Pituitary adenylate cyclase-activating polypeptide related peptide (PRP) in an Anabantidae fish: its mRNA expression in the brain during gonadal development and sexual behavior and its hypophysiotropic effect on pituitary hormonal gene expression
Gal Levy1,2, Yoav Gothilf1 & Gad Degani2,3
Pituitary adenylate cyclase activating polypeptide - related peptide (PRP) (formerly known as growth hormone releasing hormone-like peptide GHRHLP) can act as a hypophysiotropic factor in several teleosts by stimulating growth hormone (GH) secretion. However, as yet, no information on this peptide as a regulator of reproduction exists. Recently, the full-length PRP cDNA was cloned in the blue gourami (Trichogaster trichopterus) and was found to be expressed in the brain. Thus, the aims of the present study were to investigate the PRP gene expression pattern during sexual behavior and oogenesis, as well as to learn its effect on pituitary hormonal transcription in a primary culture of dispersed pituitary cells using the quantitative real-time PCR method. Our results demonstrated that the blue gourami PRP (bgPRP) mRNA levels were higher in mature non-reproductively active males than in nest builders and juveniles. In addition, higher mRNA levels were detected in females with oocytes in the final maturation stage, as compared to in vitellogenic individuals. Stimulation of pituitary cells with bgPRP increased βLH and βLH subunit levels only in females, whereas in males only GH mRNA levels rose upon bgPRP stimulation. Based on these results, we propose that in the blue gourami, bgPRP, as a hypophysiotropic factor, may act differentially on the gonadotropic axes in females and males, up-regulating their gonadotropin and GH mRNA levels, respectively. This research provides a basis for the further understanding of the integrative network that regulates growth and reproduction. Such knowledge may contribute to hormonal treatments and manipulations in aquaculture.