First, some neurons have morphologically distinct dendrites. Several lines of evidence support the existence of compartments within dendrites. Beyond this basic level of compartmentalization, neurons display extreme diversity in axon and dendrite morphology, and both axons and dendrites contain structurally and functionally distinct subdomains ( Katsuki et al., 2011 Masland, 2004). For example, the microtubule cytoskeleton is organized differently in axons and dendrites, allowing distinct modes of trafficking ( Baas et al., 1988 Horton and Ehlers, 2003). To meet their respective functions, axons and dendrites have distinct morphological and molecular properties. On a basic level, a neuron has two compartments apart from the soma: dendrites, which receive inputs, and axons, which transmit signals. The directional flow of information in the nervous system relies on the compartmentalization of neurons. Thus, Raw defines a potential point of convergence in distinct pathways shaping terminal dendrite patterning. Raw independently influences terminal dendrite elongation through a mechanism that involves modulation of the cytoskeleton, and this pathway is likely to involve the RNA-binding protein Argonaute 1 (AGO1), as raw and AGO1 genetically interact to promote terminal dendrite growth but not adhesion. Consistent with this notion, Raw localizes to branch-points and promotes dendrite stabilization together with the Tricornered (Trc) kinase via effects on cell adhesion. Mutation of one gene, raw, affected multiple aspects of terminal dendrite patterning, suggesting that Raw might coordinate multiple signaling pathways to shape terminal dendrite growth. From this screen, we identified mutations that affected distinct aspects of terminal dendrite development with little or no effect on major dendrite patterning. To identify the developmental bases for compartment-specific patterning in dendrites, we screened for mutations that affect discrete dendritic domains in Drosophila sensory neurons. Axon/dendrite compartmentalization can be attributed to neuronal polarization, but the developmental origin of subcompartments in axons and dendrites is less well understood.
Axons and dendrites likewise contain structurally and functionally distinct subcompartments. The directional flow of information in neurons depends on compartmentalization: dendrites receive inputs whereas axons transmit them.
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