Gα Proteins in Drosophila: Structure and Developmental Expression

Abstract

Many of the complex cellular interactions involved in regulating cellular proliferation, determination, and differentiation during development depend on signal transduction processes that allow target cells to alter the expression of specific genes in response to extracellular signals. Given the importance of these inductive interactions, it is likely that many of the genes expressed throughout development and required for accurate specification of cell fate encode molecules that are components of individual signal transduction pathways. Consistent with this notion, a variety of studies have suggested that a number of receptor-mediated signal transduction processes are employed to relay extracellular signals of developmental consequence. Of these signaling mechanisms, the most ancient and diverse involves the coupling of structurally related extracellular receptors to intracellular effectors by means of guanyl nucleotide-binding proteins, or G-proteins. Studies in simple organisms such as yeast (Herskowitz 1989) and Dictyostelium (Firtel et al. 1989) clearly point out the potential significance of this form of sensory transduction in mediating fundamental developmental processes. In both of these systems, the receptors involved possess the typical seven-transmembrane-domain architecture and the G-protein pathways they activate are the exclusive mechanism for conveying developmentally significant signals. In metazoan organisms, the developmental role of G-protein-coupled receptor systems has been more difficult to elucidate, primarily because of the diversity of ligand/receptor systems that utilize this signaling pathway. It has been impossible to predict then, a priori, ligand/receptor interactions that convey developmentally important information. Thus, G-protein-coupled signaling pathways involved in determining cell fate during development remain to be identified systematically.