Distinct Developmental Modes and Lesion-Induced Reactions of Dendrites of Two Classes ofDrosophilaSensory Neurons

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Abstract
Little has been understood about the underlying mechanisms that generate the morphological diversity of dendritic trees. Dendritic arborization neurons in Drosophila provide an excellent model system to tackle this question, and they are classified into classes I–IV in order of increasing arbor complexity. Here we have developed transgenic green fluorescent protein markers for class I or class IV cells, which allowed time-lapse recordings of dendritic birth in the embryo, its maturation processes in the larva, and lesion-induced reactions. The two classes used distinct strategies of dendritic emergence from the cell body and branching, which contributed to differences in their basic arbor patterns. In contrast to the class I cells examined, one cell of class IV, which was a focus in this study, continued to elaborate branches throughout larval stages, and it was much more capable of responding to the severing of branches. We also investigated the cellular basis of field formation between adjacent class IV cells. Our results support the fact that class-specific inhibitory interaction is necessary and sufficient for tiling and confirmed that this intercellular communication was at work at individual dendrodendritic interfaces. Finally, this inhibitory signaling appeared to play a central role when arbors of adjacent cells started meeting midway between the cells and until the body wall became partitioned into abutting, minimal-overlapping territories.