Many cells produce coherent arrays of structures whose orientation is linked to the overall body axes. The existence of coherent arrays implies a mechanism of cell interactions involving local and/or global orienting signals and receptors. The link between cell polarity and pattern formation is indicated by the effects of tissue polarity genes in Drosophila and especially by the dishevelled (dsh) gene. The key observation is that the dsh gene is both a tissue polarity gene and a segment polarity gene. Mutations of dsh disrupt cell polarity throughout the animal and the also disrupt segmental boundaries both in the embryo and in adult limbs. Moreover, some of the polarity disruptions caused by dsh suggest that cell signalling can be directional, thus adding a potentially powerful dimension to the pattern formation process. Two other tissue polarity genes, spiny legs (sple) and frizzled (fz) also affect pattern formation, although the effects are limited to adult structures. Thus, cell polarity and pattern formation appear intimately interrelated. We have examined cell polarity in mutant strains of Drosophila. These studies show that cells receive at least two orienting signals that can be separated genetically by the dsh, sple and fz genes. We propose to carry out a series of molecular and genetic studies to learn more about the mechanism of action of the dsh gene and its gene product and to examine the cellular requirements of the dsh, sple and fz genes in establishing cell polarity. In particular, we will raise antibodies to the dsh protein and determine the distribution and subcellular location of the dsh protein. We will conduct genetic screens to identify dsh mutations and molecular screens to identify homologs and characterize the altered genes at the molecular level as part of structure/function studies of the dsh gene product. We will examine the internal organization of eyes and eye discs which are mosaic for dsh, sple and fz mutants to determine the requirement for each of these genes in the eye. We will study the development of ommatidia in mutant and normal discs using 3 dimensional confocal microscopy. We will test for novel interactions between dsh and other known tissue polarity and segment polarity loci suspected of interaction with dsh and we will screen for new genes and proteins which might interact with dsh. These studies will serve to identify the role of the dsh protein and possibly others in the proposed cell signalling cascade which results in cell polarity. By analogy with related genes, the mechanism of action and possibly the structure of the dsh gene are likely to be highly conserved in evolution and relevant to cell polarity and signalling in other organisms.
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