Search for genes involved in the temperature-induced gonadal sex differentiation in the tilapia, Oreochromis niloticus

In the tilapia, Oreochromis niloticus, sex is determined by genetic factors (XX/XY) but temperature can also influence the gonadal sex differentiation . Elevated temperatures of 35 degreesC can generate functional male phenoty pes if applied before and during sexual differentiation. The genes and mech anisms by which temperature acts on the cascade leading to sex differentiat ion have been investigated. Two strategies have been followed: 1) Search fo r novel genes by differential display, and 2) Expression studies of candida te genes. Genetically all-female and all-male progenies were reared at 27 d egreesC (natural temperature) and at 35 degreesC (masculinizing treatment) and gonads dissected. Using differential display, we isolated a 300 bp cDNA (MM20C) from temperature-masculinized females. Virtual northern analysis r evealed a 1.2 kb transcript in 35 degreesC treated females and males, but h ardly any expression in natural females (27 degreesC). Semi-quantitative RT -PCR established a several-fold increase in MM20C expression in 35 degreesC masculinized fry. Elevated expression was observed in natural males (27 de greesC) with higher levels detected in those reared at 35 degreesC. Further more, we have analyzed as a candidate gene the P450 11 beta -hydroxylase, a n important androgen steroidogenic enzyme. Low levels of expression were fo und in natural males. This coincides with low concentrations of 11 ketotest osterone in the gonads before and during gonadal sex differentiation. Highe r expression levels of 11 beta -hydroxylase were detected in male gonads at 35 degreesC but levels in phenotypic males were similar to those found for natural females. Previous results reported that expression of aromatase is repressed by masculinizing treatments. Our study demonstrated that masculi nizing-temperature can also stimulate the expression of other gene(s). J. E xp. Zool. 290:574-585, 2001. (C) 2001 Wiley-Liss, Inc.