Warm temperature promotes sex change in ricefield eel, a protogynous hermaphrodite freshwater fish

The ricefield eel (Monopterus albus) is the only protogynous hermaphrodite freshwater fish. While the mechanism underlying the natural sex change in this species has been fascinating scientists for a long time, it remains elusive and mysterious.

In a new study published in Water Biology and Security, a team of researchers in China reported a temperature-induced sex reversal mechanism in ricefield eel.

“We show that warm temperature induces the expression of male sex determination genes in ovarian tissues, and that temperature-induced up-regulation of male genes depends on Trpv4, a cation channel protein that controls calcium flux into a cell,” shares corresponding author Yuhua Sun.

Previous work has revealed that the sex reversing of ricefield eel is accompanied by changes in levels of sex hormones and the expression of sex determination genes. Also, environmental factors, including temperature, light and pH, can influence the onset of the sex reversal.

The state of DNA methylation is correlated to the expression of sex determination genes during sex reversal of ricefield eel, in line with that the DNA methylome is dynamic and can be impacted by environmental factors. It is generally believed that gene-environmental interaction drive the sex reversal.

“The scenario at play here would be that of environmental cues triggering the change of the epigenetic state of genome, which leads to the transcriptional change of sex determination and endocrine genes, eventually resulting in the sex change of ricefield eel,” says Sun. “While this is interesting and reasonable, it is largely descriptive and lack of support by experimental evidences.”

In fact, some outstanding and fundamental questions have not been answered. For instance, which environmental factor is the most important driver? How are environmental cues captured and sensed, and transduced to the sex determination cascades?

“We show that warm temperature induced the expression of male sex determination genes in ovarian tissues, and that temperature-induced up-regulation of male genes depends on a cation channel thermosensor protein called Trpv4,” explains Sun. 

Trpv4 is a transmembrane protein that belongs to the transient receptor potential ion channel family, which can control the calcium flux into a cell in response to temperature cues. The identification and characterization of Trpv4 is important, as it fills the gap between temperature and the sex determination cascades.

“Our findings offer new insights into the mechanism underlying sex reversal of ricefield eel, which is a refreshing cognition,” adds Sun. “This leads to the potential of sex control breeding of this economically important aquaculture fish, as temperatures can be easily and conveniently controlled in an environmentally friendly manner.”

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Contact the author: Yuhua Sun; the Institute of Hydrobiology, Chinese Academy of Sciences; sunyh@ihb.ac.cn

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