Peptide growth factors such as nerve growth factor (NGF) and epidermal growth factor (EGF) have well-defined effects on specific populations of embryonic and adult cells. Despite extensive biochemical characterization of these molecules and their effects on cells expressing NGF and EGF receptors, essentially nothing is known about their physiological sites of synthesis during development. In addition, although abnormal synthesis of these factors has been implicated in the pathology of specific inherited diseases such as neurofibromatosis, direct evidence has not yet appeared. In this proposal, we outline our plans to use recently isolated recombinant DNA probes to EGF and to the B-subunit of NGF to address these questions. 1. We will determine the levels of B-NGF and EGF mRNA in polyA-RNA extracts of embryonic and adult tissues. We will use solid-phase DNA-RNA hybridization techniques to quantitate the levels of growth factor mRNA present in these extracts and compare the levels of these mRNA throughout development. 2. We will concurrently locate specific cells types containing NGF and EGF mRNA in embryonic and adult tissue sections using in situ hybridization. We will focus on regions that have previously been suggested as putative synthetic sites for these growth factors or that contain EGF and NFG mRNA as determined by solid-phase DNA-RNA hybridization studies. 3. We will determine whether B-NGF mRNA and EGF mRNA are present in neurofibromas and localize specific cells containing these growth factors with in situ hybridization. We will quantitate the levels of growth factor mRNA present in different neurofibroma types including stable and rapidly growing neurofibromas, plexiform neurofibromas, and acoustic neuromas. Taken together, these studies will allow us to determine when NGF and EGF gene expression normally occurs during embryogenesis and whether altered growth factor mRNA levels are associated with specific neurofibromatoma types.