The Role of Secretogranin-IIa and Its Derived Peptide Secretoneurin a in Feeding Regulation in Female Goldfish

Abstract

Secretoneurin (SN) is a 31-43 amino acid, functional peptide derived by proteolytic processing from the middle domain of the ~600 amino acid secretogranin-II (SgII) precursor. In teleosts there are 2 forms arising from 2 different genes, SgIIa and SgIIb. In turn, there are both SNa and SNb in teleost. Secretoneurin is a well-conserved peptide during evolution from fish to mammals and widely distributed in secretory granules of endocrine cells and neurons. Secretoneurin plays important roles in different biological processes, for example controlling vertebrate reproduction by stimulating luteinizing hormone release from the pituitary. A potential new role of SN in feeding in goldfish is the subject of the research presented in this thesis. Firstly, we looked at the distribution of SgIIa mRNA in various female goldfish tissues using both RT-PCR and Q-PCR techniques in order to determine which tissue expresses SgIIa mRNA and in which level. We found that SgIIa mRNA was detected in different amounts in all tissues examined. The main tissues of interest were hypothalamus, telencephalon and gut, they all expressed SgIIa. Secondly, we examined the effect of acute (26 h), short (3 days), medium (7 days) and long (14 days) fasting and periprandial changes on SgIIa mRNA level in hypothalamus, telencephalon and gut using Q-PCR method. The results showed that SgIIa mRNA increases under the effect of acute and short fasting, however, medium and long fasting did not affect SgIIa mRNA. Thirdly, we examined the effect of brain injection of goldfish SNa on food intake and locomotor behavior and the expression of some feeding neuropeptides such as neuropeptide Y, orexin, chocystokinin and cocaine-and amphetamine-regulated transcript I after treatment. Injection of SNa in the third brain ventricle increased food intake and fish activity. Associated with this was an increase in NPY and decrease in CARTI mRNA levels in hypothalamus. The increase in SgIIa mRNA following fasting and the increase of food intake as a result of SNa treatment suggest a novel role for SNa in feeding processes.