Gender-specific expression of multiple estrogen receptors, growth hormone receptors, insulin-like growth factors and vitellogenins, and effects of 17β-estradiol in the male tilapia (Oreochromis mossambicus)

Gender-specific expression of estrogen receptors (ERα and ERβ), growth hormone receptors (GHR1 and GHR2), insulin-like growth factors (IGF-I and IGF-II) and three vitellogenins (Vgs A–C) was examined in the liver, gonad, pituitary, and brain of sexually mature male, female, and 17β-estradiol (E2)-treated male tilapia (Oreochromis mossambicus). Reflecting greater growth rate in male tilapia, hepatic expression of GHR1, GHR2, IGF-I and IGF-II as well as plasma IGF-I levels were higher in males than in females, whereas the expression of Vgs A–C and ERα was higher in females. On the other hand, expression of all genes measured was higher in the ovary than in testis. Forty eight hours after E2 injection (5 μg/g) into male fish, hepatic expression of most transcripts measured were altered to levels that were similar to those seen in females. The changes included decreased expression of GHR1, GHR2, IGF-I, and IGF-II, and increased expression of ERα and Vgs A–C. E2 treatment also increased Vg and decreased IGF-I in the plasma. Brain expression of ERα, ERβ, GHR1, and IGF-I was higher in females than in males, whereas pituitary expression of GHR2 and IGF-I was lower in females; only brain expression of GHR1 was increased by E2 treatment. These findings suggest that E2 stimulates Vg production primarily through activation of ERα and down-regulation of the GH/IGF-I axis, thus shifting energy from somatic growth towards vitellogenesis at the level of the liver.