Decoding cilia function. Defining specialized genes required for compartmentalized cilia biogenesis

Howard Hughes Medical Institute and Division of Biological Sciences and Department of Neurosciences, University of California at San Diego, La Jolla, CA 92093, USA.
Cell (Impact Factor: 32.24). 06/2004; 117(4):527-39.
Source: PubMed


The evolution of the ancestral eukaryotic flagellum is an example of a cellular organelle that became dispensable in some modern eukaryotes while remaining an essential motile and sensory apparatus in others. To help define the repertoire of specialized proteins needed for the formation and function of cilia, we used comparative genomics to analyze the genomes of organisms with prototypical cilia, modified cilia, or no cilia and identified approximately 200 genes that are absent in the genomes of nonciliated eukaryotes but are conserved in ciliated organisms. Importantly, over 80% of the known ancestral proteins involved in cilia function are included in this small collection. Using Drosophila as a model system, we then characterized a novel family of proteins (OSEGs: outer segment) essential for ciliogenesis. We show that osegs encode components of a specialized transport pathway unique to the cilia compartment and are related to prototypical intracellular transport proteins.

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Available from: Tomer Avidor-Reiss, Nov 12, 2014
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    • "In contrast to the importance of IFT for the assembly of cilia in most somatic tissues, Plasmodium falciparum has flagellated gametes yet lacks IFT genes. In this species, it is thought that axonemal assembly occurs in the cytoplasm and the axoneme does not become membrane enclosed until after assembly (Avidor-Reiss et al., 2004). Although IFT is needed for assembly of sensory cilia in D. melanogaster, it is dispensable for sperm flagellar assembly in this organism also. "
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    ABSTRACT: Drosophila sperm are unusual in that they do not require the intraflagellar transport (IFT) system for assembly of their flagella. In mouse, we find that the IFT proteins are very abundant in testis but mature sperm are completely devoid of them, making the importance of IFT to mammalian sperm development unclear. To address this question, we characterized spermiogenesis and fertility in the Ift88(Tg737Rpw) mouse. This mouse has a hypomorphic mutation in the gene encoding the IFT88 subunit of the IFT particle. This mutation is highly disruptive to ciliary assembly in other organs. Ift88(-/-) mice are completely sterile. They produce ∼350-fold fewer sperm than wild-type mice and the remaining sperm completely lack or have very short flagella. The short flagella rarely have axonemes but assemble ectopic microtubules and outer dense fibers, and accumulate improperly assembled fibrous sheath proteins. Thus, IFT is essential for the formation but not the maintenance of mammalian sperm flagella.
    Molecular biology of the cell 10/2015; DOI:10.1091/mbc.E15-08-0578 · 4.47 Impact Factor
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    • "Strikingly, KD of the peripheral protein IFT43 displayed a strong phenotype, and that of IFT144 did not seem to disrupt any signaling pathway tested (Figure S2). To measure the extent of IFT144 KD, and to confirm that the lack of signaling phenotypes is not due to inefficient KD, we analyzed two GFP-tagged expression constructs: IFT144-GFP and, for comparison, IFT121-GFP (Avidor-Reiss et al., 2004) (IFT121 KD served as the control, because it displayed a Wg-signaling defect-like phenotype). RNAi targeting of both genes reduced their protein expression to barely detectable levels, indicating that IFT144 was efficiently silenced, similar to IFT121 (Figure S2S). "
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    ABSTRACT: The development of multicellular organisms requires the precisely coordinated regulation of an evolutionarily conserved group of signaling pathways. Temporal and spatial control of these signaling cascades is achieved through networks of regulatory proteins, segregation of pathway components in specific subcellular compartments, or both. In vertebrates, dysregulation of primary cilia function has been strongly linked to developmental signaling defects, yet it remains unclear whether cilia sequester pathway components to regulate their activation or cilia-associated proteins directly modulate developmental signaling events. To elucidate this question, we conducted an RNAi-based screen in Drosophila non-ciliated cells to test for cilium-independent loss-of-function phenotypes of ciliary proteins in developmental signaling pathways. Our results show no effect on Hedgehog signaling. In contrast, our screen identified several cilia-associated proteins as functioning in canonical Wnt signaling. Further characterization of specific components of Intraflagellar Transport complex A uncovered a cilia-independent function in potentiating Wnt signals by promoting β-catenin/Armadillo activity.
    Developmental Cell 09/2015; 34(6). DOI:10.1016/j.devcel.2015.07.016 · 9.71 Impact Factor
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    • "In addition, the cell bodies of those sensory neurons that lack dendrites are often clustered together (Figure 1F). The mechanosensory organ defects displayed by mecA 101 are more severe than those observed in mutations that specifically affect components of the sensory cilium; in such mutations the dendrite extends to the base of the socket, and absence or clustering of neuronal cell bodies is not observed (Avidor-Reiss et al. 2004; Blachon et al. 2008; Basiri et al. 2014). However, the mecA phenotype resembles that of nompA, which also often fails to innervate the bristle base. "
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    ABSTRACT: The dendrite of the sensory neuron is surrounded by support cells and is composed of two specialized compartments: the inner segment and the sensory cilium. How the sensory dendrite is formed and maintained is not well understood. Hook-related proteins (HkRP) like Girdin, DAPLE, and Gipie are actin-binding proteins, implicated in actin organization and in cell motility. Here, we show that the Drosophila melanogaster single member of the Hook-related protein family, Girdin, is essential for sensory dendrite formation and function. Mutations in girdin were identified during a screen for fly mutants with no mechanosensory function. Physiological, morphological, and ultra-structural studies of girdin mutant flies indicate that the mechanosensory neurons innervating external sensory organs (bristles) initially form a ciliated dendrite that degenerates shortly after, followed by the clustering of their cell bodies. Importantly, we observed that Girdin is expressed transiently during dendrite morphogenesis in three previously unidentified actin-based structures surrounding the inner segment tip and the sensory cilium. These actin structures are largely missing in girdin. Defects in cilia are observed in other sensory organs such as those mediating olfaction and taste, suggesting that Girdin has a general role in forming sensory dendrites in Drosophila. These suggest that Girdin functions temporarily within the sensory organ and that this function is essential for the formation of the sensory dendrites via actin structures. Copyright © 2015, The Genetics Society of America.
    Genetics 06/2015; DOI:10.1534/genetics.115.178954 · 5.96 Impact Factor
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