Translation of polarity cues into asymmetric spindle positioning in Caenorhabditis elegans embryos.

Asymmetric divisions are crucial for generating cell diversity; they rely on coupling between polarity cues and spindle positioning, but how this coupling is achieved is poorly understood. In one-cell stage Caenorhabditis elegans embryos, polarity cues set by the PAR proteins mediate asymmetric spindle positioning by governing an imbalance of net pulling forces acting on spindle poles. We found that the GoLoco-containing proteins GPR-1 and GPR-2, as well as the Galpha subunits GOA-1 and GPA-16, were essential for generation of proper pulling forces. GPR-1/2 interacted with guanosine diphosphate-bound GOA-1 and were enriched on the posterior cortex in a par-3- and par-2-dependent manner. Thus, the extent of net pulling forces may depend on cortical Galpha activity, which is regulated by anterior-posterior polarity cues through GPR-1/2.