Intracisternal A-particles in genetically diabetic mice: identification in pancreas and induction in cultured beta cells.
Sucrose density gradient analysis of purified pancreatic homogenates from glycaemic C57BL/Ks diabetes (db/db) mice and their normoglycaemic controls have revealed the presence in the diabetics of increased Mg++-dependent RNA-directed DNA polymerase activity sedimenting with a density of approximately 1.21 g/cm3. Electron microscopy revealed that this fraction contained typical intracisternal A-particles. Purified cultures of pancreatic islet cells 4--7 day old postnatal "misty diabetic" mice and normal siblings were established and then maintained in Eagle's minimal essential medium without serum. Under these conditions, the presence of intracisternal A-particles in beta cells of both mutant and control genotypes was very rare. No change in numbers of intracisternal A-particles was seen after 2--4 days of incubation in Dulbecco's-modified minimal essential medium containing 5.5 mmol/l glucose. However, when the glucose concentration of Dulbecco's medium was elevated to 16.5 mmol/l, ultrastructural changes specific to the beta cell population occurred that were reminiscent of those alterations observed in situ. Intracisternal A-particles were commonly seen in cultured beta cells showing hypersecretion-stress morphology. Since equal numbers of intracisternal A-particles were present in cultured beta cells from normal and mutant mice, it was concluded that the db gene itself was not required for intracisternal A-particle expression. The cell culture results suggest that elevated intracisternal A-particle activity observed in vivo may be produced directly or indirectly by the ambient high blood glucose levels characteristic of this mutant.
D000818:Animals; D004259:DNA-Directed DNA Polymerase / Q000032:analysis; D003920:Diabetes Mellitus / Q000235:genetics / Q000473:pathology*; D005260:Female; D005838:Genotype; D066298:In Vitro Techniques; D002479:Inclusion Bodies / Q000201:enzymology / Q000648:ultrastructure*; D007515:Islets of Langerhans / Q000473:pathology* / Q000648:ultrastructure; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL
D004259:DNA-Directed DNA Polymerase