This proposal concerns the development and analysis of mouse models for the study of the neurofibromatosis gene product and its role in the development of the nervous system. Von Recklinghausen's neurofibromatosis type l (NF-I) is a dominant autosomal disorder that strikes one in three thousand individuals. It is characterized by anomalies of diverse cell types, many of which are of the neural crest lineage. The severity of these phenotypes can vary greatly. However, schwannomas often mature into malignant neurofibrosarcomas. The NF-I gene product, neurofibromin, is a cytoplasmic protein of approximately 3000 amino acids that exhibits structural and functional homology to the super family of GTPase activating (GAP) proteins that function as negative regulators of ras oncoproteins. We have generated a mouse model that is specifically and exclusively mutated in the NF-I gene thus enabling us to investigate the action of NF- I in the development of the nervous system. Our results indicate that sensory and sympathetic neurons which normally require neurotrophins (NGF, BDNF, NT-3 & NTA/5) for their normal development and survival, escape this requirement when the NF-I gene has been ablated. This exciting finding implicates neurofibromin as a functional intermediary in neurotrophin signalling and provides a unique system for testing the role of this tumor suppressor protein in the regulation of neuronal signals that are transmitted from neurotrophins to maintain neurons alive. We propose four specific aims: 1) to characterize the consequences of neurofibromin loss for neurotrophin-dependent neuronal survival in primary neuronal culture assays. 2) We will use genetic approaches to dissect the signalling intermediates that function through the neurotrophin/NF-l pathway. This will be accomplished with the use of adenovirus gene delivery vectors of oncogenes such as ras and raf. 3) We will intercross the NF-l mutation into each of the neurotrophin (Trk) receptor and neurotrophin mutation knockouts that were generated in our laboratory. Analysis of the neurons from double mutants should allow us to determine the location of NF-I in the neurotrophin signalling pathway and the direct effect of this gene on trk neurotrophin mediated signalling. 4) NF-1 transgenic mice will be generated and crossed into the NF knockouts in the effort to obtain partial rescue of the embryonic lethality to enable analysis of mutant neurons in late embryonic stages. The availability of reliable in vivo models to study the role of neurofibromin in neurotrophin function is of critical importance for further evaluation of this suppressor oncogene in human disease, in programmed cell death, and in neural development.
