DOUBLE-LABEL IMMUNOFLUORESCENCE STUDY OF GLUTAMIC-ACID DECARBOXYLASE IN THE FETAL AND ADULT OVINE PANCREAS BY LIGHT AND CONFOCAL MICROSCOPY- EVIDENCE FOR PREDOMINANT BETA-CELL COEXPRESSION

Glutamic acid decarboxylase (GAD) is present in the central nervous sy stem and in several nonneuronal tissues including the pancreatic islet s. There are two isoforms with molecular weights of 65 kDa (GAD65) and 67 kDa (GAD67). The cellular specificity of the two molecular forms o f GAD and their levels within the mammalian islets may be species-depe ndent, being coexpressed in both beta and in non-beta cells. We have e xamined the ovine pancreas, from the adult and fetal stages of late ge station, for the expression of GAD65 within the islet cells by double- label immunofluorescence light and confocal microscopy. In the adult t issue, GAD65 was colocalized in a majority of the beta cells (>95%), w ith only a few glucagon and somatostatin cells (<5%) showing immunoloc alization. During the fetal stages GAD65 also showed a similar predomi nant beta-cell coexpression. The enzyme was also detected in a few fet al glucagon (<5%) but not somatostatin cells. In the degenerating larg e fetal islets, GAD65 was also observed in the majority of the residua l beta cells. These results demonstrate that in the ovine pancreas GAD 65 is expressed during fetal development and is predominantly beta-cel l-restricted. This pattern of expression is maintained during adult li fe. However, the physiological role of pancreatic GAD and/or its biosy nthetic product, gamma-aminobutyric acid, in islet function in the she ep and in other ruminants remains unclear. (C) 1997 Academic Press.