Since the cloning of the neurofibromatosis 1 (NF1) gene, which is responsible for type I neurofibromatosis, much has been learned about the mechanism by which the encoded protein (called Neurofibromin) controls the growth and proliferation of cells within peripheral nerve sheaths (the insulating cover around peripheral nerves). However, many unanswered questions remain as to precisely how NF1 exerts this control of cell growth. For example, it is not completely established how the activity of Neurofibromin itself is regulated. Also, probably many proteins may cooperate with Neurofibromin in growth control that have not yet been identified. Finally, the observation that individuals with neurofibromatosis can exhibit the disorder with varying degrees of severity suggests the existence of other regulatory pathways that also may affect peripheral nerve growth. These pathways also have not been identified.

In other studies involving growth and development, questions such as these have been answered with what is known as a model genetic system. A model genetic system is an organism that is much less complicated than humans, but which can display the particular disorder in question. With such a system, the questions described above can be most easily addressed, and the answers can then be applied to humans. These studies can thus add greatly to our knowledge of the disease process as well as enable the identification of many additional targets for pharmacological treatment. We and others have provided evidence that the fruit fly Drosophila melanogaster can be a model genetic system for the study of neurofibromas: a Drosophila gene also called NF1 is very similar to its human counterpart, and the Drosophila peripheral nerve has a structure and function very similar to its human counterpart. Furthermore, we recently found that Drosophila mutants lacking NF1 or any of five additional genes exhibit overgrowth within peripheral nerves reminiscent of neurofibromas. One of these additional genes is Drosophila Ras, previously shown to be an important target of Neurofibromin in humans. This provides us with additional confidence that the Drosophila "nerve growth" system might faithfully emulate the human system. Other genes identified, such as Drosophila push, were not previously suspected to be involved in nerve growth control. This provides us with additional confidence that the Drosophila system can identify new regulators of growth and provide new targets for drug therapy.

We propose to continue studying the control of peripheral nerve growth in the fly model system to learn more about the regulatory pathways by which growth is controlled. In our first aim, we will use mutant and transgenic Drosophila to test the emerging possibility that NF1 regulates peripheral nerve growth in part by activating a signaling molecule called protein kinase A (PKA). If true, this would raise the possibility that PKA might be a useful target for drug treatment. In our second aim, we will generate transgenic Drosophila carrying various mutant derivatives of NF1 to help identify which regions of Neurofibromin perform particular growth-regulating functions within the peripheral nerve. In our third aim, we will try to define more precisely how the novel growth-regulating protein Push acts together with Neurofibromin, Ras, and PKA to regulate peripheral nerve growth. In our fourth aim, we will identify which of the large number of proteins that are known to function along with Ras in growth control are actually responsible for growth control within nerves and which are dispensable.

Such studies on Drosophila are expected to provide more information on precisely how peripheral nerve growth is controlled and how Neurofibromin and its partner proteins act in that process. In particular, our first, third, and fourth aims are likely to provide a large number of new proteins that regulates nerve growth and could potentially serve as new targets for drug treatment.