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Title: Comparing insulin and insulin-like growth factor-1 signalling in myoblasts
Author: Bray, Jonathan Alexander
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2006
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In this study a chimeric receptor system was employed in which the extracellular domain of the TrkC receptor was fused to the intracellular portion of either the insulin (TIR) or IGF-1 (TIGFR) receptor. These chimeric receptors were expressed in separate populations of the skeletal muscle cell line L6. Initial analysis of individual downstream signalling components and assessment of cell proliferation, induced by TIR or TIGFR stimulation revealed little difference between the two chimeras. To more comprehensively screen for potential differences, microarray analysis was used to compare regulation of gene expression by the two chimeric receptors. This led to the identification of several differentially regulated genes.  Whilst it was initially hypothesised that skeletal muscle cells might yield several selectively insulin-sensitive genes, the majority of genes selectively regulated by one receptor were preferentially IGF-1 responsive, consistent with previous studies in other cell types. This perhaps reflects the more mitogenic effect of this ligand in vivo, manifest as an increased ability to regulate transcription per se. Of the differentially regulated genes, that encoding Fit-1m was found to be preferentially induced through activation of the TIGFR rather than the TIR. Further characterisation using real-time PCR established that induction of Fit-1 expression required an intact MAPK signalling pathway. Similar effects were observed when the regulation of Fit-1 expression by insulin and IGF-1 was examined. Subsequent work attempted to establish regions of promoter responsible for the preferential induction of Fit-1m expression by IGF-1. Despite defining promoter and putative enhancer regions which are important for Fit-1m transcription, no region was found which confers a response to stimulation with various ligands, including IGF-1. Rather, a high level of constitutive expression was driven by these DNA sequences, suggesting that an IGF-1 response inhibitory factor may control expression of this gene, binding outside the regions examined. Fit-1 joins an increasing list of genes preferentially regulated by the IGF-1R over the IR and provides and end point with which to analyse potential inherent differences in the signalling capacity of these two highly homologous receptors.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available