Spongiform degeneration of the central nervous system is best known as the hallmark of prions, but despite a tremendous body of knowledge regarding the molecular genetics and biochemistry of PrP, the pathophysiologic mechanisms of vacuolation and neuronal cell death are still unknown. We have recently identified two genes in mice, Attractin (Atrn) and Mahoganoid, in which loss-of-function mutations cause recessive inheritance of a neurodegenerative disease whose manifestations are remarkably similar to those caused by gain-of-function mutations in PrP. Both genes were identified because they are also previously existing mouse coat color mutations (Atrn was formerly known as mahogany); studies from our laboratory based on the genetics of pigmentation suggest that Atrn and Mahoganoid are part of a conserved biochemical and cellular pathway that controls ubiquitination and proteasomal degradation. We propose a series of experiments to gain further insight into the pathophysiology of spongiform degeneration in Atrn and Mahoganoid mutant mice, and its relationship to PrP metabolism. Brain sections and homogenates from Atrn and Mahoganoid mutant animals will be examined for evidence of PrP aggregates and proteasomal dysfunction, and genetic and biochemical interaction studies will be carried out to test if neurodegeneration in Atrn or Mahoganoid mutant animals is caused by abnormalities in the production or processing of PrP. A transgenic assay will be developed to assess which domains of Mahoganoid are required to prevent neurodegeneration, and cell biologic studies will be applied to investigate whether Atrn and mahoganoid act in a common subcellular location or share intracellular interaction partners. Finally, the potential for additional or redundant roles in the Atrn-Mahoganoid pathway will be explored by investigating paralogs for each gene. Investigating the biochemical, cellular, and genetic relationships between Atrn, Mahoganoid, and PrP is likely to provide general insight into the pathogenesis of spongy degeneration. ? ?
