Abstract
Eukaryotic cilia are microtubule-based organelles that protrude from the cell surface to fulfill sensory and motility functions. Their basic structure consists of an axoneme templated by a centriole/basal body. Striking differences in ciliary ultra-structures can be found at the ciliary base, the axoneme and the tip, not only throughout the eukaryotic tree of life, but within a single organism. Defects in cilia biogenesis and function are at the origin of human ciliopathies. This structural/functional diversity and its relationship with the etiology of these diseases is poorly understood. Some of the important events in cilia function occur at their distal domain, including cilia assembly/disassembly, IFT (intraflagellar transport) complexes’ remodeling, and signal detection/transduction. How axonemal microtubules end at this domain varies with distinct cilia types, originating different tip architectures. Additionally, they show a high degree of dynamic behavior and are able to respond to different stimuli. The existence of microtubule-capping structures (caps) in certain types of cilia contributes to this diversity. It has been proposed that caps play a role in axoneme length control and stabilization, but their roles are still poorly understood. Here, we review the current knowledge on cilia structure diversity with a focus on the cilia distal domain and caps and discuss how they affect cilia structure and function.
Highlights
The Discovery of the Basic Cilia Structure at a GlanceEukaryotic cilia/flagella are fascinating microtubule-based organelles that protrude from the cell surface
Remarks the focus of many studies, the role of the tip membrane domain has been neglected. In this region, A-microtubules are frequently linked to the membrane, but it is expected that receptors and transducers concentrate/organize at this membrane domain
We do not know how specific functions are correlated with a specific cilia tip architectures and the regulation of cellular machineries like the microtubule and actin cytoskeletons
Summary
Eukaryotic cilia/flagella are fascinating microtubule-based organelles that protrude from the cell surface. The diverse group of signaling pathways vertebrates that have been linked todiseases the cilium, from the first work of Pazour et al [37] in to the present, the number of cilia-related makes clear that increased, most function through primary cilia Their diseases loss or encompass dysfunction is has itsignificantly being designated as ciliopathies [48]. This suggests that, in addition to structural and functional cilia diversity, distinct cilia types must have specific proteomes and likely cilia-type specific roles for shared components In support of this idea, Bettencourt-Dias and coworkers [50] have recently described specific localization patterns of 15 evolutionarily conserved ciliary proteins, as for example spindle assembly abnormal protein 6 homolog (SAS6) and centrosomal protein of 290 kDa (CEP290), at the bases of the several neuronal and sperm cilia types of Drosophila melanogaster [50]. In this review we intend to give an overview of the relationship between cilia structural diversity and their functions, focusing mainly on the distal cilia tip domain and ciliary cap structures of different cilia types
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