Abstract
BackgroundControlling and managing the breeding of bluefin tuna (Thunnus spp.) in captivity is an imperative step towards obtaining a sustainable supply of these fish in aquaculture production systems. Germ cell transplantation (GCT) is an innovative technology for the production of inter-species surrogates, by transplanting undifferentiated germ cells derived from a donor species into larvae of a host species. The transplanted surrogates will then grow and mature to produce donor-derived seed, thus providing a simpler alternative to maintaining large-bodied broodstock such as the bluefin tuna. Implementation of GCT for new species requires the development of molecular tools to follow the fate of the transplanted germ cells. These tools are based on key reproductive and germ cell-specific genes. RNA-Sequencing (RNA-Seq) provides a rapid, cost-effective method for high throughput gene identification in non-model species. This study utilized RNA-Seq to identify key genes expressed in the gonads of Southern bluefin tuna (Thunnus maccoyii, SBT) and their specific expression patterns in male and female gonad cells.ResultsKey genes involved in the reproductive molecular pathway and specifically, germ cell development in gonads, were identified using analysis of RNA-Seq transcriptomes of male and female SBT gonad cells. Expression profiles of transcripts from ovary and testis cells were compared, as well as testis germ cell-enriched fraction prepared with Percoll gradient, as used in GCT studies. Ovary cells demonstrated over-expression of genes related to stem cell maintenance, while in testis cells, transcripts encoding for reproduction-associated receptors, sex steroids and hormone synthesis and signaling genes were over-expressed. Within the testis cells, the Percoll-enriched fraction showed over-expression of genes that are related to post-meiosis germ cell populations.ConclusionsGonad development and germ cell related genes were identified from SBT gonads and their expression patterns in ovary and testis cells were determined. These expression patterns correlate with the reproductive developmental stage of the sampled fish. The majority of the genes described in this study were sequenced for the first time in T. maccoyii. The wealth of SBT gonadal and germ cell-related gene sequences made publicly available by this study provides an extensive resource for further GCT and reproductive molecular biology studies of this commercially valuable fish.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-2397-8) contains supplementary material, which is available to authorized users.
Highlights
Bluefin tunas (Thunnus spp.) provide some of the highest valued fish in the fresh and frozen international fish market and as such, they are highly susceptible to overfishing, resulting in strict fishing regulations and quotas, which limit the available catch [1]
Bluefin tuna broodstock must be bred in captivity and extensive research has been invested into facilitating the reproduction in captivity and broodstock management of three major bluefin tuna species: Pacific bluefin tuna (PBT, Thunnus orientalis), Atlantic bluefin tuna (BFT, Thunnus thynnus thynnus) and Southern bluefin tuna (SBT, Thunnus maccoyii)
Southern bluefin tuna gonad samples Twelve SBT were sampled on May 27, 2014 from Cleanseas Tuna Ltd. sea-pens located in Port Lincoln bay, South Australia
Summary
Bluefin tunas (Thunnus spp.) provide some of the highest valued fish in the fresh and frozen international fish market and as such, they are highly susceptible to overfishing, resulting in strict fishing regulations and quotas, which limit the available catch [1]. Molecular techniques and tools are becoming increasingly helpful to identify key pathways and biological processes involved in bluefin tunas reproductive biology Such molecular research includes the discovery of the Kisspeptin system in SBT [3], treatment of gonadotropin releasing hormone agonist (Gnrha) to induce spawning in BFT and SBT [4, 5], description of gene expression patterns in gonads of BFT [6, 7] and identification of germ cell specific molecular markers in PBT [8]. This study utilized RNA-Seq to identify key genes expressed in the gonads of Southern bluefin tuna (Thunnus maccoyii, SBT) and their specific expression patterns in male and female gonad cells
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