Teleost fish exhibit a wide range of reproductive strategies, including the ability to change sex. Although sex steroids, neuropeptides, and the hypothalamic-pituitary-gonadal axis are well-studied in vertebrate reproduction, comparatively little is known about the mechanisms that regulate sex change. The purpose of the proposed study is to investigate gene expression changes during sex change in a protogynous (female to male change) teleost fish, the black sea bass (Centropristis striata). Using a whole transcriptomics approach, brain and gonad mRNAs will be sequenced from male, female, and sex-changing individuals, and compared using RNA-seq. Additionally, black sea bass will also be exposed to an aromatase inhibitor, exemestane, to decrease estrogen production and induce sex reversal. Gene expression patterns will be compared between natural and induced sex-changing fish. Most of the preliminary work for this study has already been completed, including fish sampling and transcriptome sequencing. For the proposed project, de novo transcriptome assemblies and RNA-seq will be completed, as well as real time quantitative PCR (qPCR) comparisons of selected genes between natural and induced sex change. A greater understanding of sex change may provide novel insights into vertebrate reproduction, and may be applied to understanding brain and gonadal reproductive processes in biomedical model organisms, such as the zebrafish (Danio rerio).
This research may provide more information to further understand reproduction in a variety of vertebrate taxa, including well-established models, such as zebrafish, mice, and humans. For example, our prior work in fish identified a novel G protein-coupled receptor family expression pattern (SREBs) in ovarian tissue, which previously, was only studied in the human brain (Breton et al. 2012, Matsumoto et al. 2000, 2008). This demonstrates that more information, in a variety of organisms, can provide greater insight into gene functions. Similarly, many novel genes, with little to no current research focus in vertebrate models, have already been observed in preliminary sequence analyses of the black sea bass brain transcriptome. Further study into these genes, and their roles in sex change and reproductive processes, will provide new foundational information in vertebrate reproduction that could be applied to future functional studies in controlling sex change, or evaluating reproductive effects in EDC models. The proposed project also represents an opportunity to provide undergraduate students in western Maine with experience in molecular biology approaches (RNA extractions, qPCR, and bioinformatics tools) that will enable them to develop interests and pursue careers in bioinformatics or biomedical research.
Additionally, exemestane used in the proposed research for inducing sex change in fish is classified as a third generation steroidal aromatase inhibitor used in breast cancer treatments in postmenopausal women (Geisler et al. 1998, Ruskana et al. 2010, Goss et al. 2011). Exemestane is commercially available (trademarked as AROMASIN® by Pfizer, Inc., New York, NY) and was approved by the U.S. Food and Drug Administration (FDA) in 2005. The proposed study may add to a strong research foundation on how steroidal aromatase inhibitors, such as exemestane, impact brain and gonadal gene expression in vertebrates.