Branching out: mechanisms of dendritic arborization

Abstract

Type-specific dendrite morphology is a hallmark of the neuron and has important functional implications in determining what signals a neuron receives and how these signals are integrated. During the past two decades, studies on dendritic arborization neurons in Drosophila melanogaster have started to identify mechanisms of dendrite morphogenesis that may have broad applicability to vertebrate species. Transcription factors, receptor-ligand interactions, various signalling pathways, local translational machinery, cytoskeletal elements, Golgi outposts and endosomes have been identified as contributors to the organization of dendrites of individual neurons and the placement of these dendrites in the neuronal circuitry. Further insight into these mechanisms will improve our understanding of how the nervous system functions and might help to identify the underlying causes of some neurological and neurodevelopmental disorders.

Figure 1. Mechanisms regulating the formation and organization of dendritic arbors of dendritic arborization neurons in Drosophila melanogaster.

Dendrites of the same neuron spread out by avoiding one another (self-avoidance). Moreover, dendrites of certain types of neurons such as class III and class IV dendritic arborization neurons avoid dendrites of neighbouring neurons of the same type (tiling), whereas dendrites of different neuronal types can cover the same territory (coexistence). Many factors shape the morphology of a dendritc arbor (top panel), including transcription factors, regulators of microtubules and actins (the primary cytoskeletal elements for major dendritic branches and terminal dendritic branches, respectively), Golgi outposts and signalling molecules such as Hippo and Tricornered (TRC) that mediate dendrite–dendrite interactions.

Figure 2. The Hippo pathway coordinates the tiling and maintenance of dendritic fields of Drosophila melanogaster class IV dendritic arborization neurons

The serine–threonine kinase Hippo (HPO) regulates Tricornered (TRC) and Warts (WTS), the only members of the NDR (nuclear DBF2-related) family of kinases in D. melanogaster. TRC and its positive cofactor (Furry) FRY regulate tiling (arrows in the lower right panel indicate dendrite crossover, a tiling defect) whereas WTS and its positive cofactor Salvador (SAV) regulate maintenance. MOB is a shared cofactor. Images are reproduced, with permission, from REF. © (2006). Macmillan Publishers Ltd. All rights reserved.