Cilia and flagella are conserved microtubule-based cell extensions present on most cells in the mammalian body. In addition to their role in cell locomotion and fluid transport, cilia participate in cellular sensing and signaling. Over the past two decades, it has been established that numerous developmental anomalies and diseases are caused by dysfunctional cilia. The goal of our work is to understand how cells assemble and maintain cilia, which both require protein transfer between the cell body and the organelle. A key mechanism that determines the protein content of cilia is intraflagellar transport (IFT), a motor-based motility of large carriers (?IFT trains?) that move proteins in and out of cilia. We will use Chlamydomonas reinhardtii as a unicellular model to determine how IFT identifies proteins destined for the cilium and how the cells regulate the volume and timing of ciliary protein traffic.
In Aim1, we will focus on the transport of tubulin, the main structural protein of cilia and flagella. The amount of tubulin and other axonemal proteins entering cilia on IFT trains is upregulated while cilia grow. Tubulin also enters cilia by diffusion and we will establish the quantitative contribution of each route in cilia assembly. We will determine if IFT54 is part of the previously characterized IFT74-IFT81 tubulin-binding module or if it forms an independent tubulin-binding site. All three proteins interact with tubulin via their tubulin-binding domains (TBDs). Isolated IFT complexes will be used to study if the TBDs undergo biochemical changes related to cargo binding and cilia length. We will attempt to map the TBDs on isolated IFT particles and we will study whether IFT particles undergo structural changes inside cilia potentially explaining the differences in cargo binding. We expect to gain insights into how cells regulate tubulin transport, which is critical for the timing of ciliogenesis and the regulation of ciliary length.
In Aim 2, we will focus on the transport of proteins associated to the ciliary membrane by lipidation. Such proteins are critical for the sensory and signaling functions of cilia. Often, they enter and exit cilia to modulate signaling but the role of IFT in this traffic is mostly unknown. In cilia of C. reinhardtii mutants in BBS proteins or Arl13b, the patterns of membrane-associated proteins are severely affected. In humans, mutations in BBS proteins and Arl13b result in Bardet-Biedl syndrome (BBS) and Joubert syndrome, respectively. Both mutants show loss and abnormal accumulation of membrane-associated proteins in cilia, raising the question whether more than one route of transport is affected. We will use in vivo imaging to determine the role of IFT and diffusion in ciliary entry and export of proteins mislocalized in these mutants. We will test a hypothesis that initial ciliary defects caused directly by the bbs and arl13b mutations will induce additional biochemical defects increasingly impairing cilia over time.

Public Health Relevance

Cilia are thread-like cell extensions present on most cells in the mammalian body. Defects in cilia result in a wide range of developmental defects and diseases ranging from male infertility and chronic airway infections to blindness and obesity. The research proposed here will investigate the mechanisms by which cells establish and maintain the protein composition of cilia to ensure their performance.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
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Nuclear and Cytoplasmic Structure/Function and Dynamics Study Section (NCSD)
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Ainsztein, Alexandra M
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University of Georgia
Schools of Arts and Sciences
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Wingfield, Jenna L; Lechtreck, Karl-Ferdinand; Lorentzen, Esben (2018) Trafficking of ciliary membrane proteins by the intraflagellar transport/BBSome machinery. Essays Biochem 62:753-763
Liu, Peiwei; Lechtreck, Karl F (2018) The Bardet-Biedl syndrome protein complex is an adapter expanding the cargo range of intraflagellar transport trains for ciliary export. Proc Natl Acad Sci U S A 115:E934-E943
Louka, Panagiota; Vasudevan, Krishna Kumar; Guha, Mayukh et al. (2018) Proteins that control the geometry of microtubules at the ends of cilia. J Cell Biol 217:4298-4313
Lechtreck, Karl F; Mengoni, Ilaria; Okivie, Batare et al. (2018) In vivo analyses of radial spoke transport, assembly, repair and maintenance. Cytoskeleton (Hoboken) 75:352-362
Lechtreck, Karl F; Van De Weghe, Julie C; Harris, James Aaron et al. (2017) Protein transport in growing and steady-state cilia. Traffic 18:277-286
Wingfield, Jenna L; Mengoni, Ilaria; Bomberger, Heather et al. (2017) IFT trains in different stages of assembly queue at the ciliary base for consecutive release into the cilium. Elife 6:
Liu, Yi; Visetsouk, Mike; Mynlieff, Michelle et al. (2017) H+- and Na+- elicited rapid changes of the microtubule cytoskeleton in the biflagellated green alga Chlamydomonas. Elife 6:
Snouffer, Ashley; Brown, Desmond; Lee, Hankyu et al. (2017) Cell Cycle-Related Kinase (CCRK) regulates ciliogenesis and Hedgehog signaling in mice. PLoS Genet 13:e1006912
Lechtreck, Karl F (2016) Methods for Studying Movement of Molecules Within Cilia. Methods Mol Biol 1454:83-96
Harris, J Aaron; Liu, Yi; Yang, Pinfen et al. (2016) Single-particle imaging reveals intraflagellar transport-independent transport and accumulation of EB1 in Chlamydomonas flagella. Mol Biol Cell 27:295-307

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