Glucagon-like peptide-1 is a fragment of proglucagon secreted by intestinal L-cells. It has potent glucose-dependent insulin secretory effects and also suppresses gastric acid secretion in the stomach. The biological actions of GLP-1 are mediated by the GLP-1 receptor, the structure of which has recently been determined. Defects in insulin secretion are a common feature of NIDDM and as such the GLP-1 receptor is a candidate for contributing to the development of this clinically and genetically heterogeneous disorder. As a first step in determining the role of the GLP-1 receptor in the development of NIDDM, we have isolated the human GLP-1 receptor gene and mapped it to chromosome 6, band p21.1, using the technique of fluorescence in situ hybridization. We also identified a simple tandem repeat DNA polymorphism in the human GLP-1 receptor gene of the form (TG)n. This DNA polymorphism has 14 alleles and a heterozygosity of > 0.8. We have used this DNA polymorphism to localize the GLP-1 receptor gene within the genetic map of the short arm of chromosome 6. This DNA polymorphism will facilitate genetic studies of the contribution of the GLP-1 receptor gene to impaired beta-cell function and NIDDM.
The human parathyroid hormone gene (PTH) was mapped to the 11p15 chromosomal band by in situ hybridization. Using the same procedures and cells, the closely linked β-hemoglobin gene (HBB), the Harvey-ras 1 proto-oncogene (HRASl), and the insulin gene (INS) were also mapped to this same region. Some reports have demonstrated differences in regional localization of the latter three genes, and linkage and molecular studies have not resolved how far this linkage group extends from p15 toward the centromere on the physical gene map. Our results show that all of these genes are localized at llpl5, a region of one chromosomal band that appears to comprise a genetic distance of more than 20 cM.
The genes coding for insulin-like growth factors I and II and epidermal growth factor have been localized to human chromosomes 12q22→q24.1, 11p15, and 4q25→q27, respectively.
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