Cloning of Atlantic halibut growth hormone receptor genes and quantitative gene expression during metamorphosis.
To gain insight into the possible regulatory role of the growth hormone (GH)-insulin-like growth factor I (IGF-I) system in flatfish metamorphosis, body GHR gene expression as well as IGF-I protein content was quantified in larval Atlantic halibut throughout metamorphosis (developmental stages 5-10). The cDNA of the full-length GH receptor (hhGHR) was cloned from adult liver and characterized. The hhGHR shows common features of a GHR, including a (Y/F)GEFS motif in the extracellular domain, a single transmembrane region, and an intracellular domain containing a Box 1 and Box 2. Additionally, a truncated GHR (hhGHRtr), similar to turbot and Japanese flounder GHRtr, was cloned and sequenced. These sequences are highly similar to the full-length and truncated GHRs in turbot (89%/86%) and Japanese flounder (93%/91%) with lower identity with other fish type I GHR (81%) and type II GHRs (58%). A quantitative real-time RT-PCR assay was used to measure hhGHR and hhGHRtr mRNA content in normally and abnormally metamorphosed individuals at six developmental stages, from early pre-metamorphosis to post-metamorphosis, when the fish is considered a juvenile. The level of hhGHR gene expression was highest at pre-metamorphic stage 6 and at stage 8 at the onset of metamorphosis, and then decreased during metamorphic climax and post-metamorphosis. Expression of hhGHRtr reached highest levels at stage 6 and then decreased to post-metamorphosis. The ratio of expression between the full-length and the truncated GHR (hhGHR:hhGHRtr) varied among stages and was highest at the onset of metamorphosis and at metamorphic climax. A radioimmunoassay was used to measure halibut IGF-I body content throughout metamorphosis. IGF-I increases from early metamorphosis to the onset of metamorphosis and then decreases towards post-metamorphosis. In comparison between normally and abnormally metamorphosing larvae, IGF-I content, hhGHR and hhGHRtr mRNA levels were reduced in the abnormal fish. These data indicate that the GH-IGF-I system either has a regulatory role in metamorphosis, or is being affected as a consequence of the abnormal metamorphosis.
Hildahl
Jon
J
Fish Endocrinology Laboratory, Department of Zoology/Zoophysiology, Göteborg University, Box 436, S-40530 Göteborg, Sweden. jon.hildahl@zool.gu.se
Sweeney
Glen
G
Galay-Burgos
Malyka
M
Einarsdóttir
Ingibjörg Eir
IE
Björnsson
Björn Thrandur
BT
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D005432:Flounder / Q000235:genetics* / Q000254:growth & development* / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D008675:Metamorphosis, Biological / Q000235:genetics*; D008969:Molecular Sequence Data; D011986:Receptors, Somatotropin / Q000235:genetics* / Q000378:metabolism
D011986:Receptors, Somatotropin; D007334:Insulin-Like Growth Factor I