|Molecular biological studies on kisspeptin during gonadal maturation in salmon|
Monty, M. (2011). Molecular biological studies on kisspeptin during gonadal maturation in salmon. MSc Thesis. Hokkaido University: Hokkaido. 27, V pp.
Oncorhynchus keta (Walbaum, 1792) [WoRMS]; Oncorhynchus nerka (Walbaum, 1792) [WoRMS]; Marien
kisspeptin; kiss1; kiss2; puberty; Oncorhynchus nerka; Oncorhynchus keta
Since salmon have amazing abilities to migrate long distances from the ocean to their natal streams for spawning, endocrinological controlling mechanisms in the hypothalamus-pituitary-gonadal (BPG) axis have crucial roles in successful homing migration that is closely related to gonadal maturation, via GnRH pathways. Controlling mechanisms in sGnRH activity in the salmon brain remains unclear. Kisspeptin, which has been identified by the product of the gene Kiss1, is a G-protein coupled receptor ligand for kisspeptin receptor (formerly called GPR54). It has recently become clear that kisspeptin-receptor signaling has an important role in initiating GnRH secretion at puberty in mammals. In this study, we isolated and characterized sockeye salmon and chum salmon Kiss2 sequence. Degenerated primers are used for the PCR amplifications, to isolate partial-length fragments from sockeye salmon and chum salmon brain mRNA. To identify patterns of expression among tissues, gene-specific primers and ß-actin primer were used to amplify with PCR cDNA from lacustrine sockeye salmon olfactory epithelium, brain (olfactory bulb, telencephalon, hypothalamus, optic tectum, cerebellum and medulla oblongata), pituitary gland, kidney, liver, retina, heart, intestine, muscle, gill and gonads (ovary and testis). The same specific primers were used to show the age-related expression of kiss2 in sockeye salmon. In order to evaluate the expression pattern of Kiss2 during homing migration, semi--quantitative PCR were carried out on chum salmon brain samples. Supposing the distance in the river to the spawning area would reflect the level of gonadal maturation of fish, individuals were samples in three different locations along their native river. We could identify partial-length kiss2 cDNA sequences in both salmon species. Sockeye salmon Kiss2 appeared to be widely expressed in neural and peripheral tissues. The expression in the brain started for the first year of life. We did not identify a variation of chum salmon kiss2 expression during homing migration. We were not able to isolate kiss1 neither in chum salmon nor in sockeye salmon