Insulin-related receptors in the early chick embryo: from tissue patterns to possible function

Insulin and two closely related peptides, insulinlike growth factors I and II (IGF-I and IGF-II), as well as their respective receptors, overlap in structure, specificity, and function. Very little is known about the role of these peptides and their receptors in embryogenesis. We have found that chick embryo tissues express both insulin and IGF receptors at very early stages of organogenesis. Each type of receptor is regulated throughout embryogenesis in a manner that is tissue-specific. Substances with insulin immunoactivity and bioactivity are detected in chick embryos at prepancreatic stages (days 2 and 3). Embryos that grow in the presence of antiinsulin antibodies (which are known to neutralize the bioactivity of insulin but not that of the IGFs found in adult vertebrates) demonstrate retarded growth and impaired differentiation. These data support the hypothesis that insulin or insulin-related peptides are essential elements for normal development in the chick embryo.