Transmissible spongiform encephalopathy in the gray tremor mutant mouse.

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Abstract
Gray tremor (gt) is an autosomal recessive mutation in the mouse linked to caracul (Ca) on chromosome 15. The complex mutant phenotype includes pigmentation defects, tremor, seizures, hypo- and dysmyelination in central and peripheral nervous sytems, spongiform encephalopathy and early death. The heterozygote (+/gt) is phenotypically normal but develops a mild spongiform encephalopathy from 2 mo. of age onward. The pigmentation and myelination disorders indicate that the gt genetic locus is active neonatally and probably earlier. The later-expressed vacuolating disorder, which most closely mimics in tissue distribution, histopathology and ultrastructure the spongiform encephalopathies caused by unconventional transmissible agents was studied. This lesion was produced in genetically normal mice in a transmission experiment: of 99 neonatal mice inoculated intracerebrally with gt/gt brain homogenate, all 7 mice of 3 strains (BALB/cBy, C3HeB/FeJ and C57BL/6J) allowed to survive for the unusually long interval of 682-721 days after inoculation, developed spongiform changes distributed as in the mutant phenotype. The gray tremor mutant presents a naturally occurring spongiform encephalopathy whose expression is determined by the interaction of genetic factors and a transmissible agent [slow virus].