Phoenixin participated in regulation of food intake and growth in spotted scat, Scatophagus argus

Phoenixin (Pnx) is an endogenous peptide known to be involved in reproduction and food intake in rats, with two active isoforms, phoenixin-14 (Pnx-14) and phoenixin-20 (Pnx-20). However, little is known about the functions of Pnx in teleost. Here, pnx was cloned and was detected in all tissues of both male and female in spotted scat (Scatophagus argus), including growth axis, hypothalamus, pituitary, and liver. Real-time PCR analysis showed that pnx in the hypothalamus increased significantly after 2 d and 7 d fasting, while reduced significantly after re-feeding (P < 0.05). When pituitary and liver fragments were cultured in vitro with Pnx-14 and Pnx-20 (10 nM and 100 nM) for 6 h, the expression of ghrh1 (growth hormone-releasing hormone receptor) and gh (growth hormone) in the pituitary, and ghrl (growth hormone receptor 1) in the liver increased significantly, except ghr2 (growth hormone receptor 2) incubated with 10 nM and 100 nM Pnx-20 and ghrl incubated with 10 nM Pnx-20. Similarly, the expression of ghrhr and gh in the pituitary, as well as ghrl and ghr2 in the liver, increased significantly after injecting S. argus with Pnx-14 and Pnx-20 (10 ng/g and 100 ng/g body weight). These results indicate that Pnx is likely to be involved in the regulation of food intake, and also regulates the growth of S. argus by increasing ghrhr and gh expression in the pituitary, ghrl and ghr2 in the liver, and ghrl directly in the liver.