Structural, biochemical, and expression analysis of two distinct insulin-like growth factor I receptors and their ligands in zebrafish.
We have cloned and characterized cDNAs encoding the zebrafish IGF ligands and receptors. Sequence comparison showed that the primary structures of zebrafish IGF-I, IGF-II, and IGF-I receptors (IGF-IRs) have been highly conserved in vertebrates. In contrast to the presence of a single IGF-IR gene in mammals, two distinct IGF-IR genes, termed igf-1ra and igf-1rb, were found in zebrafish. Structural and phylogenetic analyses indicated that both genes are orthologous to the human igf-1r gene. Immunoprecipitation studies with specific antibodies showed that both IGF-IR genes are expressed and both receptors bind to IGFs and des(1-3)IGF-I, but not to insulin. The spatio-temporal expression patterns of the two IGF-IRs and their ligands were determined using a combination of RT-PCR, whole mount in situ hybridization, and immunocytochemistry. Transcripts for both IGF-I and -II mRNAs were found throughout embryogenesis in a ubiquitous manner. In adult tissues, IGF-I mRNA was more abundant in liver and testis, and its level was increased after GH treatment, whereas IGF-II mRNA was not regulated by GH. IGF-IRa and IGF-IRb mRNAs and proteins were expressed in overlapping spatial domains, but exhibited distinct temporal expression patterns. In particular, the relative level of IGF-IRa mRNA was low during early embryogenesis and increased in the hatched larva, whereas the situation was reversed for IGF-IRb mRNA. In adult zebrafish, the overall tissue distribution patterns of the two IGF-IRs were similar, but there were differences in their cellular localization and relative abundance in defined cells/regions. The differential expression pattern of IGF-IRa and IGF-IRb suggest that they may play distinct roles in regulating the growth and development of zebrafish.
Maures
Travis
T
Department of Molecular, Cellular and Developmental Biology, Natural Science Building, University of Michigan, Ann Arbor, MI 48109, USA.
Chan
Shu Jin
SJ
Xu
Bin
B
Sun
Hanshi
H
Ding
Jun
J
Duan
Cunming
C
D000595:Amino Acid Sequence; D000818:Animals; D003001:Cloning, Molecular; D017931:DNA Primers; D018076:DNA, Complementary / Q000096:biosynthesis / Q000235:genetics; D018507:Gene Expression Regulation, Developmental / Q000235:genetics*; D006128:Growth / Q000235:genetics* / Q000502:physiology; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D007334:Insulin-Like Growth Factor I / Q000096:biosynthesis / Q000235:genetics; D007335:Insulin-Like Growth Factor II / Q000096:biosynthesis / Q000235:genetics; D007814:Larva / Q000378:metabolism; D008024:Ligands; D008969:Molecular Sequence Data; D010455:Peptides / Q000138:chemical synthesis; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D017526:Receptor, IGF Type 1 / Q000096:biosynthesis* / Q000737:chemistry / Q000235:genetics*; D011972:Receptor, Insulin / Q000096:biosynthesis / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013002:Somatomedins / Q000096:biosynthesis / Q000235:genetics; D014018:Tissue Distribution; D015027:Zebrafish; D029961:Zebrafish Proteins / Q000096:biosynthesis / Q000235:genetics
D017931:DNA Primers; D018076:DNA, Complementary; C511797:IGF1RA protein, zebrafish; C511798:IGF1RB protein, zebrafish; D008024:Ligands; D010455:Peptides; D012333:RNA, Messenger; D013002:Somatomedins; D029961:Zebrafish Proteins; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II; D017526:Receptor, IGF Type 1; D011972:Receptor, Insulin