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Cell differentiation in Trypanosoma brucei is a bistable developmental switch requiring new protein synthesis to achieve signal memory

ABSTRACT: The life cycle of Trypanosoma brucei involves several cell differentiation transitions that allow transmission, survival and proliferation of these parasites. One of these transitions, the differentiation of growth-arrested stumpy forms in the mammalian blood into proliferating insect-stage procyclic forms, can be induced synchronously in vitro by addition of cis-aconitate (CA). Using single-cell analysis by flow-cytometry to follow differentiation, we show that this transition is an irreversible bistable switch where cells commit to differentiation after 1-3 hours of exposure to CA. This irreversibility implies the existence of positive feedback mechanisms that allow commitment to differentiation: i.e. the establishment of “memory” of exposure to the differentiation signal. Such mechanisms probably depend on post-translational modifications (e.g. phosphorylation) and/or synthesis of regulatory proteins. Using the reversible protein synthesis inhibitor cycloheximide, we find that protein synthesis is required for establishment of signal memory and normal commitment to differentiation. To characterize the ‘commitment proteome’, we performed SILAC phosphoproteomics to provide a detailed map of the protein expression and phosphorylation events during the early stages of differentiation in a synchronised parasite population. Using a rigorous candidate gene approach we have also demonstrated that the stumpy form enriched serine-throenine protein kinases TbNRKA/B stringently control the earliest events in differentiation identifying these kinases as major regulators of trypanosome development.

INSTRUMENT(S):

ORGANISM(S): Trypanosoma Brucei

DISEASE(S): Trypanosomiasis

SUBMITTER: Michael Urbaniak