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Cloning of the chicken insulin receptor substrate 1 gene
M Taouis1, S I Taylor, M Reitman
1Institut National de la Recherche Agronomique, Station de Recherches Avicoles, Nouzilly, France.
Abstract:
The action of insulin, IGF-1, and IGF-2 is mediated via two receptor tyrosine kinases, the insulin and IGF-1 receptors. Upon ligand binding, these receptors become active kinases, undergoing autophosphorylation and phosphorylating cellular substrates, including insulin receptor substrate-1 (IRS-1). IRS-1 acts as a docking protein and mediates multiple interactions among other proteins, resulting in transduction of the metabolic and mitogenic signals. The IRS-1 gene has been cloned from four species (human, rat, mouse, and frog). In the present study, the chicken IRS-1 gene was cloned. Chicken, as is true of birds in general, have a higher fasting and fed blood glucose than do mammals. Chicken IRS-1 DNA sequence encodes a 1240 amino acid protein. The most conserved regions were the IRS homology-2 (IH-2), the pleckstrin homology, and the shc and IRS-1 NPXY-binding (SAIN) domains. Twelve of the cIRS-1 tyrosine residues are in sequence motifs that, when phosphorylated, could interact with proteins containing SH2 domains. All twelve of these motifs were conserved. IRS-1 mRNA is expressed during embryogenesis in chicken and persists after hatching. In LMH cells, derived from a chicken hepatoma, two bands were tyrosine phosphorylated in an insulin-dependent manner: IRS-1 (approximately 180 kDa) and the insulin receptor beta subunit (approximately 95 kDa). Chicken IRS-1 is structurally and functionally similar to its human homolog, despite the difference in blood glucose levels and the evolutionary distance between birds and mammals.
Insights
Researchers cloned the chicken insulin receptor substrate-1 (IRS-1) gene, revealing conserved protein domains crucial for signaling. This finding highlights functional similarities between chicken and human IRS-1, despite evolutionary differences.
Area of Science:
- Molecular Biology
- Biochemistry
- Comparative Genomics
Background:
- Insulin and IGF-1/2 signaling pathways are vital for cellular metabolism and growth.
- These pathways are mediated by receptor tyrosine kinases, including the insulin receptor and IGF-1 receptor.
- Insulin receptor substrate-1 (IRS-1) acts as a key docking protein, transducing signals from these receptors.
Purpose of the Study:
- To clone and characterize the chicken IRS-1 gene.
- To investigate the structural and functional conservation of chicken IRS-1 compared to mammalian homologs.
- To explore the role of IRS-1 in chicken cellular signaling.
Main Methods:
- Cloning of the chicken IRS-1 gene.
- DNA sequencing and protein analysis to identify conserved domains.
- Analysis of IRS-1 mRNA expression during chicken embryogenesis and post-hatching.
- Insulin-dependent tyrosine phosphorylation assays in LMH cells.
Main Results:
- The chicken IRS-1 gene encodes a 1240 amino acid protein.
- Highly conserved regions include the IRS homology-2 (IH-2), pleckstrin homology, and SAIN domains.
- Twelve conserved tyrosine residues in SH2-binding motifs were identified.
- IRS-1 mRNA is expressed during embryogenesis and after hatching.
- Insulin treatment induced tyrosine phosphorylation of chicken IRS-1 (180 kDa) and the insulin receptor beta subunit (95 kDa) in LMH cells.
Conclusions:
- Chicken IRS-1 shares significant structural and functional similarity with its human counterpart.
- Conserved domains and phosphorylation sites suggest a conserved role in insulin signaling.
- These findings provide insights into avian glucose metabolism regulation despite higher blood glucose levels in birds.