G-PROTEINS ARE REQUIRED FOR SPATIAL ORIENTATION OF EARLY CELL CLEAVAGES IN C. ELEGANS EMBRYOS

Heterotrimeric G proteins are signal-transducing molecules activated b y seven transmembrane domain receptors. In C. elegans, gpb-1 encodes t he sole G beta subunit; therefore, its inactivation should affect all heterotrimeric G protein signaling. When maternal but no zygotic gpb-1 protein (GPB-1) is present, development proceeds until the first larv al stage, but these larvae show little muscle activity and die soon af ter hatching. When, however, the maternal contribution of GPB-1 is als o reduced, spindle orientations in early cell divisions are randomized . Cell positions in these embryos are consequently abnormal, and the e mbryos die with the normal number of cells and well-differentiated but abnormally distributed tissues. These results indicate that maternal G proteins are important for orientation of early cell division axes, possibly by coupling a membrane signal to centrosome position.