Partial characterization of insulin-like peptide(s) in Otala lactea (Mollusca: Pulmonata) and the involvement of the brain in protein and polysaccharide synthesis by the mantle

Insulin-like peptide(s) (ILP) are molecules with structures similar to vertebrate insulin but with yet unspecified function. They have been identified by immunological methods in the central nervous systems (CNS) and the digestive tracts of several molluscan species. Functionally, it has been suggested that the ILPs act in a similar fashion to insulin (i.e. as growth and metabolism factors). The objective of this thesis was to characterize the ILP from the tissues of the pulmonate land snail Otala lactea and to investigate its function. The first chapter deals with the characterization of the ILP using immunocytochemistry, radioimmunoassay (RIA), chromatography and Western blot. Insulin-immunoreactive material with a molecular weight close to that of vertebrate insulin was detected in the CNS and digestive tract of Otala. The hemolymph of active snails contained more ILP than the hemolymph of estivating (dormant) ones. The ILP from the digestive tract appeared to be less hydrophobic than insulin, suggesting structural difference.; In the second chapter, the insulin-immunoreactive material from the CNS and digestive tract was tested for its effect on the in vitro protein synthesis by the mantle edge, the site of shell growth and regeneration. The cerebral ganglia (CG) extract enhanced protein synthesis by the mantle edge. This suggested the presence of a growth factor in the extract. The protein synthesisstimulating activity of two fractions from the CG extract was abolished by porcine insulin antiserum. This suggested the presence in the CG of a growth factor that is related to porcine insulin. Porcine insulin, however, had no significant effect on mantle protein synthesis.; The main function of insulin in vertebrates is the regulation of blood glucose. Chapter 3 investigates the possibility that the ILP of molluscs is also involved in carbohydrate metabolism. Extracts of the CG and the digestive tract were incubated with mantle tissue (site of glycogen synthesis and storage) in the presence of labelled glucose. The extracts did not stimulate in vitro glycogen synthesis. Porcine insulin, on the other hand, enhanced glycogen synthesis by mantle pieces. Mantle glycogen synthesis was inhibited in a dose-dependent manner by the CG extract. The CG extract also activated mantle glycogen phosphorylase (chapter 4). The results from chapters 3 and 4 suggested the presence of a hyperglycemic factor in the CG extract.