title: GABAB receptor intracellular trafficking after internalization in Paramecium.
abstract: The number of neurotransmitter receptors on the plasma membrane is regulated by the traffic of intracellular vesicles. Golgi-derived vesicles provide newly synthesized receptors to the cell surface, whereas clathrin-coated vesicles are the initial vehicles for sequestration of surface receptors, which are ultimately degraded or recycled. We have previously shown that GABAB receptors display a punctuate vesicular pattern dispersed on the cell surface and throughout the cytoplasm and are internalized via clathrin-dependent and -independent endocytosis. Here we have studied constitutive GABAB receptor trafficking after internalization in Paramecium primaurelia by confocal laser scanning microscopy and multiple immunofluorescence analysis. After internalization, receptors are targeted to the early endosomes characterized by the molecular markers EEA1 and rab5. Some of these receptors, destined for recycling back to the plasma membrane, traffic from the early endosomes to the endosomal recycling compartment that is characterized by the presence of rab4-immunoreactivity (IR). Receptors that are destined for degradation exit the endosomal pathway at the early endosomes and traffic to the late endosome-lysosome pathway. In fact, some of the GABAB-positive compartments were identified as lysosomal structures by double staining with the lysosomal marker LAMP-1. GABAB vesicle structures also colocalize with TGN38-IR and rab11-IR. TGN38 and rab11 are proteins found in association with post-Golgi and recycling endosomes, respectively.
authors.affiliation: Department for the Study of Territory and its Resources (DIP.TE.RIS.), University of Genoa, 16132 Genoa, Italy. ramoino@dipteris.unige.it
authors.forename: Paola
authors.initials: P
authors.lastname: Ramoino
authors.forename: Cesare
authors.initials: C
authors.lastname: Usai
authors.forename: Francesco
authors.initials: F
authors.lastname: Beltrame
authors.forename: Marco
authors.initials: M
authors.lastname: Fato
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Gallus
authors.forename: Grazia
authors.initials: G
authors.lastname: Tagliafierro
authors.forename: Raffaella
authors.initials: R
authors.lastname: Magrassi
authors.forename: Alberto
authors.initials: A
authors.lastname: Diaspro
mesh_terms: D000818:Animals; D011992:Endosomes / Q000378:metabolism; D005455:Fluorescent Antibody Technique / Q000379:methods; D007091:Image Processing, Computer-Assisted; D008247:Lysosomes / Q000378:metabolism; D018613:Microscopy, Confocal / Q000379:methods; D010247:Paramecium / Q000378:metabolism*; D018080:Receptors, GABA-B / Q000378:metabolism*; D020691:rab GTP-Binding Proteins / Q000378:metabolism
chemical_list: D018080:Receptors, GABA-B; D020691:rab GTP-Binding Proteins