Pancreatic islet immunoreactivity to the Reg protein INGAP

The Reg-related protein family member INGAP (islet neogenesis-associated protein) is a pleiotropic factor enhancing islet neogenesis, neurite growth, beta-cell protection, and beta-cell function. Using an antibody to the N-termini of INGAP, we have identified that immunoreactivity to INGAP localized to the pancreatic endocrine cells in mouse. INGAP- and insulin-immunoreactive cells are mutually exclusive, with INGAP-immunoreactive cells being preserved after streptozotocin-mediated destruction of beta-cells. Glucagon- and INGAP-immunoreactive cells colocalize, although respective antigen expression occurs in different intracellular locations. These data suggest that INGAP-immunoreactive cells include alpha-cells; however, detection of single INGAP-immunoreactive/glucagon-negative cells indicates that this may not be exclusive. In addition to mouse, detection of islet endocrine cells that were INGAP immunoreactive/glucagon immunoreactive/insulin negative was also observed in islets from human, monkey, and rat. These findings reveal that INGAP and/or related group 3 Reg proteins have a conserved expression in the pancreatic islet.