all of these are also activated in most KIT- mutant GISTs (Fig. 3) (18). The PDGFRA- mutant GISTs lacked expression of phos- phoStat5 despite strong expression of total Stat5, which is also typical of KIT-mutant GISTs. We also compared the cytogenetic profiles of four PDGFRA-mutant GISTs and 52 KIT-mutant GISTs. KIT mutations are early events in GIST tumorigenesis, whereas cytogenetic aberrations occur later in disease progression (8). Most of these GISTs, regard- less of PDGFRA or KIT mutation, featured noncomplex karyotypes with deletions of chromosome 1p and with monosomies of chromosomes 14 and 22 (table S1 and fig. S7). Hence, our studies suggest that the mechanisms of cytogenetic progression and oncoprotein-driven signal transduction are similar in GISTs expressing oncogenic forms of PDGFRA and KIT. We conclude that activating mutations of KIT or PDGFRA are mutually exclusive on- cogenic events in GISTs and that these mu- tations have similar biological consequences. Our data also highlight a crucial role for PDGFRA in the pathogenesis of a solid tu- mor. Notably, a translocation involving the BCR and PDGFRA genes has been described in BCR-ABL–negative chronic myelogenous leukemia and is predicted to result in dimer- ization and kinase activation of the fusion protein (19). PDGFRA is widely expressed in human tissues, so it will be important to determine whether PDGFRA mutations play a role in other human malignancies. Such tumors could be sensitive to Gleevec and other small-molecule drugs that inhibit PDG- FRA kinase activity (20–22). References and Notes 1. M. Miettinen, J. Lasota, Virchows Arch. 438,1(2001). 2. S. Hirota et al., Science 279, 577 (1998). 3. D. A. Tuveson et al., Oncogene 20, 5054 (2001). 4. A. T. van Oosterom et al., Lancet 358, 1421 (2001). 5. G.D.Demetri etal., N.Engl.J.Med. 347,472(2002). 6. M. Taniguchi et al., Cancer Res. 59, 4297 (1999). 7. B. P. Rubin et al., Cancer Res. 61, 8118 (2001). 8. M.C.Heinrich,B.P.Rubin,B.J.Longley,J.A.Fletcher, Hum. Pathol. 33, 484 (2002). 9. J. D. Huizinga et al., Nature 373, 347 (1995). 10. A. Oliveira, J. A. Fletcher, data not shown. 11. Single-letterabbreviationsforaminoacidresidues:A, Ala;C,Cys;D,Asp;E,Glu;F,Phe;G,Gly;H,His;I,Ile; K,Lys;L,Leu;M,Met;N,Asn;P,Pro;Q,Gln;R,Arg;S, Ser; T, Thr; V, Val; W, Trp; and Y, Tyr. 12. B. J. Longley, M. J. Reguera, Y. Ma, Leuk. Res. 25,571 (2001). 13. H. Nagata et al., Proc. Natl. Acad. Sci. U.S.A. 92, 10560 (1995). 14. Q. Tian, H. F. Frierson Jr., G. W. Krystal, C. A. Moskaluk, Am. J. Pathol. 154, 1643 (1999). 15. Y. Yamamoto et al., Blood 97, 2434 (2001). 16. K. Spiekermann et al., Blood 100, 3423 (2002). 17. C. L. Corless, M. C. Heinrich, data not shown. 18. A. Duensing, J. A. Fletcher, data not shown. 19. E. J. Baxter et al., Hum. Mol. Genet. 11,1391(2002). 20. E. Buchdunger et al., J. Pharmacol. Exp. Ther. 295, 139 (2000). 21. N. A. Lokker, C. M. Sullivan, S. J. Hollenbach, M. A. Israel, N. A. Giese, Cancer Res. 62, 3729 (2002). 22. L. Sun et al., J. Med. Chem. 43, 2655 (2000). 23. WethankA.Oliveira,C.Tsao,M.Hibbard,andR.Ruiz for assistance in validating the panRTK screening methods; S.-E. Yen and D. Tsao for invaluable collaborationindevelopingthepanRTKantisera;B. McConarty, J. McCarthy, T. Morgan, M. Gorman, and M. Thyne for assistance with GIST cytogenet- ics; A. Kazlauskas for PDGFRA cDNA; and F. Medei- ros and J. Corson for discussions and correlative studies of GIST pathology. Supported by a Merit Review Research Grant from the Department of Veterans Affairs (M.C.H.), a Deutsche Krebshilfe Fellowship (A.D.), and the Janice and Michael Burke Leiomyosarcoma Research Fund (G.D.D. and J.A.F.). Supporting Online Material www.sciencemag.org/cgi/content/full/1079666/DC1 Materials and Methods Figs. S1 to S7 Table S1 References 22 October 2002; accepted 13 December 2002 Published online 9 January 2003; 10.1126/science.1079666 Include this information when citing this paper. Spongiform Degeneration in mahoganoid Mutant Mice Lin He, 1 Xin-Yun Lu, 3 Aaron F. Jolly, 4 Adam G. Eldridge, 2 Stanley J. Watson, 3 Peter K. Jackson, 2 Gregory S. Barsh, 1 * Teresa M. Gunn 4 * mahoganoid is a mouse coat-color mutation whose pigmentary phenotype and genetic interactions resemble those of Attractin (Atrn). Atrn mutations also cause spongiform neurodegeneration. Here, we show that a null mutation for mahoganoid causes a similar age-dependent neuropathology that includes many features of prion diseases but without accumulation of protease-resistant prion protein. The gene mutated in mahoganoid encodes a RING-containing protein with E3 ubiquitin ligase activity in vitro. Similarities in phenotype, expression, and genetic interactions suggest that mahoganoid and Atrn genes are part of a conserved pathway for regulated protein turnover whose function is essential for neuronal viability. Pigment-type switching in mice is a model system for several aspects of cell and animal physiology in which a paracrine ligand, Ag- outi protein, binds to the melanocortin-1 re- ceptor (Mc1r) and Attractin (Atrn), causing melanocytes to produce yellow instead of black pigment (1–5). Mutations in Agouti, Mc1r, or Atrn cause the “classical” coat color mutations nonagouti, extension, or mahoga- ny, respectively (6 ). Loss of function for Agouti or Mc1r affects only pigmentation, but loss of function for Atrn causes spongi- form encephalopathy, hypomyelination, and body tremor (7–10). mahoganoid is another coat-color muta- tion whose pigmentation is very similar to that of Atrn (formerly mahogany)(11–13). Both mutations lie in the same epistasis group and suppress obesity caused by ectopic brain expression of Agouti (14 ). To investigate whether the gene mutated in mahoganoid carries out a neuronal function similar to that of Atrn, we examined two alleles of mahog- anoid that differ in their effects on coat color (fig. S1). Animals carrying the orig- inal allele, md, synthesize small amounts of yellow pigment on the flank and the ven- trum and do not develop spongy degenera- tion up to 5 months of age (15, 16 ). How- ever, animals carrying the md nc allele (orig- inally known as nonagouti curly) develop progressive spongiform changes, first ap- parent in the hippocampus CA3 region at 2 months of age and later extending to mul- tiple regions of the brain (Fig. 1A and fig. S1). Vacuolation predominates in gray mat- ter and is associated with neuronal loss but preservation of tissue architecture; the ce- rebral cortex, hippocampus, thalamus, brain stem, caudate-putamen, and cerebel- lum granule layer are the most consistently affected regions. These pathological fea- tures are nearly identical to those of Atrn mg- 3J/Atrn mg-3J mutants, although the onset of neurodegeneration and its age-dependent pro- gression in md nc /md nc animals are delayed compared to that of Atrn mg-3J /Atrn mg-3J . By 11 to 12 months of age, many brain regions of md nc /md nc and Atrn mg-3J /Atrn mg-3J mice exhibit moderate to severe astrocytosis, the extent of which correlates with the degree of vacuolation and neuronal cell loss (Fig. 1B). In md nc /md nc mice at 10 months of age, some regions of the deep cortex and lateral thalamus exhibit mild astrocytosis before the formation of microscopically visible vacuoles. Electron microscopy showed that most vacuoles in the 1 Department of Pediatrics, Department of Genetics, Howard Hughes Medical Institute, 2 Department of Pathology, Stanford University School of Medicine, Stanford, CA 94305, USA. 3 Mental Health Research Institute, University of Michigan School of Medicine, Ann Arbor, MI 48109, USA. 4 Department of Biomed- ical Sciences, T4 018 VRT, Cornell University, Ithaca, NY 14853, USA. *To whom correspondence should be addressed. E- mail: gbarsh@cmgm.stanford.edu (G.S.B.); tmg25@ cornell.edu (T.M.G.) R EPORTS 31 JANUARY 2003 VOL 299 SCIENCE www.sciencemag.org 710 on August 7, 2017 http://science.sciencemag.org/ Downloaded from