Characterization of a Cdc42 effector protein (Cep4l) and a novel role for Cdc42 in xenopus neurogenesis and Fgf signaling

The vegetal cortex of the Xenopus oocyte is enriched for several mRNAs critical for early embryonic developmental processes, including germ layer specification and dorsoventral axis formation. A microarray screen for other vegetally localized RNAs identified several hundred annotated and novel cortex-enriched transcripts, in addition to previously known mRNAs, which may have undiscovered roles in early development. Spatiotemporal expression patterns, and overexpression and knockdown phenotypes were analyzed for two novel transcripts, TRIO and F-actin binding protein (TrioBP) and Cdc42 effector protein 4-like (Cep4l). In addition to a maternal role in gastrulation and anteroposterior axis elongation, Cep4l had additional roles in development after zygotic genes become active. Cdc42 is a member of the Rho GTPase family and regulates several cellular processes, including cell division, wound healing, and migration. Activity and role of Cdc42 is dependent on the specific context of activators, inactivators, and downstream interacting effectors. Cep4l bound Cdc42 through its known Cdc42/Rac-interactive binding (CRIB) domain, and that this activation was necessary for Cep4l function. Overexpression of Cep4l after fertilization resulted in pigment distribution defects, reduced anterior structures, and shortened anteroposterior axis. Cep4l also affected Xenopus primary neurogenesis, causing a preferential increase in primary sensory neurons that could be separated from other morphological effects and did not result from major patterning disruption in the neural plate. This increase was shown to come at the expense of neighboring non-neuronal fates, indicating a role for Ceo4l in neural boundary formation. Morpholino (MO) based depletion of Cep4l protein resulted in shortened anteroposterior axis and a requirement for Cep4l in primary neurogenesis that could similarly be separated from gross morphological effects and without effects on neural