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.

Download full-text


Available from: Tomer Avidor-Reiss, Nov 12, 2014
131 Reads
  • Source
    • "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). "
    [Show abstract] [Hide abstract]
    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; DOI:10.1016/j.devcel.2015.07.016 · 9.71 Impact Factor
  • Source
    • "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. "
    [Show abstract] [Hide abstract]
    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
  • Source
    • "Comparative, genome-wide analysis of flagellated and non-flagellated organisms has identified several protein datasets associated with flagella or basal bodies (Avidor-Reiss et al. 2004; Judelson et al. 2012; Li et al. 2004). Following the same strategy, we carried out a stringent reciprocal BLAST analysis by comparing CbFP sequences with the genome-encoded proteomes of eighteen selected eukaryotic species to identify putative orthologous proteins of CbFP (Supplementary Material Table S2). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Flagella are conserved organelles among eukaryotes and they are composed of many proteins, which are necessary for flagellar assembly, maintenance and function. Stramenopiles, which include brown algae, diatoms and oomycetes, possess two laterally inserted flagella. The anterior flagellum (AF) extends forward and bears tripartite mastigonemes, whilst the smooth posterior flagellum (PF) often has a paraflagellar body structure. These heterogeneous flagella have served as crucial structures in algal studies especially from a viewpoint of phylogeny. However, the protein compositions of the flagella are still largely unknown. Here we report a LC-MS/MS based proteomics analysis of brown algal flagella. In total, 495 flagellar proteins were identified. Functional annotation of the proteome data revealed that brown algal flagellar proteins were associated with cell motility, signal transduction and various metabolic activities. We separately isolated AF and PF and analyzed their protein compositions. This analysis led to the identification of several AF- and PF-specific proteins. Among the PF-specific proteins, we found a candidate novel blue light receptor protein involved in phototaxis, and named it HELMCHROME because of the steering function of PF. Immunological analysis revealed that this protein was localized along the whole length of the PF and concentrated in the paraflagellar body.
    Protist 09/2014; 165(5). DOI:10.1016/j.protis.2014.07.007 · 3.05 Impact Factor
Show more