Molecular biological techniques are being used to discern gene expression of insulin, insulin-like growth factors and their receptors in several vertebrate model systems. Insulin is apparently a requirement for normal development, and the chicken embryo is one of the suitable models for studying the role of insulin in development. The pattern of expression of insulin gene in developing chicken pancreas and in whole embryo at prepancreatic stages is being undertaken. The role of insulin in cell differentiation and gene expression in the eye lens of chick embryo is also being used as a cell model to understand the action of insulin in development. The amphibian, Xenopus laevis, is also a model system used to study development. Previously the amphibian insulin sequenced was unknown. In this laboratory insulin from pancreas of Xenopus has been isolated and its sequence characterized and confirmed by molecular cloning. A transgenic mouse line with multiple copies of the human insulin gene integrated into its genome has been established. The degree of hyperinsulinemia correlates with human gene copy numbers. The transgenic mice provide a model system for studies in regulation of insulin gene expression and the effects of chronic hyperinsulinemia on glucose homeostasis.
