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Neuron dendrite1/9/2024 ![]() For instance, the dendritic arbors of retinal ganglion cells (RGCs) are easily distinguishable from those of amacrine cells, and the difference between dendrites of Purkinje cells and granule neurons in the cerebellum is even more dramatic ( Figure 1). However, studies in the retina offer a glimpse of the enormous diversity of dendritic branching patterns. Comprehensive experimental categorization of all neurons seems to be a task as daunting as the current effort to document all species on the planet. ![]() Based on some reasonable assumptions, thousands of neuronal types are probably present in primate cortex. Therefore, the diversity of dendritic morphology closely correlates with the number of neuronal types. The size and shape of dendritic arbors are major defining characteristics of neurons. Instead, I will focus on transcriptional control, role of membrane protein trafficking, dendritic targeting and self-recognition and highlight some exciting new progresses mostly in Drosophila and challenges ahead. In this review, it is impossible to cover all recent relevant studies, such as dendritic maintenance, spine formation or regulation by neuronal activity. The application of genetic approaches to identifiable central or peripheral neurons in intact animals, especially Drosophila, has provided mechanistic insights into dendritic outgrowth and branching, dendritic targeting, and self-recognition. Cell culture and in vivo imaging approaches are instrumental in revealing the roles of a number of extrinsic and intrinsic regulators of this process. Yet, the molecular logics underlying dendritic morphogenesis still remains largely undefined. As appreciated by Ramón y Cajal a century ago, examining the morphological features of neurons is essential for our understanding of the whole nervous system. Neurons distinguish themselves from other cell types partly by their size and shape, especially their unique and often highly branched dendritic trees that remain relatively stable up to decades. Those exciting findings have enhanced significantly our understanding of dendritic morphogenesis and revealed the magnitude of complexity in the underlying molecular regulatory networks. However, the dendrites of a neuron do not cross over each other, a process called self-avoidance that is mediated by Down’s syndrome cell adhesion molecule (Dscam). ![]() Nonredundant coverage by dendrites of same type of neurons, known as tiling, requires the actions of the Tricornered/Furry (Sax-1/Sax-2) signaling pathway. In addition to other intrinsic molecular pathways such as membrane protein trafficking, interactions between neighboring dendritic branches also contribute to the final specification of dendritic morphology. Recent evidence indicates that highly complex transcriptional regulatory networks dictate various aspects of dendritic outgrowth, branching, and routing. Dendrites exhibit unique cell-type specific branching patterns and targeting specificity that are critically important for neuronal function and connectivity.
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