The Chlamydomonas reinhardtii BBSome is an IFT cargo required for export of specific signaling proteins from flagella

Department of Cell Biology, University of Massachusetts Medical School, Worcester, 01655, USA.
The Journal of Cell Biology (Impact Factor: 9.83). 12/2009; 187(7):1117-32. DOI: 10.1083/jcb.200909183
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In humans, seven evolutionarily conserved genes that cause the cilia-related disorder Bardet-Biedl syndrome (BBS) encode proteins that form a complex termed the BBSome. The function of the BBSome in the cilium is not well understood. We purified a BBSome-like complex from Chlamydomonas reinhardtii flagella and found that it contains at least BBS1, -4, -5, -7, and -8 and undergoes intraflagellar transport (IFT) in association with a subset of IFT particles. C. reinhardtii insertional mutants defective in BBS1, -4, and -7 assemble motile, full-length flagella but lack the ability to phototax. In the bbs4 mutant, the assembly and transport of IFT particles are unaffected, but the flagella abnormally accumulate several signaling proteins that may disrupt phototaxis. We conclude that the BBSome is carried by IFT but is an adapter rather than an integral component of the IFT machinery. C. reinhardtii BBS4 may be required for the export of signaling proteins from the flagellum via IFT.

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Article: The Chlamydomonas reinhardtii BBSome is an IFT cargo required for export of specific signaling proteins from flagella

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    • "ust after cell division genes ( Wood et al . , 2012 ) , we wanted to conduct a comprehensive analysis of basal body and flagella gene expression during the cell cycle . We first curated a core set of 193 basal body and flagella genes ( Basal Body , Axoneme , IFT , and BBsome ) that have been identified in previous studies ( Keller et al . , 2005 ; Lechtreck et al . , 2009 ; Dutcher , 2009 ; Shiratsuchi et al . , 2011 ; Bower et al . , 2013 ) ( Figures 5A to 5C ; Supplemental Data Set 6 ) . Clusters c11 to c14 are significantly enriched for the MapMan ontology term " cell motility " ( z - score > 2 . 5 ) ( Figure 2B ; Supplemental Data Set 3 ) and contain an overrepresentation of known flagella and basal "
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    ABSTRACT: The green alga Chlamydomonas reinhardtii is a useful model organism for investigating diverse biological processes, such as photosynthesis and chloroplast biogenesis, flagella and basal body structure/function, cell growth and division, and many others. We combined a highly synchronous photobioreactor culture system with frequent temporal sampling to characterize genome-wide diurnal gene expression in Chlamydomonas. Over 80% of the measured transcriptome was expressed with strong periodicity, forming 18 major clusters. Genes associated with complex structures and processes, including cell cycle control, flagella and basal bodies, ribosome biogenesis, and energy metabolism, all had distinct signatures of coexpression with strong predictive value for assigning and temporally ordering function. Importantly, the frequent sampling regime allowed us to discern meaningful fine-scale phase differences between and within subgroups of genes and enabled the identification of a transiently expressed cluster of light stress genes. Coexpression was further used both as a data-mining tool to classify and/or validate genes from other data sets related to the cell cycle and to flagella and basal bodies and to assign isoforms of duplicated enzymes to their cognate pathways of central carbon metabolism. Our diurnal coexpression data capture functional relationships established by dozens of prior studies and are a valuable new resource for investigating a variety of biological processes in Chlamydomonas and other eukaryotes.
    The Plant Cell 10/2015; DOI:10.1105/tpc.15.00498 · 9.34 Impact Factor
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    • "These findings raised the question which proteins are the actual cargoes of IFT. Several TRP channels were reported to move by IFT and the BBSome cycles through cilia by associating to IFT trains (Blacque et al., 2004; Qin et al., 2004; Huang et al., 2007; Lechtreck et al., 2009 "
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    ABSTRACT: The assembly of the axoneme, the structural scaffold of cilia and flagella, requires translocation of a vast quantity of tubulin into the growing cilium, but the mechanisms that regulate the targeting, quantity, and timing of tubulin transport are largely unknown. In Chlamydomonas, GFP-tagged α-tubulin enters cilia as an intraflagellar transport (IFT) cargo and by diffusion. IFT-based transport of GFP-tubulin is elevated in growing cilia and IFT trains carry more tubulin. Cells possessing both nongrowing and growing cilia selectively target GFP-tubulin into the latter. The preferential delivery of tubulin boosts the concentration of soluble tubulin in the matrix of growing versus steady-state cilia. Cilia length mutants show abnormal kinetics of tubulin transport. We propose that cells regulate the extent of occupancy of IFT trains by tubulin cargoes. During ciliary growth, IFT concentrates soluble tubulin in cilia and thereby promotes elongation of the axonemal microtubules. © 2015 Craft et al.
    The Journal of Cell Biology 01/2015; 208(2). DOI:10.1083/jcb.201409036 · 9.83 Impact Factor
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    • "Seven BBS gene products (BBS1, BBS2, BBS4, BBS5, BBS7, BBS8, and BBS9) and BBIP10 reside in a stable complex called the BBSome [9,10]. The BBSome interacts with the Rab8 guanine nucleotide exchange factor Rabin8, as well as several other proteins, and mediates trafficking of membrane proteins to and from cilia [9,11,12]. Although numerous proteins have been implicated in vesicular transport to cilia (reviewed in [13]), Rab8 seems to be a key player in the very first stages of ciliary membrane biogenesis. "
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    ABSTRACT: Background Assembly of primary cilia relies on vesicular trafficking towards the cilium base and intraflagellar transport (IFT) between the base and distal tip of the cilium. Recent studies have identified several key regulators of these processes, including Rab GTPases such as Rab8 and Rab11, the Rab8 guanine nucleotide exchange factor Rabin8, and the transport protein particle (TRAPP) components TRAPPC3, -C9, and -C10, which physically interact with each other and function together with Bardet Biedl syndrome (BBS) proteins in ciliary membrane biogenesis. However, despite recent advances, the exact molecular mechanisms by which these proteins interact and target to the basal body to promote ciliogenesis are not fully understood. Results We surveyed the human proteome for novel ASPM, SPD-2, Hydin (ASH) domain-containing proteins. We identified the TRAPP complex subunits TRAPPC8, -9, -10, -11, and -13 as novel ASH domain-containing proteins. In addition to a C-terminal ASH domain region, we predict that the N-terminus of TRAPPC8, -9, -10, and -11, as well as their yeast counterparts, consists of an α-solenoid bearing stretches of multiple tetratricopeptide (TPR) repeats. Immunofluorescence microscopy analysis of cultured mammalian cells revealed that exogenously expressed ASH domains, as well as endogenous TRAPPC8, localize to the centrosome/basal body. Further, depletion of TRAPPC8 impaired ciliogenesis and GFP-Rabin8 centrosome targeting. Conclusions Our results suggest that ASH domains confer targeting to the centrosome and cilia, and that TRAPPC8 has cilia-related functions. Further, we propose that the yeast TRAPPII complex and its mammalian counterpart are evolutionarily related to the bacterial periplasmic trafficking chaperone PapD of the usher pili assembly machinery.
    Cilia 06/2014; 3(1):6. DOI:10.1186/2046-2530-3-6
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