![]() ![]() In class III and IV da neurons which exhibit more complex dendritic arbors, loss of tutl primarily resulted in a significant decrease in total dendritic length and dendritic field coverage, whereas in class II da neurons, which exhibit simpler dendritic arbors, loss of tutl primarily resulted in a significant decrease in branch number. Loss of function analyses revealed differential and cell autonomous requirements for tutl in mediating aspects of class specific da neuron dendrite morphogenesis. Consistent with previous studies, our analyses revealed expression of Tutl in all da neuron subclasses with localization to cell bodies, dendrites, and axons, however, we further demonstrate differential expression levels of Tutl among da neuron subclasses. Here, we describe novel functional roles for tutl in the development of class specific da neuron dendritic morphologies. RNAi-based studies implicate Dasm1 in mediating dendritic arborization and synapse maturation, , whereas in Dasm1 knockout mice no evident defects in dendrite development or synaptogenesis were observed potentially due to functional redundancy of Dasm1 with the highly related IgSF9b gene. ![]() Analyses of the murine Tutl homolog, Dasm1, have revealed specific expression in the developing hippocampus, however loss of function studies have generated conflicting results. Specifically, tutl was reported to function in dendritic and axonal self-avoidance, and also in proper targeting of axon projections in the CNS. Recent work has identified additional roles for tutl in the specification of axon and dendrite morphology. Previous studies found that tutl is required for bilateral coordinated movement, however no evident defects were observed with respect to CNS morphologies. The Drosophila gene turtle ( tutl) encodes an evolutionarily conserved member of the Tutl/Dasm1/IgSF9 subfamily of IgSF proteins. In addition, several recent studies have demonstrated a requirement of the IgSF member Dscam in mediating dendritic self-avoidance, a form of dendritic tiling, in both Drosophila – and mouse. Moreover, a number of studies have demonstrated roles for the IgSF receptors Robo and Frazzled/Deleted in Colorectal Cancer (DCC) in mediating the development of dendrites in both PNS and CNS neurons in Drosophila –. For example, the receptor Roundabout (Robo) prevents axons from crossing the CNS midline by detecting the soluble ligand Slit, which is secreted by midline cells. IgSF molecules have been directly implicated in regulating both axonal guidance and dendritic arborization. Immunoglobulin superfamily (IgSF) genes encode a large family of evolutionarily conserved proteins that function as cell-adhesion molecules, ligands, and receptors. For example, the class specific distribution of the transcription factors Cut and Knot partially explains the morphological differences observed between class III and class IV da neurons by differentially regulating the actin- and tubulin-based cytoskeleton –. The diversity of da neuron dendritic arbors suggests that each class may have a unique profile of molecules and signaling pathways at work producing the characteristic morphologies. Despite having a similar profile of cell-fate selector genes, these da neurons can be subdivided into four unique morphological classes based on distinct patterns of dendritic arborization. Investigations using da neurons as a model system have revealed a vast array of molecular mechanisms governing class specific dendrite development and dendritic field specification. Although it is known that the spatial distribution of dendritic geometries follows certain well-described principles, the molecular interactions governing dendrite development remain largely unknown.ĭrosophila dendritic arborization (da) neurons provide an exceptional model to study dendrite morphogenesis as they grow elaborate dendritic arbors that occupy a nearly two-dimensional space directly beneath the larval cuticle. Furthermore, the shape of dendrites alters the cable properties of the neuron, providing a mechanism for further modulation of electrochemical signaling. In fact, dendritic arbors have been shown to undergo dynamic remodeling in response to electrochemical signaling, which could represent a morphological correlate of cognitive processes –. As dendrites form the vast majority of the post-synaptic structure, the architecture of dendritic arbors largely determines the synaptic connectivity of neuronal networks. ![]() Neuronal dendrites occur in a staggering array of morphological conformations ranging from short, singular processes to large, highly complex structures. ![]()
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