Meeting Abstract
A major milestone in the evolution of complex multicellularity, division of labor by cell differentiation requires differential gene expression; the underlying epigenetic programs establish and maintain the differential expression through the cell cycle. Methylation of cytosines provides one component of the epigenetic equipment in some metazoans, but not others, and plays an important role in inheritance beyond the level of four bases across generation, and is thus crucial for understanding the evolution of complex multicellularity. Here we examine the complex life history of Aurelia a medusa bearing cnidarian, sister to the better studied Bilateral. Aurelia sp.1 exhibits complexity such as neurosensory organs, and a multistage life history where germ layers undergo complete reorganization and cells dedifferentiate and redifferentiate. To reveal changes in epigenetic programs throughout its life history, we sequenced cytosine methylation by whole genome bisulfite sequencing at various stages of Aurelia. We show that methylation is concentrated to CG sites; about 5% of CG sites are methylated in polyp. We also examine developmental genes such as transcription factors in the POU and SIX families that are known to be involved in neurosensory system development, and correlate methylation status with transcription level. We identify highly methylated regions across the genome, and assess these by sequence and gene ontology analysis. Overall, this study provides insight into the epigenetic regulation of gene expression through DNA methylation in a cnidarian that shows complex life history. This strengthens the case for evolutionary loss of DNA methylation in some bilaterians and supports aspects of shared ancestry in DNA methylation of Metazoa.
