Dendritic morphology constrains microtubule dynamics and organization

Abstract Neuronal dendrites form highly branched morphologies supported by spatially patterned microtubule arrays that are essential for intracellular transport and structural stability, yet how this organization is established and maintained remains unclear. Here we analyze microtubule behavior in Drosophila sensory neurons using live-cell imaging, deep learning–based analysis, and genetic perturbations. We find that microtubules are shorter and fewer in thin distal branches and progressively longer and more abundant in thicker proximal branches. Locally, polymerization slows in narrow branches due to soluble tubulin depletion, while catastrophe frequency increases near branch points upon cortical encounter. A physical model incorporating these morphology-dependent constraints reproduces both local microtubule dynamics and global organization. Inverting the textbook view that microtubule dynamics shape cell morphology, our results demonstrate that, on short timescales, cell morphology instead constrains microtubule dynamics, thereby determining large-scale cytoskeletal organization.