Abstract
In the epithelium, Planar Cell Polarity (PCP) signaling coordinates cellular organization along the plane of the tissue, perpendicular to the apicobasal axis. In neurons, polarity is instead expressed through the structural and molecular asymmetry that separates the axon from the somatodendritic compartment. Core PCP proteins are essential for neuronal development and function, and have been linked to neurodevelopmental disorders, including autism spectrum disorders and epilepsy. However, their precise roles in the establishment of neuronal polarity remain incompletely understood.
Here, we identify Dishevelled2 (Dvl2), a central PCP signaling scaffold, as a novel component of the axon initial segment (AIS), the proximal axonal domain that maintains neuronal polarity and initiates action potentials. We show that Dvl2 defines, both in vivo and in cultured hippocampal neurons, a proximal subdomain positioned upstream of the major AIS marker Ankyrin-G (Ank-G) and is closely associated with microtubule bundles. Dvl2 is already detected during early axon specification, suggesting that it participates in the initial organization of the proximal axon. Functional depletion of Dvl proteins disrupts AIS architecture, reduces the accumulation of Ankyrin-G and other core AIS components, and impairs the organization of AIS microtubule bundles. These structural defects translate into altered neuronal excitability, with a reduced AIS-dependent component of the action potential.
Mechanistically, we identify MTCL1 as a microtubule-associated partner that recruits Dvl2 from biomolecular condensate assemblies onto microtubules. This recruitment requires the DIX and PDZ domains of Dvl2. Notably, selective intracellular binders targeting the Dvl2 PDZ domain perturb Dvl2 condensate organization and compromise AIS formation.
Together, our data identify Dvl2 as an organizer of the proximal AIS and reveal a Dvl2-MTCL1-dependent mechanism coupling condensate scaffolding, microtubule organization, and neuronal excitability.