title: Social motility of African trypanosomes is a property of a distinct life-cycle stage that occurs early in tsetse fly transmission.
abstract: The protozoan pathogen Trypanosoma brucei is transmitted between mammals by tsetse flies. The first compartment colonised by trypanosomes after a blood meal is the fly midgut lumen. Trypanosomes present in the lumen-designated as early procyclic forms-express the stage-specific surface glycoproteins EP and GPEET procyclin. When the trypanosomes establish a mature infection and colonise the ectoperitrophic space, GPEET is down-regulated, and EP becomes the major surface protein of late procyclic forms. A few years ago, it was discovered that procyclic form trypanosomes exhibit social motility (SoMo) when inoculated on a semi-solid surface. We demonstrate that SoMo is a feature of early procyclic forms, and that late procyclic forms are invariably SoMo-negative. In addition, we show that, apart from GPEET, other markers are differentially expressed in these two life-cycle stages, both in culture and in tsetse flies, indicating that they have different biological properties and should be considered distinct stages of the life cycle. Differentially expressed genes include two closely related adenylate cyclases, both hexokinases and calflagins. These findings link the phenomenon of SoMo in vitro to the parasite forms found during the first 4-7 days of a midgut infection. We postulate that ordered group movement on plates reflects the migration of parasites from the midgut lumen into the ectoperitrophic space within the tsetse fly. Moreover, the process can be uncoupled from colonisation of the salivary glands. Although they are the major surface proteins of procyclic forms, EP and GPEET are not essential for SoMo, nor, as shown previously, are they required for near normal colonisation of the fly midgut.
authors.affiliation: Institute of Cell Biology, University of Bern, Bern, Switzerland; Graduate School of Cellular and Biomedical Sciences, University of Bern, Bern, Switzerland.
authors.forename: Simon
authors.initials: S
authors.lastname: Imhof
authors.affiliation: Institute of Cell Biology, University of Bern, Bern, Switzerland; Graduate School of Cellular and Biomedical Sciences, University of Bern, Bern, Switzerland.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Knüsel
authors.affiliation: Institute of Cell Biology, University of Bern, Bern, Switzerland.
authors.forename: Kapila
authors.initials: K
authors.lastname: Gunasekera
authors.affiliation: Institute of Cell Biology, University of Bern, Bern, Switzerland.
authors.forename: Xuan Lan
authors.initials: XL
authors.lastname: Vu
authors.affiliation: Institute of Cell Biology, University of Bern, Bern, Switzerland.
authors.forename: Isabel
authors.initials: I
authors.lastname: Roditi
mesh_terms: D000818:Animals; D005786:Gene Expression Regulation; D008018:Life Cycle Stages / Q000502:physiology; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D015800:Protozoan Proteins / Q000235:genetics / Q000378:metabolism*; D012469:Salivary Glands / Q000378:metabolism; D014346:Trypanosoma brucei brucei / Q000235:genetics / Q000502:physiology*; D014353:Trypanosomiasis, African / Q000469:parasitology / Q000635:transmission*; D014370:Tsetse Flies / Q000469:parasitology*
chemical_list: C406751:GPEET protein, Trypanosoma brucei; D008562:Membrane Glycoproteins; D015800:Protozoan Proteins