Search

Aquatic animals are subject to varying degrees of starvation stress in their natural habitats due to food limitations. Consequently, starvation is a crucial environmental factor for sex determination in many species; however, limited research has been conducted on the effects of starvation on sex determination in shellfish. Here, four full sibling families of Pacific oysters were established and subjected to starvation stress. The results demonstrated that starvation caused the sex ratio (female to male) to change from 1:0.78 to 1:1.44 and resulted in a delay in gonadal development. Further studies revealed that the expression levels of DNA methylation-related genes Dnmt1 (DNA methyltransferase 1), Dnmt3a /b (DNA methyltransferase 3a/b) and Tet3 (tet methylcytosine dioxygenase 3) decreased under starvation stress. Conversely, the upregulation of Dmrt1 (doublesex and mab-3 related transcription factor 1), a gene typically associated with males, in females suggests that the increased proportion of males may be linked to starvation-induced high expression of this particular gene. In addition, the gene Dgkd (diacylglycerol kinase delta), which is involved in the regulation of second messenger protein kinase C, was differentially methylated between males and females, with the methylation level of this gene gradually increasing with male development, while the methylation level of this gene decreased under starvation stress. Correlation analysis of Dgkd methylation levels with expression levels showed a negative correlation between DNA methylation and gene expression. Finally dual fluorescence reporter experiments confirmed that DNA methylation suppressed Dgkd expression in vitro. In summary, the results suggest that starvation may regulate Dgkd gene expression through DNA methylation and thus affect Dmrt1 expression, thereby causing sex reversal in the Pacific oyster. The outcomes resolved how environmental factors are involved in sex reversal from an epigenetic perspective and provided a theoretical basis for sex control breeding in the Pacific oyster. [Display omitted] • Starvation stress causes male bias and delayed gonadal development in the oyster. • Starvation stress alters the expression of sex-associated genes Foxl2 , Dmrt1 and Dgkd in the oyster. • Sex bias is associated with DNA methylation in response to starvation stress. [ABSTRACT FROM AUTHOR]

The Pacific oyster (Crassostrea gigas), as the most productive cultured shellfish in the world, has considerable economic importance and value. Yet research on its sex determination remains lacking. Here, a novel HMG-box-containing homolog of the sox gene was uncovered in C. gigas (named CgSox-like). Alignment with the HMG-box of sox genes from other animals revealed that CgSox-like had a high similarity to the Sox gene of scallops. Among different adult tissues, CgSox-like was mainly expressed in the gonads. qPCR analysis revealed that CgSox-like and CgSox8 , a sox gene family gene mainly expressed in male gonads, shared similar expression patterns, with elevated expression as the male gonads developed. RNA interference and dual luciferase reporter assays demonstrated that CgSox-like was located upstream of CgSox8 and promoted the expression of CgSox8. In addition, analysis of CgSox-like and CgSox8 methylation patterns indicated that both genes were in hypomethylation state during the gonadal development. Finally, demethylase inhibitors resulted in elevated expression levels of CgSox-like and CgSox8 genes, suggesting that epigenetics was engaged in modulating the expression of sex-related genes in the Pacific oyster. Taken together, the novel gene CgSox-like was implicated in the sex determination or gonadal development process in male oysters. These results will provide valuable information for the investigation of sex determination mechanism and sex control breeding. • CgSox-like is involved in sex determination or gonadal development in oysters. • CgSox-like was located upstream of CgSox8 and promoted the expression of CgSox8. • DNA methylation participates in the regulation of sex determination in Crassostrea gigas. [ABSTRACT FROM AUTHOR]