Cilium-specific protein required to control the microtubule-based, ciliary axoneme structure. May act by maintaining the association between IFT subcomplexes A and B. Binds GTP but is not able to hydrolyze it; the GTPase activity remains unclear. Required to pattern the neural tube. Involved in cerebral cortex development: required for the initial formation of a polarized radial glial scaffold, the first step in the construction of the cerebral cortex, by regulating ciliary signaling (PubMed:23817546). Regulates the migration and placement of postmitotic interneurons in the developing cerebral cortex (PubMed:23153492). Monomer. Interacts with IFT complex B components IFT46 and IFT74 (By similarity). Interacts with PIFO (By similarity) (PubMed:20643351). Interacts with EXOC2; regulates ARL13B localization to the cilium membrane (PubMed:26582389). Associates to the cilium membrane via palmitoylation. Localizes to proximal ciliary membranes, to an inversin-like subciliary membrane compartment, excluding the transition zone. Cilium-specific protein. Expressed in neuroepithelial cells and developing radial glia of the developing cerebral cortex: present in both neuroepithelial and radial progenitor cells. In radial progenitors, found in the apical, cell soma domains of these cells (at protein level). Expressed in the primary cilia of postmitotic cortical neurons during embryonic and postnatal development. Sumoylation is required for PKD2 entry into cilium. Impaired cilium's ability to convey critical extracellular signals such as Shh, without destroying cilia and their downstream pathways. Mice show a constitutive low-level of Shh activity owing to loss of modulation of Gli2 activator, corresponding to the specification of progenitors of motoneurons through most of the neural tube. In contrast to other mouse mutants that disrupt cilia, Gli3 repressor activity is unaffected in mutants (PubMed:17488627). Mutants show abnormal cilia in which components of Shh signaling are not regulated properly: Ptch1 and Smo localize to cilia regardless of Shh stimulation, and there is no Gli enrichment in cilia upon Shh stimulation (PubMed:21976698). Conditional deletion disrupts interneuronal placement, but not postmigratory differentiation in the developing cerebral cortex (PubMed:23153492). Early neuroepithelial-specific deletion in cortical progenitors induces a reversal of the apical-basal polarity of radial progenitors and aberrant neuronal placement (PubMed:23817546). Used as a ciliary marker because of its specific localization to microtubule doublets of the ciliary axoneme. Frequently used to study cilium signaling, since in contrast to most cilia null mutants, deletion of Arl13b impairs without destroying cilia and their downstream pathways (PubMed:23817546). Belongs to the small GTPase superfamily. Arf family.