PlexinA3 Interacts with CRMP2 to Mediate Sema3A Signalling During Dendritic Growth in Cultured Cerebellar Granule Neurons.

Plexin family proteins mediate semaphorin signalling during dendritic arbour development. However, the role of PlexinA3 in the growth of dendrites of cultured cerebellar granule neurons (CGNs) is not known. We found that PlexinA3 colocalizes with CRMP2 (collapsin response mediator protein 2) in dendritic shafts. Immunoprecipitation and glutathione transferase pulldown assays showed that the intracellular Ras-binding domain of PlexinA3 directly interacts with CRMP2. PlexinA3 was necessary and sufficient for the growth of CGN dendrites, as genetic knockdown of PlexinA3 reduced but its overexpression increased dendritic lengths and dendritic tip numbers. These increases were enhanced with CRMP2 overexpression and abolished with CRMP2 knockdown, indicating that CRMP2 is the downstream effector. Furthermore, PlexinA3/CRMP2 signalling contributed to Sema3A-controlled dendritic growth. Together, these data identify a novel PlexinA3/CRMP2 pathway in semaphorin-regulated growth of cultured CGN dendrites.