Epigenomic and transcriptomic alterations of channel catfish exposed to DNA methyltransferase inhibitor and estradiol
Type of DegreePhD Dissertation
School of Fisheries, Aquaculture, and Aquatic Sciences
MetadataShow full item record
Teleost fish exhibit a great level of diversity of sex determination. With channel catfish (Ictalurus punctatus), a lower teleost, sex determination genes have not been identified. However, the sex determination region (SDR) was found to be differentially methylated between the X- and Y-alleles, with the Y-alleles being hypomethylated, suggesting that methylation may be involved in sex determination in channel catfish. We tested the effect of a methylation inhibitor, 5-aza-2’-deoxycytidine (5-aza-dC), on whole genome methylation and sex differentiation. 5-aza-dC caused genome-wide reduction of DNA methylation, with the largest reduction in females, and led to sex reversal from genetic females to phenotypic males. Whole genome bisulfate sequencing (WGBS) and RNA-Seq analysis revealed that methylation levels in the SDR were significantly reduced, especially in females, and a set of genes were sex-specific differentially expressed in females, including seven genes, hydin, spred3, slitrk3, tsnaxip1, carmil2, sphkap, and hsf4, that were up-regulated, and three genes, esrrg, pard6a, and actrt3, that were down-regulated in females. Taken together, this work provided a direct evidence for the involvement of methylation in sex determination in channel catfish. It was possible that demethylation in the sex determination region resulted in expression of key gene(s), such as hydin, for differentiation into males, which in turn activating expression of a set of genes that “slow-down” sex differentiation into females, leading to sex reversal from genetic females to phenotypic males. Exogenous estrogen 17β-estradiol (E2) has been shown to effectively induce feminization in teleosts. However, the molecular mechanisms underlying the process remain unclear. Here, we determined global DNA methylation and gene expression profiles of channel catfish during early sex differentiation after E2 treatment. Overall, the levels of global DNA methylation after E2 treatment were not significantly different from those of controls. However, a specific set of genes were differentially methylated, which involved in many sex differentiation-related pathways, such as MARK signaling, adrenergic signaling, Wnt signaling, GnRH signaling, ErbB signaling, and ECM-receptor interactions. Many genes involved in these pathways were also differentially expressed after E2 treatment. Specifically, E2 treatments resulted in upregulation of female-related genes and downregulation of male-related genes in genetic males during sex reversal. However, E2-induced sex reversal did not cause sex-specific changes in methylation profiles or gene expression within the sex determination region (SDR), although expression of over a dozen of genes were mostly up-regulated after E2 treatment, especially at 16 days post fertilization (dpf), suggesting that E2-induced sex reversal was a downstream process independent of the sex determination process that was dependent on sex-specific methylation within the SDR.