The pancreatic islet beta-cell autoantigen of relative molecular mass 64,000 (64K), which is a major target of autoantibodies associated with the development of insulin-dependent diabetes mellitus (IDDM) has been identified as glutamic acid decarboxylase, the biosynthesizing enzyme of the inhibitory neurotransmitter GABA (gamma-aminobutyric acid). Pancreatic beta cells and a subpopulation of central nervous system neurons express high levels of this enzyme. Autoantibodies against glutamic acid decarboxylase with a higher titre and increased epitope recognition compared with those usually associated with IDDM are found in stiff-man syndrome, a rare neurological disorder characterized by a high coincidence with IDDM.

Sensory experience in early life shapes the mammalian brain. An impairment in the activity-dependent refinement of functional connections within developing visual cortex was identified here in a mouse model. Gene-targeted disruption of one isoform of glutamic acid decarboxylase prevented the competitive loss of responsiveness to an eye briefly deprived of vision, without affecting cooperative mechanisms of synapse modification in vitro. Selective, use-dependent enhancement of fast intracortical inhibitory transmission with benzodiazepines restored plasticity in vivo, rescuing the genetic defect. Specific networks of inhibitory interneurons intrinsic to visual cortex may detect perturbations in sensory input to drive experience-dependent plasticity during development.

Three pancreatic beta-cell lines have been established from insulinomas derived from transgenic mice carrying a hybrid insulin-promoted simian virus 40 tumor antigen gene. The beta tumor cell (J3TC) lines maintain the features of differentiated beta cells for about 50 passages in culture. The cells produce both proinsulin I and II and efficiently process each into mature insulin, in a manner comparable to normal beta cells in isolated islets. Electron microscopy reveals typical beta-cell type secretory granules, in which insulin is stored. Insulin secretion is inducible up to 30-fold by glucose, although with a lower threshold for maximal stimulation than that for normal beta cells. (3TC lines can be repeatedly derived from primary beta-cell tumors that heritably arise in the transgenic mice. Thus, targeted expression of an oncogene with a cell-specific regulatory element can be used both to immortalize a rare cell type and to provide a selection for the maintenance of its differentiated phenotype.Pancreatic beta cells synthesize and secrete insulin, a hormone involved in regulation of glucose homeostasis. In rodents there are two nonallelic insulin genes (I and II), which differ in the number of introns as well as in chromosomal location. Both genes are expressed in beta cells (1). An adult murine pancreas contains about 106 beta cells, clustered in the islets of Langerhans, which are dispersed throughout the exocrine tissue. As a consequence, molecular analyses of beta-cell function has in large part depended on in vitro cultures. Cells from isolated islets do not grow well in culture, although they maintain viability for a few weeks (2). In recent years, several lines of transformed beta cells have been generated (3-6). Two of these, RIN-m SF, derived from an x-ray-induced rat insulinoma, and HIT, from hamster islets transformed by simian virus 40, have been used extensively for characterization of insulin gene expression (4,5,7,8).However, it is unclear to what extent they represent normal beta cells, given that the levels of insulin secreted are considerably lower than those of beta cells in vivo.The ability to target expression of oncogenes to particular cells in transgenic mice, by using cell-specific regulatory elements, presents a method for immortalization of rare cell types. We have reported that transgenic mice harboring insulin-simian virus 40 tumor (T) antigen (RIP-Tag) hybrid genes heritably develop beta-cell tumors (9-11). Here we describe the characterization of several beta tumor cell (J3TC) lines obtained from transgenic mouse tumors and propagated in culture for over 60 passages. These cells provide a useful tool for studies of beta-cell regulation and gene expression. METHODSCell Cultures. Pancreatic insulinomas were excised from transgenic mice and disrupted in Dulbecco's modified Eagle's medium (DMEM). To minimize contamination by fibroblasts and other nontransformed cells, the tumors were not trypsinized. Rather, the tumor capsule was gently removed, and the tumor cells were mech...

Fas ligand is believed to mediate immune privilege in a variety of tissues, including the eye, testis, and a subset of tumors. We tested whether expression of Fas ligand on pancreatic islets either following adenoviral or germline gene transfer could confer immune privilege after transplantation. Islets were infected with an adenoviral vector containing the murine Fas ligand cDNA (AdFasL), and were transplanted into allogenic diabetic hosts. Paradoxically, AdFasL-infected islets underwent accelerated neutrophilic rejection. The rejection was T cell and B cell independent and required Fas protein expression by host cells, but not on islets. Similarly, transgenic mice expressing Fas ligand in pancreatic beta cells developed massive neutrophilic infiltrates and diabetes at a young age. Thus, Fas ligand expression on pancreatic islets results in neutrophilic infiltration and islet destruction. These results have important implications for the development of Fas ligand-based immunotherapies.