Distinct roles for G alpha and G beta gamma in regulating spindle position and orientation in Caenorhabditis elegans embryos

Correct placement and orientation of the mitotic spindle is essential for segregation of localized components and positioning of daughter cells. Although these processes are important in many cells, few factors that regulate spindle placement are known. Previous work has shown that GPB-1, the G beta subunit of a heterotrimeric G protein, is required for orientation of early cell division axes in C. elegans embryos. Here we show that GOA-1 (a G alpha sub(o)) and the related GPA-16 are the functionally redundant G alpha subunits and that GPC-2 is the relevant G gamma subunit that is required for spindle orientation in the early embryo. We show that G alpha and G beta gamma are involved in controlling distinct microtubule-dependent processes. G beta gamma is important in regulating migration of the centrosome around the nucleus and hence in orientating the mitotic spindle. G alpha is required for asymmetric spindle positioning in the one-celled embryo.