title: Variation in branchial expression among insulin-like growth-factor binding proteins (igfbps) during Atlantic salmon smoltification and seawater exposure.
abstract: BACKGROUND
  In preparation for migration from freshwater to marine habitats, Atlantic salmon (Salmo salar L.) undergo smoltification, a transformation that includes the acquisition of hyposmoregulatory capacity. The growth hormone (Gh)/insulin-like growth-factor (Igf) axis promotes the development of branchial ionoregulatory functions that underlie ion secretion. Igfs interact with a suite of Igf binding proteins (Igfbps) that modulate hormone activity. In Atlantic salmon smolts, igfbp4,-5a,-5b1,-5b2,-6b1 and-6b2 transcripts are highly expressed in gill. We measured mRNA levels of branchial and hepatic igfbps during smoltification (March, April, and May), desmoltification (July) and following seawater (SW) exposure in March and May. We also characterized parallel changes in a broad suite of osmoregulatory (branchial Na+/K+-ATPase (Nka) activity, Na+/K+/2Cl-cotransporter 1 (nkcc1) and cystic fibrosis transmembrane regulator 1 (cftr1) transcription) and endocrine (plasma Gh and Igf1) parameters.
  
  
  RESULTS
  Indicative of smoltification, we observed increased branchial Nka activity, nkcc1 and cftr1 transcription in May. Branchial igfbp6b1 and -6b2 expression increased coincidentally with smoltification. Following a SW challenge in March, igfbp6b1 showed increased expression while igfbp6b2 exhibited diminished expression. igfbp5a,-5b1 and-5b2 mRNA levels did not change during smolting, but each had lower levels following a SW exposure in March.
  
  
  CONCLUSIONS
  Salmonids express an especially large suite of igfbps. Our data suggest that dynamic expression of particular igfbps accompanies smoltification and SW challenges; thus, transcriptional control of igfbps may provide a mechanism for the local modulation of Igf activity in salmon gill.
authors.affiliation: Department of Biology, Skidmore College, 815 N Broadway, Saratoga Springs, 12866, NY, USA. jbreves@skidmore.edu.
authors.forename: Jason P
authors.initials: JP
authors.lastname: Breves
authors.affiliation: Department of Biology, Skidmore College, 815 N Broadway, Saratoga Springs, 12866, NY, USA.
authors.forename: Chelsea K
authors.initials: CK
authors.lastname: Fujimoto
authors.affiliation: Department of Biology, Skidmore College, 815 N Broadway, Saratoga Springs, 12866, NY, USA.
authors.forename: Silas K
authors.initials: SK
authors.lastname: Phipps-Costin
authors.affiliation: Fish Endocrinology Laboratory, Department of Biological and Environmental Sciences, University of Gothenburg, Box 463, SE-40530, Gothenburg, Sweden.
authors.forename: Ingibjörg E
authors.initials: IE
authors.lastname: Einarsdottir
authors.affiliation: Fish Endocrinology Laboratory, Department of Biological and Environmental Sciences, University of Gothenburg, Box 463, SE-40530, Gothenburg, Sweden.
authors.forename: Björn Thrandur
authors.initials: BT
authors.lastname: Björnsson
authors.affiliation: USGS, Leetown Science Center, S.O. Conte Anadromous Fish Research Center, P.O. Box 796, One Migratory Way, Turners Falls, 01376, MA, USA.
authors.forename: Stephen D
authors.initials: SD
authors.lastname: McCormick
mesh_terms: D000064:Acclimatization / Q000502:physiology*; D000818:Animals; D017753:Ecosystem; D005618:Fresh Water; D005880:Gills / Q000378:metabolism*; D018969:Insulin-Like Growth Factor Binding Proteins / Q000096:biosynthesis* / Q000097:blood; D064587:Osmoregulation / Q000502:physiology; D020317:Salmo salar / Q000097:blood / Q000378:metabolism*; D012623:Seawater
chemical_list: D018969:Insulin-Like Growth Factor Binding Proteins
keywords: Atlantic salmon; Binding proteins; Gill; Growth hormone; Insulin-like growth-factor; Liver; Osmoregulation; Salinity; Smoltification