Microbial pathogens use environmental cues to trigger the developmental events needed to infect mammalian hosts or transmit to disease vectors. The parasites causing African sleeping sickness respond to citrate or cis-aconitate (CCA) to initiate life-cycle development when transmitted to their tsetse fly vector. This requires hypersensitization of the parasites to CCA by exposure to low temperature, conditions encountered after tsetse fly feeding at dusk or dawn. Here we identify a carboxylate-transporter family, PAD (proteins associated with differentiation), required for perception of this differentiation signal. Consistent with predictions for the response of trypanosomes to CCA, PAD proteins are expressed on the surface of the transmission-competent ‘stumpy-form’ parasites in the bloodstream, and at least one member is thermoregulated, showing elevated expression and surface access at low temperature. Moreover, RNA-interference-mediated ablation of PAD expression diminishes CCA-induced differentiation and eliminates CCA hypersensitivity under cold-shock conditions. As well as being molecular transducers of the differentiation signal in these parasites, PAD proteins provide the first example of a surface marker able to discriminate the transmission stage of trypanosomes in their mammalian host.
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We thank E. Ullu for the gift of genomic macroarrays, M. Engstler and M. Boshart for the gift of the AnTat1.1 90:13 line, and A. Schneider for pALC14. We thank D. Hall, P. Davies and D. Levin for technical assistance, P. MacGregor for statistical analysis and A. Paterou and D. Murray for Image analysis. This work was supported by a Wellcome Trust project grant and programme grant to K.R.M. S.D. was supported by a BBSRC studentship, a Wellcome Trust Programme Grant to K.R.M. and by a Journal of Cell Science Travelling fellowship for a visit to the laboratory of K.K. Support was also provided through a Wellcome Trust strategic award for the Centre for Immunity, Infection and Evolution and a BBSRC REI award for confocal facilities.
Author Contributions S.D. carried out all trypanosome experiments, R.M. carried out the Xenopus oocyte transport assays, K.K. contributed to the design of the transport assays, and K.R.M. conceived and supervised the study; the manuscript was written by K.R.M. and S.D.
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Dean, S., Marchetti, R., Kirk, K. et al. A surface transporter family conveys the trypanosome differentiation signal. Nature 459, 213–217 (2009). https://doi.org/10.1038/nature07997
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