The Hedgehog (HH) family of secreted signaling proteins is important for a number of critical patterning events in both vertebrate and invertebrate embryogenesis. HH was first identified in Drosophila, in the classic screen by Nusslein-Volhard and Wieschaus. Since then, related mammalian proteins have been found to play multiple, essential roles in development and tumorignesis. Study of HH proteins has contributed fundamental insights into novel mechanisms of proteolysis and post-translational protein modification. Furthermore, analyses of the intracellular signaling pathway that is stimulated upon interaction of HH with its cellular receptors has resulted in rapid elucidation of a new and important signal transduction mechanism. Dr. Montell and others have found that HH signaling influences cell fates in the Drosophila ovary, which is emerging as an important model system for studies of cell fate specification and cell cycle regulation. Specific somatic cells known as polar cells are specified by HH signaling, early in oogenesis. Anterior polar cells subsequently recruit 4-8 additional follicle cells to become migratory "border cells". In a screen for mutations that affect border cells in mosaic clones, Dr. Montell's laboratory identified two mutations, one on chromosome 2R and one on 2L, that caused a dramatic increase in the numbers of border cells. In both cases, the increase could be attributed to increases in the numbers of polar cells, a phenotype that is also observed when HH is over-expressed. These findings suggest that the new mutations might affect genes whose normal role is in negative regulation of the HH signaling pathway. One of the mutations is an allele of costal-2 (cos2), a locus previously known to play a role in negative regulation of the HH pathway. The second mutation appears to affect a previously unknown locus, since it maps to a region that does not contain a known negative regulator of the HH pathway. This new locus has tentatively been named moh for modulator of hedgehog signaling. Dr. Montell plans to test the hypothesis that moh modulates HH signaling, either directly or indirectly. The specific aims of this proposal are: 1) to ascertain what step in the HH pathway is affected by the moh mutation; 2) to identify and sequence the transcript corresponding to the mutated gene and search for related genes in mammals; 3) to characterize the MOH protein product; and 4) to carry out additional screening for negative regulators of the HH pathway in the ovary. Since previous screens for HH pathway mutants have focussed on embryonic and adult viable phenotypes, there may be additional components of the pathway that can only be identified using mosaic analysis.
