Abstract
Knowing when and where a given protein is activated within intact animals assists in elucidating its
in vivo
function. Using genetically encoded A-probe (
a
ctivation bio
probe
), we reveal that Cdc42 GTPase remains inactive within
Drosophila
embryos during the first two-thirds of embryogenesis. Within the central nervous system where Cdc42 activity first becomes upregulated, individual neurons display patterns restricted to specific subcellular compartments. At both the organismal and cellular levels, Cdc42's endogenous activation patterns in wild type allow predictions of where loss-of-function phenotypes will emerge in
cdc42/cdc42
mutants. Genetic tests support the importance of suppressing endogenous Cdc42 activities until needed. Thus, bioprobe-assisted analysis uncovers how a ubiquitously expressed signaling protein controls normal cellular events through continual regulation of its activity within animals.
