Trypanosoma Cruzi Uses Two Alternative Strategies to Invade Its Host

question 30

Multiple Choice

Trypanosoma cruzi uses two alternative strategies to invade its host cells. To examine the contribution of each of these strategies to the pathogenicity, you culture mammalian cells that can be infected with this pathogen. The cells are engineered to express green fluorescent protein (GFP) fused to a plasma membrane protein, as well as red fluorescent protein (RFP) fused to a lysosome-specific transmembrane protein. You then either add only tiny latex beads (as a negative control) or add T. cruzi protozoa (to infect the cells) . After 10 minutes, you fix the cells and examine them under a fluorescence microscope. You observe that a significant fraction (~30%) of phagosomes/vacuoles in sample 1 are RFP-positive (i.e. show RFP fluorescence at their membrane) , whereas all phagosomes in sample 2 are RFP-negative. Which sample (1 or 2) is the one infected with T. cruzi? In this infected sample, would you expect the RFP-negative trypanosome-containing vacuoles to be GFP-positive or GFP-negative?

• A) Sample 1; GFP-positive
• B) Sample 1; GFP-negative
• C) Sample 2; GFP-positive
• D) Sample 2; GFP-negative

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Definitions:

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