title: The Olfactory Transcriptome and Progression of Sexual Maturation in Homing Chum Salmon Oncorhynchus keta.
abstract: Reproductive homing migration of salmonids requires accurate interaction between the reception of external olfactory cues for navigation to the spawning grounds and the regulation of sexual maturation processes. This study aimed at providing insights into the hypothesized functional link between olfactory sensing of the spawning ground and final sexual maturation. We have therefore assessed the presence and expression levels of olfactory genes by RNA sequencing (RNAseq) of the olfactory rosettes in homing chum salmon Oncorhynchus keta Walbaum from the coastal sea to 75 km upstream the rivers at the pre-spawning ground. The progression of sexual maturation along the brain-pituitary-gonadal axis was assessed through determination of plasma steroid levels by time-resolved fluoroimmunoassays (TR-FIA), pituitary gonadotropin subunit expression and salmon gonadotropin-releasing hormone (sgnrh) expression in the brain by quantitative real-time PCR. RNAseq revealed the expression of 75 known and 27 unknown salmonid olfactory genes of which 13 genes were differentially expressed between fish from the pre-spawning area and from the coastal area, suggesting an important role of these genes in homing. A clear progression towards final maturation was characterised by higher plasma 17α,20β-dihydroxy-4-pregnen-3-one (DHP) levels, increased pituitary luteinizing hormone β subunit (lhβ) expression and sgnrh expression in the post brain, and lower plasma testosterone (T) and 17β-estradiol (E2) levels. Olfactomedins and ependymin are candidates among the differentially expressed genes that may connect olfactory reception to the expression of sgnrh to regulate final maturation.
authors.affiliation: Institute for Marine Resources and Ecosystem Studies (IMARES), Wageningen University and Research Centre, Korringaweg 5, 4401 NT Yerseke, The Netherlands; Animal Breeding and Genomics Centre, Wageningen UR Livestock Research, PO Box 338, 6700 AH Wageningen, The Netherlands.
authors.forename: Arjan P
authors.initials: AP
authors.lastname: Palstra
authors.affiliation: Laboratory of Aquatic Bioresources and Ecosystem, Section of Ecosystem Conservation, Field Science Center for Northern Biosphere, Hokkaido University, Sapporo, 060-0809 Hokkaido, Japan.
authors.forename: Kosuke
authors.initials: K
authors.lastname: Fukaya
authors.affiliation: School of Marine Biosciences, Kitasato University, Kitasato 1-15-1, Minami-ku, Sagamihara, Kanagawa 252-0373, Japan.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Chiba
authors.affiliation: ZF-screens BV, J.H. Oortweg 19, 2333 CH Leiden, The Netherlands.
authors.forename: Ron P
authors.initials: RP
authors.lastname: Dirks
authors.affiliation: Departament de Fisiologia i Immunologia, Facultat de Biologia, Universitat de Barcelona and Institut de Biomedicina de la Universitat de Barcelona (IBUB), Barcelona, Spain.
authors.forename: Josep V
authors.initials: JV
authors.lastname: Planas
authors.affiliation: Laboratory of Aquatic Bioresources and Ecosystem, Section of Ecosystem Conservation, Field Science Center for Northern Biosphere, Hokkaido University, Sapporo, 060-0809 Hokkaido, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Ueda
mesh_terms: D000818:Animals; D005260:Female; D029941:Fish Proteins / Q000235:genetics / Q000378:metabolism; D005640:Follicle Stimulating Hormone / Q000235:genetics / Q000378:metabolism; D007987:Gonadotropin-Releasing Hormone / Q000235:genetics / Q000378:metabolism; D006062:Gonadotropins / Q000235:genetics / Q000378:metabolism; D007986:Luteinizing Hormone / Q000235:genetics / Q000378:metabolism; D008297:Male; D018034:Olfactory Receptor Neurons / Q000378:metabolism; D017685:Oncorhynchus keta / Q000254:growth & development* / Q000378:metabolism; D009928:Organ Specificity; D010902:Pituitary Gland / Q000378:metabolism; D018035:Receptors, Odorant / Q000235:genetics / Q000378:metabolism; D012741:Sexual Maturation; D012903:Smell; D059467:Transcriptome
chemical_list: D029941:Fish Proteins; D006062:Gonadotropins; D018035:Receptors, Odorant; D007987:Gonadotropin-Releasing Hormone; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone