Small GTPase Cdc42 is required for multiple aspects of dendritic morphogenesis.

The study of dendritic development in CNS neurons has been hampered by a lack of complex dendritic structures that can be studied in a tractable genetic system. In an effort to develop such a system, we recently characterized the highly complex dendrites of the vertical system (VS) neurons in the Drosophila visual system. Using VS neurons as a model system, we show here using loss-of-function mutations that endogenous Cdc42, a member of Rho family of small GTPases, is required for multiple aspects of dendritic morphogenesis. Cdc42-mutant VS neurons display normal complexity but increased dendritic length compared with wild type and have defects in dendrite caliber and stereotyped dendritic branch positions. Remarkably, Cdc42 mutant neurons also show a 50% reduction in dendritic spine density. These results demonstrate that Cdc42 is a regulator for multiple aspects of dendritic development.