Impact of low temperature during embryonic development on the sex determination and de novo DNA methyltransferases in the androdiecious fish Kryptolebias marmoratus

The teleost fish Kryptolebias marmoratu (mangrove rivulus) presents an unusual reproductive system as it is one of only two vertebrates in which hermaphroditic individuals can reproduce by self-fertilization but also outcross with males. Between different populations of rivulus, sex ratios are variable as sex determination processes are based on genetic and environmental factors. In laboratory, isogenic lineages that avoid genetic diversity can be produced, allowing to study the effect of environment only. Even though low temperature is known to impact the sex ratio by inducing male development, and epigenetic mechanisms are suspected to make the connection between environment and sexual gene expression, most of the mechanisms behind sex determination of K. marmoratus by temperature are still unknown. To better understand these processes, we compared the expression level of the de novo DNA methyltransferases dnmt3aa and dnmt3ab as well as those of the sexual genes sox9a and cyp19b in rivulus embryos incubated at 18°C and 25°C. Even though we could not show a correlation between dnmt3a and sexual genes expression, we found that, while dnmt3aa and dnmt3ab are similarly expressed for a same temperature, the level expression of both dnmt3a variants seems to increase at a faster rate at 18°C compared to 25°C, at least during the early stages of embryonic development. In parallel, we observed that in the last stages of embryonic development, sox9a was overexpressed at 18°C while cyp19b was overexpressed as 25°C. This study may be a starting point for further research to prove a correlation, or even a causality, between de novo methyltransferases and sexual genes as a pathway to explain temperature-dependent sex determination in mangrove rivulus.