Neuropeptide B in Nile tilapia Oreochromis niloticus: Molecular cloning and its effects on the regulation of food intake and mRNA expression of growth hormone and prolactin

• NPB was mainly expressed in the CNS of Nile tilapia.
• The hypothalamus is the major site for NPB expression in Nile tilapia.
• The hypothalamic NPB may play roles in the regulation of food intake in Nile tilapia.
• NPB could regulate the mRNA expression of GH and PRL in the pituitary of Nile tilapia.

Neuropeptide B (NPB) regulates food intake, energy homeostasis and hormone secretion in mammals via two G-protein coupled receptors, termed as GPR 7 and GPR 8. However, there is no study that reports the function of NPB in teleosts. In this study, the full-length cDNA of prepro-NPB with the size of 663 bp was cloned from the hypothalamus of Nile tilapia. The CDS of the prepro-NPB is 387 bp which encodes a precursor protein with the size of 128 a.a. This precursor contains a mature peptide with the size of 29 a.a, and it was named as NPB29. Tissue distribution study showed that this gene was mainly expressed in different parts of brain, especially in the diencephalon as well as hypothalamus, and the spinal cord in Nile tilapia. Fasting significantly stimulated the mRNA expression of NPB in the brain area without hypothalamus, and refeeding after fasting for 3 and 14 days also showed similar effects on NPB expression. While, only short-term fasting (3 days) and refeeding after fasting for 7 and 14 days induced mRNA expression of NPB in the hypothalamus. Intraperitoneal (i.p.) injection of NPB remarkably elevated the mRNA expression of hypothalamic neuropeptide Y (NPY), cholecystokinin 1 (CCK1) and pituitary prolactin (PRL), whereas significantly inhibited growth hormone (GH) expression in pituitary. These observations in the present study suggested that NPB may participate in the regulation of feeding and gene expression of pituitary GH and PRL in Nile tilapia.