Cell Movement/physiology; Neurons/physiology; Wiskott-Aldrich Syndrome Protein Family/metabolism; rac1 GTP-Binding Protein/metabolism; Angiopoietin-Like Protein 2; Angiopoietin-like Proteins; Angiopoietins/metabolism; Animals; Animals, Newborn; Apoptosis/drug effects; Axons/drug effects; Axons/metabolism; Bromodeoxyuridine/metabolism; Cell Movement/drug effects; Cell Movement/genetics; Cell Proliferation/drug effects; Cells, Cultured; Cerebellum/cytology; Cerebellum/growth & development; Cofilin 1/metabolism; Enzyme Inhibitors/pharmacology; Enzyme-Linked Immunosorbent Assay/methods; Growth Cones/drug effects; Growth Cones/metabolism; Ki-67 Antigen/metabolism; Luminescent Proteins/genetics; Mice; Mice, Knockout; Mutation/genetics; Nerve Tissue Proteins/metabolism; Neurons/drug effects; Organ Culture Techniques/methods; RNA Interference/physiology; RNA, Small Interfering/pharmacology; Transfection/methods; cdc42 GTP-Binding Protein/metabolism; rac1 GTP-Binding Protein/deficiency; rhoA GTP-Binding Protein/metabolism