Pattern formation requires that cells have a unique positional value relative to their neighbors but positional value alone is not sufficient to account for the fine tuning of the patterns observed. The exquisitely precise organization of many cellular arrays demonstrates that cells are also oriented relative to their neighbors to form parallel arrays of structures and that this cellular orientation is linked to the overall organization of the body plan. This is most easily appreciated by considering the organization of parallel arrays of cellular structures seen in many tissues such as the parallel orientation of hairs and bristles, the repeated orientation of the rhabdomeres of the eye, and the polar organization of the cells of sensilla and the polarized induction of bracts by machrochate forming cells. In all these cases the microorganization of the cells of each structure is linked to the global orientation of the general body plan. The mere existence of this level of organization implies a mechanism of signals and receptors. In some way cells must receive not only positional cues but orienting cues that serve to link their orientation to that of the general body plan. Dr. Marsh has been investigating the mechanisms whereby orienting information is transmitted to cells. He has surveyed a number of mutants for affects on tissue organization and cell polarity. The dishevelled gene appears to affect cell orientation in a global manner. He had found that dishevelled mutants affect orientation of bract induction by bristle cells, orientation of hairs and bristles and organization of the rhabdomeres of the eye. He is proposing to clone and analyze the dishevelled locus.
