The long term goal of this work is to understand the role of M-CSF-initiated signaling pathways in osteoclast differentiation and function. It is believed that such information may be important in the diagnosis of specific disease states of bone, and also in the development of new therapies to treat diseases of the bone. The approach is to use transgenic animal models to define and study specific signal transduction pathways activated by M-CSF. In particular, ras proto-oncogene-dependent signaling pathways will be the initial focus of this work. Genes that suppress ras proto-oncogene activity in vitro will be introduced into the monocyte/osteoclast lineage through the use of tissue specific promoters. It is expected that such a strategy should produce osteopetrosis in the transgenic mouse, similar to the disease found in the classic mouse op mutation. The specific aims are: 1) to make transgenic mouse lines that express dominant inhibitors of ras-dependent M-CSF signaling pathways that we have defined using in vitro tissue culture system into the osteoclast lineage. Examples of such inhibitors are the carboxy]-terminal portion of the GTPase-activating protein and an ets 2-lacZ transcriptional repressor. The tissue-specific promoters for the M-CSF receptor gene and the tartrate-resistant acid phosphatase gene will be used to target expression of the transgene to two different periods of osteoclast differentiation. 2) To fully characterize the pathology of the resulting transgenic animals 3) To study the molecular and cellular biology of the abnormal monocytes and osteoclasts produced in the transgenic animals. This will include studies on cell surface markers, patterns of gene expression, and studies of osteoclast differentiation and function in vitro. These studies should yield new insights into the role of ras signaling pathways in osteoclast function and differentiation. They should also provide a framework for studying other hormonal effects on bone using similar strategies, including for example the roles of vitamin A and D and their receptors on bone remodeling.