title: The ciliary pocket: an endocytic membrane domain at the base of primary and motile cilia.
abstract: Cilia and flagella are eukaryotic organelles involved in multiple cellular functions. The primary cilium is generally non motile and found in numerous vertebrate cell types where it controls key signalling pathways. Despite a common architecture, ultrastructural data suggest some differences in their organisation. Here, we report the first detailed characterisation of the ciliary pocket, a depression of the plasma membrane in which the primary cilium is rooted. This structure is found at low frequency in kidney epithelial cells (IMCD3) but is associated with virtually all primary cilia in retinal pigment epithelial cells (RPE1). Transmission and scanning electron microscopy, immunofluorescence analysis and videomicroscopy revealed that the ciliary pocket establishes closed links with the actin-based cytoskeleton and that it is enriched in active and dynamic clathrin-coated pits. The existence of the ciliary pocket was confirmed in mouse tissues bearing primary cilia (cumulus), as well as motile cilia and flagella (ependymal cells and spermatids). The ciliary pocket shares striking morphological and functional similarities with the flagellar pocket of Trypanosomatids, a trafficking-specialised membrane domain at the base of the flagellum. Our data therefore highlight the conserved role of membrane trafficking in the vicinity of cilia.
authors.affiliation: Institut Cochin, Université Paris Descartes, CNRS UMR 8104, Paris 75014, France.
authors.forename: Anahi
authors.initials: A
authors.lastname: Molla-Herman
authors.forename: Rania
authors.initials: R
authors.lastname: Ghossoub
authors.forename: Thierry
authors.initials: T
authors.lastname: Blisnick
authors.forename: Alice
authors.initials: A
authors.lastname: Meunier
authors.forename: Catherine
authors.initials: C
authors.lastname: Serres
authors.forename: Flora
authors.initials: F
authors.lastname: Silbermann
authors.forename: Chris
authors.initials: C
authors.lastname: Emmerson
authors.forename: Kelly
authors.initials: K
authors.lastname: Romeo
authors.forename: Pierre
authors.initials: P
authors.lastname: Bourdoncle
authors.forename: Alain
authors.initials: A
authors.lastname: Schmitt
authors.forename: Sophie
authors.initials: S
authors.lastname: Saunier
authors.forename: Nathalie
authors.initials: N
authors.lastname: Spassky
authors.forename: Philippe
authors.initials: P
authors.lastname: Bastin
authors.forename: Alexandre
authors.initials: A
authors.lastname: Benmerah
mesh_terms: D000199:Actins / Q000378:metabolism*; D000818:Animals; D002460:Cell Line; D002465:Cell Movement; D002923:Cilia / Q000378:metabolism* / Q000473:pathology; D003599:Cytoskeleton / Q000378:metabolism*; D004705:Endocytosis; D004848:Epithelium / Q000473:pathology; D005260:Female; D005347:Fibroblasts / Q000473:pathology; D005407:Flagella / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D021962:Membrane Microdomains; D051379:Mice; D008810:Mice, Inbred C57BL; D010060:Ovulation; D015044:Zona Pellucida / Q000378:metabolism
chemical_list: D000199:Actins