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

Correct placement and orientation of the mitotic spindle is essential for s egregation of localized components and positioning of daughter cells. Altho ugh 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 earl y cell division axes in C. elegans embryos. Here we show that GOA-1 (a G al pha (0)) and the related GPA-16 are the functionally redundant Get subunits and that GPC-2 is the relevant G gamma subunit that is required for spindl e orientation in the early embryo. We show that G alpha and G beta gamma ar e involved in controlling distinct microtubule-dependent processes. G beta gamma is important in regulating migration of the centrosome around the nuc leus and hence in orientating the mitotic spindle. G alpha is required for asymmetric spindle positioning in the one-celled embryo.