Steroid enzyme gene expressions during natural and androgen‐induced gonadal differentiation in the rainbow trout, Oncorhynchus mykiss

Abstract

In fish, according to Yamamoto's model, androgens would drive testis differentiation and estrogens ovarian differentiation. In order to study the implication of steroid enzymes in rainbow trout gonadal differentiation, we examined the expression of some steroid enzyme genes during natural differentiation (cholesterol side chain cleavage = P450scc, 17-hydroxylase/lyase = P450c17, 3beta-hydroxysteroid dehydrogenase = 3betaHSD) and androgen-induced differentiation (P450scc, P450c17, 3betaHSD, aromatase = P450aro, and 11beta-hydroxylase = P45011beta). Expressions of P450scc, 3betaHSD, and P450c17 were all detected in male and female gonads at 55 days post-fertilization (dpf), i.e., two weeks before histological differentiation. There were no differences in their expression level respective to the sex. The androgen treatment was carried out by administration of 11beta-hydroxyandrostenedione (11betaOHDelta4) in genetic all-female populations and the resulting sex ratios were found to be 100% male even at a low dosage of 1 mg/kg of food. Following 11betaOHDelta4 treatment, only the expression of P450c17 was found to be sustained when compared with the female untreated control. In contrast, P450scc was clearly up-regulated and 3betaHSD and P450aro down-regulated by the androgen treatment. P45011beta gene expression remained low in gonads of androgen-treated females, as it did in control untreated females. These results together demonstrate that steroidogenesis in rainbow trout is potentially active in pre-differentiating gonads of both sexes, and that one of the masculinizing actions of androgens in the species may be to down-regulate the female-specific gonadal P450aro gene expression. However, in vivo androgen treatment in genetic females does not induce the same pattern of steroid gene expression as in genetic males. These data suggest that exogenous androgens might induce a male differentiation process with P450aro inhibition being one of the steps required. However, this process would not involve endogenously produced 11-oxygenated androgens.

An evolutionary and functional analysis of FoxL2 in rainbow trout gonad differentiation

“…The masculinizing effects of androgens are probably triggered by the suppression of estrogen synthesis through inhibition of aromatase gene expression. The inhibition of aromatase following androgen treatment in females has already been reported in rainbow trout (Govoroun et al 2001b). Here we have shown that an aromatase inhibitor can also induce a similar expression profile.…”

“…Total RNA was isolated using TRIzol reagent (Invitrogen) as previously described (Govoroun et al 2001b). Total RNA concentration was determined with an Agilent 2100 Bioanalyzer and the RNA 6000 LabChip kit (Agilent Technologies, Colorado Springs, CO, USA) according to the manufacturer's instructions.…”

“…However, successful development of the gonads may be influenced by exposure to exogenous steroids during a critical period of gonadal differentiation. This may lead to reversal of the expected phenotypic sex, with the resulting population being fertile (Guiguen et al 1999, Govoroun et al 2001b). In our context, following EE2 treatment of males leading to an effective feminization (Fig.…”

Characterization of early molecular sex differentiation in rainbow trout, Oncorhynchus mykiss

“…This late steroidogenic potential is probably the reflection of a late differentiation and/or proliferation of the Leydig cell lineage, as we only detected very few positive cells for cyp17a1, cyp11a1, and cyp11b2.1 during this period of testicular differentiation. The previous studies carried out on trout were started at a late undifferentiated period (by 55 dpf) when steroid enzymes related to androgen synthesis displays a clear dimorphic expression in males (Liu et al, 2000;Govoroun et al, 2001). The present work confirms that steroid and androgen synthesis enzymes are up-regulated in male gonads but only after 45-55 dpf.…”

“…Despite the fact that androgenic treatments are able to induce a complete functionally phenotypic masculinisation of genetically all female populations (Liu et al, 2000;Devlin and Nagahama, 2002), the potential for androgen synthesis could not always be detected before testicular differentiation in teleost fish (Nakamura et al, 2003). For instance, in the Nile tilapia it has been suggested that androgen synthesis is absent during this process (Nakamura et al, 1998;Nakamura et al, 2003) whereas, in rainbow trout, some studies support the idea that endogenous androgens could drive testicular differentiation (Liu et al, 2000;Govoroun et al, 2001). However in rainbow trout these studies were carried out before the first sign of morphological go-nadal differentiation, and the expression of some genes was already sexually dimorphic at the earliest sampling point investigated, such as aromatase (cyp19a1) in females and 11␤-hydroxylase (cyp11b2.1) in males.…”