression have a significantly less methylation. We are analyzing this data at a finer scale to facilitate the identification of patterns of methylation in various genomic regions including; exons, introns, promoters, and transposable elements. Results of these analyses will be presented and broader implications, in terms of applications in aquaculture and ecology, will be discussed.