Extended Data Fig. 10: Analysis of transferrin receptor expression during growth in sera from different mammals.

a. Sequences of ESAG7 from different transferrin receptor variants within the blood stream expression sites of the Lister 427 strain, showing nucleotide sequences equivalent to 778 to 837 in the BES1 sequence. Below this are shown the predominant sequences found in Trypanosoma brucei cells grown in serum exclusively containing cow, horse, rabbit and pig transferrin for 309 hours. The red lettering and red star indicate a sequence difference at position 798 in which a T is unique to the BES1 receptor. b. Sequencing chromatograms of the expressed transferrin receptor variants in cells, showing nucleotides equivalent to 791 to 805 in the BES1 sequence. The star marks residue 798, which is T in BES1 and C in the other receptors in the Lister 427 strain. The top chromatogram shows that Trypanosoma brucei grown in fetal calf serum (cow) for 72 hours predominantly express BES1. These cells were transferred into media containing serum from cow, pig, horse or rabbit and were grown for a further 119 hours (the 191h time point) and 309 hours (the 381h time point) and the chromatograms show the transferrin receptor sequences expressed at these times remains predominantly BES1, with lower levels of other receptors in all four sera. A similar outcome was seen for ESAG6 sequences (not shown).