During the development of a multi-cellular organism, communication between cells influences the pattem of development. A great deal of research has focused on deciphering the molecular mechanisms responsible for such communication. Studies with model systems such as Drosophila and C. elegans show that a variety of cell-cell interactions involve evolutionarily conserved proteins of the Notch family. The Notch proteins function as cell-surface receptors that respond to specific cell-surface ligands. Although Notch proteins and their associated ligands are used by interacting cells in many different systems, including humans, very little is known about other molecules involved in these events. A genetic approach to identifying new components of Notch-mediated interactions has proven successful in C. elegans where two new genes, aph-1 and aph-2, have been identified. The aph-1 and aph-2 gene products appear to be necessary, along with the conserved Notch receptor and its ligand, to mediate cellular induction in at least two specific incidences in early embryogenesis. The general goal of this proposal is to determine what role these two gene products have in facilitating cellular communication. Three specific approaches will be used: First, biochemeical and molecular analysis will be used to further our understanding of the aph-2 gene product. Previous work showed that the aph-2 gene encodes a novel extracellular protein associated with the cell surface. The work presented here aims at analyzing the molecular interactions between the APH-2 protein, the cell surface, the Notch receptor protein, and its associated ligand. Second, molecular characterization of the aph-1 gene product will begin with its cloning and sequencing to determine the nature of the aph=l product. Third, a genetic approach will be used to search for additional gene products that interact with the aph=l and aph=2 gene products. Genetic screens are described that are specifically designed to isolate genes that participate with aph -1 or aph-2 in mediating cell-cell interactions. Together these experiments represent straightforward molecular and genetic approaches to learning about new components of the Notch-mediated mechanism of cell-cell interactions that occur throughout the animal kingdom.
