Molecular basis of sex and reproductive status in breeding zebrafish

Abstract

The zebrafish ( Danio rerio) is used extensively as a model species for studies on vertebrate development and for assessing chemical effects on reproduction. Despite this, the molecular mechanisms controlling zebrafish reproduction are poorly understood. We analyzed the transcriptomic profiles of the gonads of individual zebrafish, using a 17k oligonucleotide microarray, to define the molecular basis of sex and reproductive status in sexually mature fish. The gonadal transcriptome differed substantially between sexes. Among the genes overexpressed in females, 11 biological processes were overrepresented including mitochondrion organization and biogenesis, and cell growth and/or maintenance. Among the genes overexpressed in males, six biological processes were overrepresented including protein biosynthesis and protein metabolism. Analysis of the expression of gene families known to be involved in reproduction identified a number of genes differentially expressed between ovaries and testes including a number of sox genes and genes belonging to the insulin-like growth factor and the activin-inhibin pathways. Real-time quantitative PCR confirmed the expression profiles for nine of the most differentially expressed genes and indicated that many transcripts are likely to be switched off in one of the sexes in the gonads of adult fish. Significant differences were seen between the gonad transcriptomes of individual reproductively active females reflecting their stage of maturation, whereas the testis transcriptomes were remarkably similar between individuals. In summary, we have identified molecular processes associated with (gonadal) sex specificity in breeding zebrafish and established a strong relationship between individual ovarian transcriptomes and reproductive status in females.

Sexual dimorphism in hepatic gene expression and the response to dietary carbohydrate manipulation in the zebrafish (Danio rerio)

“…In mammals, the liver is one of the most sexually dimorphic organs in terms of gene expression (Yang et al, 2007). Widespread sexual dimorphism in gene expression has previously been identified in analyses of brains in Atlantic salmon (Aubin-Horth et al, 2005) and whole zebrafish (Wen et al, 2005), and comparisons between ovaries and testes in mature zebrafish (Santos et al, 2007); however, to the best of our knowledge, extensive measures of hepatic sexual dimorphism have not been documented in any fish species.…”

“…As a result, sexual dimorphism may affect different hepatic functions related to glucose metabolism and metabolic phenotypes, and contribute to sex differences in physiology, homeostasis, and energy metabolism. Most studies of sexually dimorphic gene expression have occurred in mammals, and studies of sexual dimorphism in fish transcriptomes are rare [but see (Aubin-Horth et al, 2005;Wen et al, 2005;Santos et al, 2007)]. The extent of sexual dimorphism in the hepatic transcriptome and its resultant influence on physiological phenotypes are unknown in any fish species.…”

Endocrinology: Advances through omics and related technologies

“…One comparative transcriptomic approach of ovary versus testis revealed more than 3500 genes differentially expressed between the two organs with nearly 50 presenting a large difference in expression, suggesting gene silencing in one of the two sexes (Santos et al, 2007a). Also, while individual variability between mature males does not appear to influence testis transcriptomic pattern, ovaries have been found to have significant variation between individuals (Santos et al, 2007b). The zebrafish ovary is asynchronous, therefore the relative ratio of oogenesis stages across whole ovary is not stable and impacts transcriptomic patterns.…”

Probing the xeno-oestrogenic impact of sediment cores contaminated by the pulp and paper industry: induction of aromatase cyp19a1b in late larval zebrafish

“…In such species, the regulation of reproduction and associated endocrine processes are manipulated by feedback from endogenous steroid production and environmental factors together, including photoperiod, temperature, and chemical cues (Hill et al 2005). Gene transcription of key biomarkers associated with pathways of the hypothalamus-pitutary-gonadal (HPG) axis presents strong phenotypic anchoring of a hazardous chemical assault on teleostean species (Klaper et al 2006, Santos et al 2007). …”