Changes in gene expression during follicle maturation in rainbow trout Oncorhynchus mykiss

Authors: Weber, Gregory - Greg; Ma, Hao; HOFF DE SOUZA, CARLOS - Embrapa; Leeds, Timothy - Tim; Gao, Guangtu

Submitted to: Aquaculture America Conference
Publication Type: Abstract Only
Publication Acceptance Date: 10/5/2015
Publication Date: 2/22/2016
Citation: Weber, G.M., Ma, H., Hoff De Souza, C.J., Leeds, T.D., Gao, G. 2016. Changes in gene expression during follicle maturation in rainbow trout Oncorhynchus mykiss [abstract]. Aquaculture America Conference. p. 19.

Interpretive Summary:

Technical Abstract: Failure to successfully complete ovarian follicle maturation is one of the most common reproductive problems in captive female broodstock, often requiring the use of reproductive assistance technologies. An improved understanding of how requisite environmental and social conditions translate into neuroendocrine signals leading to successful production of quality eggs, and what constitutes a high quality egg or ovum, have been the focus of much research. We observed poor eyeing rate in our broodstock is associated with a prolonged progression through follicle maturation. Eyeing rate for offspring of those females whose oocytes had completed yolk-vesicle fusion, indicated by a dramatic decrease in echogenicity, over a week before ovulation, was less than half of that for offspring of females that ovulated within about 1 week of completing yolk-vesicle fusion. This observation suggests that not only must oocytes complete maturation; they must do so in a timely manner. Previous studies have identified many transcripts in the oocyte and the surrounding somatic follicle cells that change expression during follicle maturation in rainbow trout. Differential expression of some of these transcripts has been associated with differences in egg quality. There is still much work to be done in all aspects of this area of research including associating differences in expression patterns that associate with variation in egg quality with the causes of those disparate expression patterns. Our goal is to examine changes in expression during maturation in rainbow trout follicles both in vivo and in response to hormones in vitro to identify patterns of transcript expression associated with failed maturation and poor egg quality. We are using multiplex analysis and RNA-seq to identify transcripts of possible interest. Among many transcripts that have been identified as associating with follicle maturation we have found expression of fshr, bambi, inhibin-beta-a, star, and shgbb, to consistently exhibit significant changes in expression with in vivo and in vitro maturation. We then treated oocytes with the maturation inducing steroid (MIH; 17a20bdihydroxy-4-pregnen-3-one) and salmon pituitary extract and compared expression among treatments by RNA-seq analysis in eggs confirmed with RT-qPCR analysis to exhibit these typical responses. Although the changes in transcripts during follicle maturation were consistent between multiplex analysis and RNA-seq analysis, the transcripts in the multiplex were not among those most strongly responsive to the hormone treatments as measured by RNA-seq analysis. We are now investigating these more highly regulated transcripts. As an example, two among the more highly expressed are serine threonine-protein kinase sgk2 and sgk1 isoforms. Preliminary in vitro studies using RT-qPCR analysis confirm this response, and an inhibitor of SGK activity, GSK 650394, was shown to inhibit MIH-induced germinal vesicle breakdown, a marker for the resumption of meiosis during oocyte maturation. Yet to be determined are the function of these highly responsive transcripts in the follicle or developing embryo, and if differential expression of these transcripts associate with egg quality.