Unraveling the intricate interactions between Trypanosoma brucei, the protozoan parasite causing African trypanosomiasis, and the tsetse (Glossina) vector remains a challenge. Metacyclic trypanosomes, which inhabit the tsetse salivary glands, transmit the disease and are produced through a complex differentiation and unknown program. By overexpressing a single RNA-binding protein, TbRBP6, in cultured noninfectious trypanosomes, we recapitulated the developmental stages that have been observed in tsetse, including the generation of infective metacyclic forms expressing the variant surface glycoprotein. Thus, events leading to acquisition of infectivity in the insect vector are now accessible to laboratory investigation, providing an opening for new intervention strategies.

One distinctive feature of the Trypanosoma brucei life cycle is the presence of two discrete populations that are based on differential expression of variant surface glycoproteins (VSGs). Both are adapted to the environmental pressures they face and more importantly, both contribute directly to transmission. Metacyclics in the tsetse fly enable transmission to a new mammalian host, whereas bloodstream trypanosomes must avoid immune destruction to the extent that sufficient numbers are available for transmission, when the insect vector takes a blood meal. At present, there are few investigations on the molecular aspects of parasite biology in the tsetse vector and specifically about the activation of metacyclic VSG gene expression. Here we used an established in vitro differentiation system based on the overexpression of the RNA-binding protein 6 (RBP6), to monitor two metacyclic VSGs (VSG 397 and VSG 653) during development from procyclics to infectious metacyclic forms. We observed that activation of these two mVSGs was simultaneous both at the transcript and protein level, and manifested by the appearance of only one of the mVSGs in individual cells.