Afshar, K.Willard, F. S.Colombo, K.Johnston, C. A.McCudden, C. R.Siderovski, D. P.Gönczy, P.2006-08-242006-08-242006-08-24200410.1016/j.cell.2004.09.026https://infoscience.epfl.ch/handle/20.500.14299/23378615479639Heterotrimeric G proteins are crucial for asymmetric cell division, but the mechanisms of signal activation remain poorly understood. Here, we establish that the evolutionarily conserved protein RIC-8 is required for proper asymmetric division of one-cell stage C. elegans embryos. Spindle severing experiments demonstrate that RIC-8 is required for generation of substantial pulling forces on astral microtubules. RIC-8 physically interacts with GOA-1 and GPA-16, two Galpha subunits that act in a partially redundant manner in one-cell stage embryos. RIC-8 preferentially binds to GDP bound GOA-1 and is a guanine nucleotide exchange factor (GEF) for GOA-1. Our analysis suggests that RIC-8 acts before the GoLoco protein GPR-1/2 in the sequence of events leading to Galpha activation. Furthermore, coimmunoprecipitation and in vivo epistasis demonstrate that inactivation of the Gbeta subunit GPB-1 alleviates the need for RIC-8 in one-cell stage embryos. Our findings suggest a mechanism in which RIC-8 favors generation of Galpha free from Gbetagamma and enables GPR-1/2 to mediate asymmetric cell division.AnimalsCaenorhabditis elegans/cytology/*physiologyCaenorhabditis elegans Proteins/genetics/*metabolismCell Division/*physiology*EmbryoNonmammalian/cytology/physiologyEnzyme ActivationEpistasisGeneticGTP-Binding Protein alpha Subunits/metabolismGuanine Nucleotide Dissociation Inhibitors/genetics/metabolismGuanine Nucleotide Exchange Factors/genetics/metabolismMicrotubules/metabolismMitotic Spindle Apparatus/metabolismNuclear Proteins/genetics/*metabolismProtein BindingRNA InterferenceResearch SupportNon-U.S. Gov'tResearch SupportU.S. Gov'tP.H.S.StressMechanicalTwo-Hybrid System Techniquestext::journal::journal article::research article