Golgi outposts locally regulate microtubule orientation in neurons but are not required for the overall polarity of the dendritic cytoskeleton

Microtubule-organizing centers (MTOCs) often play a central role in organizing the cellular microtubule networks that underlie cell function. In neurons, microtubules in axons and dendrites have distinct polarities. Dendrite-specific Golgi outposts, in particular multi-compartment outposts, have emerged as regulators of acentrosomal microtubule growth, raising the question of whether outposts contribute to establishing the overall polarity of the dendritic microtubule cytoskeleton. The cis-Golgi matrix protein GM130 has roles in both the MTOC activity of Golgi and in connecting Golgi compartments to form multi-compartment units. Using a combination of genetic approaches and live imaging in a Drosophila model, we found that GM130 is not essential for the overall polarity of the dendritic microtubule cytoskeleton. However, the mislocalization of multi-compartment Golgi outposts to axons disrupts the uniform orientation of axonal microtubules. This suggests that outposts have the capacity to influence microtubule polarity and, as our data indicate, likely do so independently of microtubule nucleation mediated by the γ-tubulin ring complex (γ-TuRC). Altogether, our results are consistent with the model that multi-compartment Golgi outposts may locally influence microtubule polarity, but that outposts are not necessary for the overall polarity of the dendritic microtubule cytoskeleton.