title: Procyclin gene expression and loss of the variant surface glycoprotein during differentiation of Trypanosoma brucei.
abstract: In the mammalian host, the unicellular flagellate Trypanosoma brucei is covered by a dense surface coat that consists of a single species of macromolecule, the membrane form of the variant surface glycoprotein (mfVSG). After uptake by the insect vector, the tsetse fly, bloodstream-form trypanosomes differentiate to procyclic forms in the fly midgut. Differentiation is characterized by the loss of the mfVSG coat and the acquisition of a new surface glycoprotein, procyclin. In this study, the change in surface glycoprotein composition during differentiation was investigated in vitro. After triggering differentiation, a rapid increase in procyclin-specific mRNA was observed. In contrast, there was a lag of several hours before procyclin could be detected. Procyclin was incorporated and uniformly distributed in the surface coat. The VSG coat was subsequently shed. For a single cell, it took 12-16 h to express a maximum level of procyclin at the surface while the loss of the VSG coat required approximately 4 h. The data are discussed in terms of the possible molecular arrangement of mfVSG and procyclin at the cell surface. Molecular modeling data suggest that a (Asp-Pro)2 (Glu-Pro)22-29 repeat in procyclin assumes a cylindrical shape 14-18 nm in length and 0.9 nm in diameter. This extended shape would enable procyclin to interdigitate between the mfVSG molecules during differentiation, exposing epitopes beyond the 12-15-nm-thick VSG coat.
authors.affiliation: Max-Planck-Institut für Biologie, Tübingen, Federal Republic of Germany.
authors.forename: I
authors.initials: I
authors.lastname: Roditi
authors.forename: H
authors.initials: H
authors.lastname: Schwarz
authors.forename: T W
authors.initials: TW
authors.lastname: Pearson
authors.forename: R P
authors.initials: RP
authors.lastname: Beecroft
authors.forename: M K
authors.initials: MK
authors.lastname: Liu
authors.forename: J P
authors.initials: JP
authors.lastname: Richardson
authors.forename: H J
authors.initials: HJ
authors.lastname: Bühring
authors.forename: J
authors.initials: J
authors.lastname: Pleiss
authors.forename: R
authors.initials: R
authors.lastname: Bülow
authors.forename: R O
authors.initials: RO
authors.lastname: Williams
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002454:Cell Differentiation; D015342:DNA Probes; D004591:Electrophoresis, Polyacrylamide Gel; D005434:Flow Cytometry; D005455:Fluorescent Antibody Technique; D005786:Gene Expression Regulation; D007700:Kinetics; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D015394:Molecular Structure; D009693:Nucleic Acid Hybridization; D011487:Protein Conformation; D012333:RNA, Messenger / Q000096:biosynthesis; D014346:Trypanosoma brucei brucei / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D014643:Variant Surface Glycoproteins, Trypanosoma / Q000378:metabolism*
chemical_list: D015342:DNA Probes; D012333:RNA, Messenger; D014643:Variant Surface Glycoproteins, Trypanosoma