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Abstract
Background: Nowadays, the molecular mechanisms governing TSD (temperature-dependent sex determination) or GSD + TE (genotypic sex determination + temperature effects) remain a mystery in fish. Methods: We developed three all-female families of Nile tilapia (Oreochromis niloticus), and the family with the highest male ratio after high-temperature treatment was used for transcriptome analysis. Results: First, gonadal histology analysis indicated that the histological morphology of control females (CF) was not significantly different from that of high-temperature-treated females (TF) at various development stages. However, the high-temperature treatment caused a lag of spermatogenesis in high-temperature-induced neomales (IM). Next, we sequenced the transcriptome of CF, TF, and IM Nile tilapia. 79, 11,117, and 11,000 differentially expressed genes (DEGs) were detected in the CF–TF, CF–IM, and TF–IM comparisons, respectively, and 44 DEGs showed identical expression changes in the CF–TF and CF–IM comparisons. Principal component analysis (PCA) indicated that three individuals in CF and three individuals in TF formed a cluster, and three individuals in IM formed a distinct cluster, which confirmed that the gonad transcriptome profile of TF was similar to that of CF and different from that of IM. Finally, six sex-related genes were validated by qRT-PCR. Conclusions: This study identifies a number of genes that may be involved in GSD + TE, which will be useful for investigating the molecular mechanisms of TSD or GSD + TE in fish.
Highlights
Nile tilapia (Oreochromis niloticus) are the third most important aquaculture fish after carp and salmon, and males grow significantly faster than females
These results further verified the existence of a clear genotype-by-environment (GxE) interaction during the sex determination and differentiation processes in Nile tilapia
In the control females (CF)–induced neomales (IM) comparison, we found 11,117 differentially expressed genes (DEGs), and Principal component analysis (PCA) indicated that three individuals in CF and three individuals in IM formed a distinct cluster on the PCA plot (Figure 4)
Summary
Nile tilapia (Oreochromis niloticus) are the third most important aquaculture fish after carp and salmon, and males grow significantly faster than females. A considerable amount of previous research has centered on the sex determination mechanism and all-male production in Nile tilapia, making this species an ideal one for studying molecular signaling cascades and gene expression networks during sex determination and differentiation [1,3]. There are sex chromosomes in many fish, artificially high or low temperatures during critical thermosensitive periods (TSP) result in their sex ratio changes. These fish are classified as GSD + TE. Methods: We developed three all-female families of Nile tilapia (Oreochromis niloticus), and the family with the highest male ratio after high-temperature treatment was used for transcriptome analysis. Conclusions: This study identifies a number of genes that may be involved in GSD + TE, which will be useful for investigating the molecular mechanisms of TSD or GSD + TE in fish
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