Abstract
Phoenixin-20 (PNX-20) is a bioactive peptide with hormone-like actions in vertebrates. In mammals, PNX stimulates hypothalamo-pituitary-gonadal hormones and regulate reproductive processes. Our immunohisto/cytochemical studies show PNX-like and the putative PNX receptor, SREB3-like immunoreactivity in the gonads of zebrafish, and in zebrafish liver (ZFL) cells. Intraperitoneal injection of zebrafish PNX-20 upregulates mRNAs encoding both salmon gonadotropin-releasing hormone (GnRH), and chicken GnRH-II and kisspeptin and its receptor in zebrafish hypothalamus. Similarly, luteinizing hormone receptor mRNA expression in the testis, follicle-stimulating hormone receptor in the ovary, and the kisspeptin system were upregulated in the gonads of PNX-20 injected fish. We also observed the upregulation of genes involved in the sex steroidogenic pathway (cyp11a1, cyp17a1, 17βhsd, cyp19a1a) in the gonads of PNX-20 administered fish. PNX-20 upregulates the expression of vitellogenin isoforms and estrogen receptor (esr2a and 2b) mRNAs in ZFL cells in vitro. Meanwhile, siRNA-mediated knockdown of PNX-20 resulted in the downregulation of all vitellogenin transcripts, further suggesting its possible role in vitellogenesis. PNX-20 treatment resulted in a significant increase in germinal vesicle breakdown in zebrafish follicles in vitro. Collectively, these results provide strong evidence for PNX-20 effects on the HPG axis and liver to promote reproduction in zebrafish.
Highlights
Laboratory of Integrative Neuroendocrinology, Department of Veterinary Biomedical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, S7N 5B4, Saskatchewan, Canada. *email: suraj.unniappan@ usask.ca www.nature.com/scientificreports/
Our research determined the effects of PNX-20 on all three tissues in the HPG axis, and liver, a major source of vitellogenin that is critical for ovarian follicle biology
The local expression suggests a possible role of PNX-20 in zebrafish reproduction
Summary
It was reported that both in vitro and in vivo administration of PNX upregulates the expression of gnrh receptor (gnrhr), lh and fsh in the pituitary of spotted scat[12]. These results suggest PNX appears to have a regulatory role in reproduction in fish. This research aimed to determine whether PNX-20 has a reproductive regulatory role in zebrafish, a well-characterized model system in comparative endocrinology. We tested for possible effects of PNX-20 on the tissue-specific expression of mRNAs encoding reproductive regulatory peptides, and vitellogenin genes in the liver, and oocyte maturation in zebrafish. Our results indicate that PNX-20 is a positive modulator of the HPG axis and vitellogenesis, and promotes oocyte maturation in zebrafish
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