Polarity and intracellular compartmentalization of Drosophila neurons

Here we use new and previously characterized markers to examine Drosophila neuronal compartments. We find that: axons and dendrites can accumulate different microtubule-binding proteins; protein synthesis machinery is concentrated in the cell body; pre- and post-synaptic sites localize to distinct regions of the neuron; and specializations similar to the initial segment are present. In addition, we track EB1-GFP dynamics and determine microtubules in axons and dendrites have opposite polarity.We conclude that Drosophila will be a powerful system to study the establishment and maintenance of neuronal compartments.Since individual neurons were first observed, axons and dendrites have been recognized as distinct compartments. Dendrites were proposed to receive information, and axons to transmit it to other sites. Some general morphological features distinguish axons and dendrites. Dendrites are typically shorter than axons, taper as they leave the cell body, and decrease in size as they branch. The diameter of axons is relatively constant, and does not decrease with branching [1]. In the last several decades, molecular differences, including the presence of different membrane and cytoskeletal proteins in neuron subregions, have been added to these original morphological observations [1,2].One type of molecular difference that is likely to be fundamental to neuronal polarity is the distinction between the axonal and dendritic microtubule cytoskeleton. Specific sets of microtubule-binding proteins are found in axons and dendrites. For example, the microtubule-binding protein MAP2 is enriched in dendrites, while dephospho-tau is enriched in axons. The microtubules themselves are also organized differently in axons and dendrites. In axons, microtubules are oriented with their plus-ends distal to the cell body, while in proximal dendrites microtubule polarity is mixed [3]. It is thought that differences in the microtubule cytoskeleton contribute to polarized trafficking to