![]() ![]() White arrow heads point to the empty distal channel. ![]() ( g) Same as (f) except the amphid distal segment is shown. Arrows in the wild-type section point to singlet microtubules that occur less frequently in tbb-4(sa127) mutants. ( f) Electron micrographs of amphid middle segments in wild-type (left), tba-5(qj14) (middle), and tbb-4(sa127) (right) adult animals. See also Figures S3, which shows the ciliary morphology of these mutants in the phasmid and amphids using other markers. Arrows point to transition zones with cilia oriented upward. ( e) Four different markers were used to visualize the phasmid ciliary morphology in the tubulin mutants. ( d) The DYF-1::GFP marker was used to visualize the phasmid ciliary morphology of the double mutants, dyf-6 klp-11, ift-81 klp-11 and ift-74 klp-11, tba-5/klp-11, tbb-4/klp-11, demonstrating that dyf-6, ift-81 and ift-74 are distinct from tba-5(qj14) and tbb-4(tm324). ( b–c) The DYF-1::GFP marker was used to visualize the phasmid ciliary morphology of wild type, three IFT-B mutants (b) and two tubulin mutants (c). ( a) Cartoon illustrating the structure of the phasmid endings. Microscopy and modeling suggests that IFT transport delivers tubulins to the distal tips of axonemal MTs, where they become differentially localized.Ĭharacterization of the dyf-6, ift-81, ift-74, tba-5 and tbb-4 mutants. Here we describe three IFT-B proteins and two tubulin isoforms that are also components of this pathway. Previously, by screening such mutants for defects in the OSM-3/distal segment assembly pathway, we identified the IFT particle subcomplex B (IFT-B) associated protein, DYF-1/IFT70 26, which we propose to be an OSM-3 activator 19, 27. elegans community has produced a valuable collection of mutants that affect IFT and ciliogenesis 25. For example, in vertebrates, heterotrimeric kinesin-2 (KIF3) builds the axoneme core but homodimeric kinesin-2 (KIF17), which is targeted to cilia by the nuclear import machinery, builds distal singlets on zebrafish photoreceptors and targets signaling proteins to primary cilia 2, 23, 24. ![]() Significantly, the hypothesis that IFT moves tubulin subunits along these cilia has not been tested, but the use of two types of kinesin-2 motors to build specific parts of sensory cilia may be widespread. ![]() Subsequently, kinesin-II dissociates from the IFT particles, which are then moved by OSM-3 alone to assemble the distal singlet MTs 19– 22. First, IFT particles, transported by the concerted action of heterotrimeric kinesin-II and homodimeric OSM-3, build the middle segment of the axoneme. In Caenorhabditis elegans, two members of the kinesin-2 family cooperate to drive IFT and assemble sensory cilia on chemosensory neurons. Despite the progress in studying the transport of tubulin along axons 18, the role of IFT in the delivery of tubulin subunits to their site of incorporation within axonemes remains poorly understood 16. tubulin, to the tips of the axoneme 15– 17. IFT-particles are multimeric protein complexes visible by EM as “trains” 13, 14 that are proposed to deliver assembly precursors, e.g. They consist of a specialized ciliary membrane containing signaling molecules surrounding an axoneme that is differentiated longitudinally into a “middle segment” of nine MT doublets, and a “distal segment”, which defines a specialized signaling domain, consisting of nine singlet MTs that extend from the A-tubules of the doublets 2– 6.Ĭilia are assembled by intraflagellar transport (IFT), a process discovered in Chlamydomonas and which involves the kinesin-2 driven movement of IFT particles from the base to the tip of the axoneme 7– 12. Sensory cilia detect and transmit signals that control gene expression, cell behavior and development 1. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |