An inducible nuclearized splicing variant of kdm6bb mediates high temperature-induced masculinization in Nile tilapia

Hampered by the challenge of discerning the primary molecular events of temperature-dependent sex reversal (TSR) from the secondary effects of sexual differentiation, the players and the underlying mechanisms that translate temperature into a sex-determining signal in fish remains elusive.We conducted combined transcriptomics and genome-wide histone methylation analysis on a serial of early sex determination periods in Nile tilapia gonads exposed to elevated temperature. We uncovered high temperature induced alterations in the H3K27 and H3K4 methylomes that well correlated with the pronounced upregulation of male-promoting genes (amh, dmrt1, gsdf) and the suppression of the female-promoting genes (wt1a, wt1b, fsta). We verified the H3K27 demethylase, kdm6bb, is a primary player contributes significantly to the reduced H3K27 methylation of the male-determining genes, which leads to temperature induced sex reversal. The TSR function of kdm6bb was found to be achieved by alternative inclusion of a previously unreported intron (I8), that exclusively enables nuclear translocation of the demethylase variant, correcting a translation efficiency-based explanation of kdm6bb functioning previously proposed. This study highlighted the critical role of alternative splicing and nuclear-localization of the epigenetic modifiers in temperature induced masculinization in fish.