Abstract
Our aim was to study the relationship between the sex-determining genes, sox9a and cyp19a, and water temperature in Gadus chalcogrammus. We assessed the sex ratio based on the expression levels of sox9a and cyp19a at different water temperatures (5, 8, 11, and 14 °C) and at different stages of walleye pollock development (embryos, larvae, and juveniles). Next, we used immature walleye pollock to assess sox9a expression in males and cyp19a and vitellogenin (VTG) expression in females at different water temperatures. Males expressed sox9a in the gonadal tissues, while females expressed cyp19a in the gonadal tissues and VTG in the blood plasma. In the first experiment, cyp19a expression was higher at 5 °C and 8 °C, and sox9a expression was higher at 11 and 14 °C. In the second experiment, sox9a expression remained relatively stable, but cyp19a expression decreased with increasing temperature, decreasing significantly after 14 °C. Similar patterns were also observed for VTG expression. These results indicate that lower water temperatures increase cyp19a expression, which increases the female ratio. Higher water temperatures increase sox9a expression, which increases the male ratio. Therefore, this study highlights the potential of the sex-determining genes and the influence of water temperature.
Highlights
Walleye pollock (Gadus chalcogrammus) resides in the coastal waters of Korea and Japan, throughout the Kamchatka Peninsula and the Bering Sea and into the central coast areas of California [1]
Sex determination happens at an early developmental stage, and sex is determined by a combination of genetic-dependent sex determination (GSD), environment-dependent sex determination (ESD) such as temperature, density, pH, and hypoxia, and endocrine factors [12,13,14]
Sox9a was only found in male gonadal tissues while cyp19a was only found in female gonadal tissues (Figure 2B)
Summary
Walleye pollock (Gadus chalcogrammus) resides in the coastal waters of Korea and Japan, throughout the Kamchatka Peninsula and the Bering Sea and into the central coast areas of California [1]. Water temperature influences habitat selection, migration, and physiological changes in walleye pollock, including sex determination, reproduction, growth, hormonal changes, and metabolism [4,5,6,7,8,9]. Environmental factors such as the water temperature are important to sex determination [10,11]. Sexual differentiation is achieved by a positive feedback loop of cytochrome P450 aromatase (cyp19a), which involves the transcription factor forkhead box protein L2 (foxl2) [21,22]. Cyp19a is used for steroidogenesis of the gonadal steroids, which plays a critical role in gonadogenesis
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