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.

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Trypanosomal phosphodiesterases B1 and B2 (TbrPDEB1 and TbrPDEB2) play an important role in the life cycle of Trypanosoma brucei, the causative parasite of human African trypanosomiasis (HAT), also known as African sleeping sickness. We used homology modeling and docking studies to guide fragment growing into the parasite-specific P-pocket in the enzyme binding site. The resulting catechol pyrazolinones act as potent TbrPDEB1 inhibitors with IC₅₀ values down to 49 nM. The compounds also block parasite proliferation (e.g., VUF13525 (20b): T. brucei rhodesiense IC₅₀ = 60 nM, T. brucei brucei IC₅₀ = 520 nM, T. cruzi = 7.6 μM), inducing a typical multiple nuclei and kinetoplast phenotype without being generally cytotoxic. The mode of action of 20b was investigated with recombinantly engineered trypanosomes expressing a cAMP-sensitive FRET sensor, confirming a dose-response related increase of intracellular cAMP levels in trypanosomes. Our findings further validate the TbrPDEB family as antitrypanosomal target.

Transmission of African trypanosomes by tsetse flies requires that the parasites migrate out of the midgut lumen and colonize the ectoperitrophic space. Early procyclic culture forms correspond to trypanosomes in the lumen; on agarose plates they exhibit social motility, migrating en masse as radial projections from an inoculation site. We show that an Rft1 ؊/؊ mutant needs to reach a greater threshold number before migration begins, and that it forms fewer projections than its wild-type parent. The mutant is also up to 4 times less efficient at establishing midgut infections. Ectopic expression of Rft1 rescues social motility defects and restores the ability to colonize the fly. These results are consistent with social motility reflecting movement to the ectoperitrophic space, implicate N-glycans in the signaling cascades for migration in vivo and in vitro, and provide the first evidence that parasite-parasite interactions determine the success of transmission by the insect host.T setse flies (Glossina spp.) are the definitive hosts of the unicellular parasite Trypanosoma brucei, while a variety of mammals can serve as intermediate hosts. Different subspecies of T. brucei cause sleeping sickness in humans and Nagana in domestic animals. The passage of T. brucei through the tsetse fly was memorably described as a "journey fraught with hazards" (1), because the majority of parasites are either eradicated or fail to complete the life cycle. When trypanosomes are ingested by a tsetse fly as part of a blood meal, bloodstream forms differentiate into early procyclic forms in the midgut lumen. In the first few days of tsetse infection, there are two possible outcomes: the parasites are either purged by the fly or they migrate through/around the peritrophic matrix and colonize the ectoperitrophic space. Extraordinarily little is known about this process: teneral (newly hatched) flies are more susceptible to infection, most probably because the peritrophic membrane is not fully formed and it is easier for parasites to gain access to the ectoperitrophic space (2). There is evidence that several hundred parasites from the initial infectious blood meal are founders of the population in the ectoperitrophic space (3). It is not known, however, if these cross the peritrophic matrix individually or if they migrate in groups. The majority of infections in tsetse do not proceed beyond the midgut stage. Completion of the life cycle involves migration of a small number of parasites to the salivary glands, expansion of the founder population as epimastigote forms, and the production of metacyclic forms that can be transmitted to a new mammalian host (1, 3-5).The different life cycle stages of T. brucei in the fly express characteristic glycosylphosphatidylinositol (GPI)-anchored glycoproteins that are present in several million copies per cell and cover the entire surface. The early procyclic forms, which are detected in the fly midgut for up to 7 days following fly infection (6), are characterized by the presence of the GPI-anchor...

Background: CsTx-1, an ICK motif containing neurotoxin, acts as L-type Ca 2ϩ -channel inhibitor. Results: The partial ␣-helical C terminus of CsTx-1 exhibits cytolytic activity toward prokaryotic and eukaryotic cell membranes. Conclusion: CsTx-1 is one peptide with different domains for ion channel inhibition and cytolytic activity. Significance: Shown is an important new mechanism for the evolution of spider venomous peptides.

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