Sexually dimorphic expression of pituitary glycoprotein hormones in a sex-changing fish (Pseudolabrus sieboldi)

It is widely accepted that the hypothalamic-pituitary-gonadal axis is involved in gonadal sex change in socially controlled sex-changing fish. However, the specific secretion profiles of pituitary gonadotropins (GtHs) in this type of fish are not known. To address this fundamental question, we demonstrated that the diurnal secretion patterns of GtHs differ distinctly between males and females in a socially controlled sex-changing fish. We analyzed the pituitary mRNA levels of glycoprotein hormone subunits (i.e., the common α-subunit and specific β-subunits follicle-stimulating hormone β, luteinizing hormone β, and thyroid-stimulating hormone β) in the wrasse Pseudolabrus sieboldi, which is a model fish that exhibits accurate diurnal rhythms of gametogenesis in both males and females. Northern blots clearly showed that each subunit gene exhibits a diurnal rhythm of expression in the pituitary and that the expression patterns differ distinctly between the sexes. Our results suggest that oogenesis and spermatogenesis in this hermaphroditic fish are regulated differentially through the distinct secretion patterns of pituitary glycoprotein hormones. This study also provides direct evidence of the sexual plasticity of pituitary GtH secretion in a socially controlled sex-changing fish.