The Rho family of small GTPases, including RhoA, Rac and Cdc42 plays an important role in the regulation of cell morphology and gene expression. For example, the stimulation of RhoA leads to the formation of actin stress fibers, neurite retraction and cell rounding. Here, we report the identification of a novel C.elegans RhoGEF (T08H4.1) that is most identical to the mammalian RhoA-GEF, Tech. Like Tech, T08H4.1 is expressed exclusively in neurons, based on fluorescence from full length
t08h4.1::gfp translational fusions. T08H4.1 dramatically stimulates GTP/GDP exchange on Rho1, but not CED-10 or CDC42. In addition, T08H4.1 stimulates luciferase expression when cotransfected into HEK293 cells with a luciferase reporter under the control of the wild-type serum response element from the c-fos promoter. NIH3T3 cells transfected with a constitutively-active T08H4.1 (T08H4.1C) assume a rounded phenotype. Similarly, the overexpression of T08H4.1C in N1E115 cells causes neurite retraction and cell rounding. Interestingly, T08H4.1 contains a type I PDZ motif (TSDV) at its C-terminus and binds to PDZ domains 8/9 of the multi-PDZ domain scaffold, MPZ-1, in a PDZ motif dependent manner, based on yeast 2-hybrid screening, GST pulldown and co-immunoprecipitation. T08H4.1 and MPZ-1 are co-expressed in a number of neurons and we are currently investigating the effects of this interaction on downstream signaling, neuronal migration and synapse formation in vivo. In addition, we are characterizing other components of the MPZ-1 assembled signaling complexes.