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Open Access Research article

Differential gene expression in male and female rainbow trout embryos prior to the onset of gross morphological differentiation of the gonads

Matthew C Hale1*, Peng Xu1, Julie Scardina1, Paul A Wheeler2, Gary H Thorgaard2 and Krista M Nichols13

Author Affiliations

1 Department of Biological Sciences, Purdue University, West Lafayette, IN 47907,USA

2 School of Biological Sciences and Center for Reproductive Biology, Washington State University, Pullman, WA 99164, USA

3 Department of Forestry and Natural Resources, Purdue University, West Lafayette, IN 47907, USA

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BMC Genomics 2011, 12:404  doi:10.1186/1471-2164-12-404

Published: 8 August 2011

Abstract

Background

There are large differences between the sexes at the genetic level; these differences include heterogametic sex chromosomes and/or differences in expression of genes between the sexes. In rainbow trout (Oncorhynchus mykiss) qRT-PCR studies have found significant differences in expression of several candidate sex determining genes. However, these genes represent a very small fraction of the genome and research in other species suggests there are large portions of the transcriptome that are differentially expressed between the sexes. These differences are especially noticeable once gonad differentiation and maturation has occurred, but less is known at earlier stages of development. Here we use data from a microarray and qRT-PCR to identify genes differentially expressed between the sexes at three time points in pre-hatch embryos, prior to the known timing of sexual differentiation in this species.

Results

The microarray study revealed 883 differentially expressed features between the sexes with roughly equal numbers of male and female upregulated features across time points. Most of the differentially expressed genes on the microarray were not related to sex function, suggesting large scale differences in gene expression between the sexes are present early in development. Candidate gene analysis revealed sox9, DMRT1, Nr5a1 and wt1 were upregulated in males at some time points and foxl2, ovol1, fst and cyp19a1a were upregulated in females at some time points.

Conclusion

This is the first study to identify sexual dimorphism in expression of the genome during embryogenesis in any fish and demonstrates that transcriptional differences are present before the completion of gonadogenesis.

Keywords:
Sex-biased expression; ovary; testis; microarray; candidate genes