title: Pycnosomes: Condensed Endosomal Structures Secreted by Dictyostelium Amoebae.
abstract: Dictyostelium discoideum has been used largely as a model organism to study the organization and function of the endocytic pathway. Here we describe dense structures present in D. discoideum endocytic compartments, which we named pycnosomes. Pycnosomes are constitutively secreted in the extracellular medium, from which they can be recovered by differential centrifugation. We identified the most abundant protein present in secreted pycnosomes, that we designated SctA. SctA defines a new family of proteins with four members in D. discoideum, and homologous proteins in other protists and eumetazoa. We developed a monoclonal antibody specific for SctA and used it to further characterize secreted and intracellular pycnosomes. Within cells, immunofluorescence as well as electron microscopy identified pycnosomes as SctA-enriched dense structures in the lumen of endocytic compartments. Pycnosomes are occasionally seen in continuity with intra-endosomal membranes, particularly in U18666A-treated cells where intraluminal budding is highly enhanced. While the exact nature, origin and cellular function of pycnosomes remain to be established, this study provides a first description of these structures as well as a characterization of reagents that can be used for further studies.
authors.affiliation: Department of Cell Physiology and Metabolism, Faculty of Medicine, University of Geneva, 1 rue Michel Servet, CH-1211, Geneva 4, Switzerland.
authors.forename: Ayman
authors.initials: A
authors.lastname: Sabra
authors.affiliation: Department of Cell Physiology and Metabolism, Faculty of Medicine, University of Geneva, 1 rue Michel Servet, CH-1211, Geneva 4, Switzerland.
authors.forename: Jade
authors.initials: J
authors.lastname: Leiba
authors.affiliation: Univ. Grenoble Alpes, F-38000 Grenoble, France.|CEA, BIG, Laboratoire Biologie à Grande Echelle, F-38054 Grenoble, France.|INSERM, U1038, F-38054 Grenoble, France.
authors.forename: Lauriane
authors.initials: L
authors.lastname: Mas
authors.affiliation: Univ. Grenoble Alpes, F-38000 Grenoble, France.|CEA, BIG, Laboratoire Biologie à Grande Echelle, F-38054 Grenoble, France.|INSERM, U1038, F-38054 Grenoble, France.
authors.forename: Mathilde
authors.initials: M
authors.lastname: Louwagie
authors.affiliation: Univ. Grenoble Alpes, F-38000 Grenoble, France.|CEA, BIG, Laboratoire Biologie à Grande Echelle, F-38054 Grenoble, France.|INSERM, U1038, F-38054 Grenoble, France.
authors.forename: Yohann
authors.initials: Y
authors.lastname: Couté
authors.affiliation: Univ. Grenoble Alpes, F-38000 Grenoble, France.|CEA, BIG, Laboratoire Biologie à Grande Echelle, F-38054 Grenoble, France.|INSERM, U1038, F-38054 Grenoble, France.
authors.forename: Agnès
authors.initials: A
authors.lastname: Journet
authors.affiliation: Department of Cell Physiology and Metabolism, Faculty of Medicine, University of Geneva, 1 rue Michel Servet, CH-1211, Geneva 4, Switzerland.
authors.forename: Pierre
authors.initials: P
authors.lastname: Cosson
authors.affiliation: Univ. Grenoble Alpes, F-38000 Grenoble, France.|CEA, BIG, Laboratoire Biologie à Grande Echelle, F-38054 Grenoble, France.|INSERM, U1038, F-38054 Grenoble, France.
authors.forename: Laurence
authors.initials: L
authors.lastname: Aubry
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D001692:Biological Transport; D004023:Dictyostelium / Q000276:immunology / Q000378:metabolism* / Q000648:ultrastructure; D004705:Endocytosis; D011992:Endosomes / Q000276:immunology / Q000378:metabolism* / Q000648:ultrastructure; D007425:Intracellular Membranes / Q000378:metabolism; D051379:Mice; D015800:Protozoan Proteins / Q000737:chemistry / Q000235:genetics / Q000276:immunology / Q000378:metabolism
chemical_list: D000911:Antibodies, Monoclonal; D015800:Protozoan Proteins