Characterization and expression analysis of gpr173a and gpr173b revealed their involvement in reproductive regulation in spotted scat (Scatophagus argus)

Abstract

Spotted scat (Scatophagus argus) is an economically important mariculture fish worldwide. However, its latent mechanisms of reproductive regulation remain unclear. G protein-coupled receptor 173 (GPR173) is the putative receptor of phoenixin (Pnx), which together play a role in reproductive regulation. However, little is known about the function of gpr173 in S. argus. Herein, two gpr173 genes in S. argus are identified: gpr173a and gpr173b. Tissue distribution suggested that both gpr173a and gpr173b were highly expressed in the hypothalamus and pituitary gland in both male and female S. argus. During ovarian development, the expression of hypothalamic gpr173a was highest in phase V. Meanwhile, the expression of hypothalamic gpr173b was most pronounced in phases II and V. In the pituitary gland of female S. argus, the expressions of gpr173a and gpr173b were the highest in phase III. During testicular development, the expressions of hypothalamic gpr173a and gpr173b were highest in phase V, and the expressions of pituitary gpr173a and gpr173b in phase IV and V were considerably higher than in phase III. After injection with 4 mg·kg–1 17β-estradiol (E2), the expression of hypothalamic gpr173a decreased. Meanwhile, the expression of hypothalamic gpr173b increased significantly. However, when hypothalamus cells were cultured in vitro with E2 (10 μM) for 12 h, the expression of both gpr173a and gpr173b increased significantly. Additionally, in cultured hypothalamus cells, EPA increased the expression of gpr173b but decreased the gpr173a expression. Meanwhile DHA increased gpr173b expression but did not affect gpr173a mRNA levels. This study is the first to characterise gpr173a and gpr173b in S. argus, providing important data concerning the function of gpr173a and gpr173b in the reproductive modulation of S. argus.