The effects of CpG densities around transcription start sites on sex-biased gene expression in Poecilia reticulata

Abstract

As most genes are shared between females and males, DNA methylation is assumed to play a crucial role in sex-biased gene expression. DNA methylation exclusively occurs at CpG dinucleotides, and therefore, we would expect that CpG density around transcription start sites (TSSs) relate to sex-biased gene expression. Here we investigated the relationship between CpG densities around TSSs and the ratio of gene expression levels between sexes in the guppy (Poecilia reticulata),which displays remarkable sexual dimorphisms.Wefound that geneswithsex-biasedgeneexpressionhaddifferentCpGdensitiesdownstreamof TSSs comparedwith genes lacking sex-biased gene expression. Intriguingly,male-biased expression geneswith intermediateCpGdensity downstream of TSSs exhibited greater differences in gene expression between sexes in the gonad and tail.Our findings suggested the possibility that CpGs around TSSs, especially in the downstream regions, play a crucial role in sex-biased gene expression throughDNAmethylation.