Discussion

The African trypanosome undergoes density-dependent differentiation in the mammalian bloodstream to prepare for transmission by tsetse flies. This involves the generation of cell-cycle arrested, quiescent, stumpy forms from proliferative slender forms. The signalling pathway responsible for the quorum sensing response was catalogued using a genome wide selective screen, providing a compendium of signalling kinases phosphatases, RNA binding proteins and hypothetical proteins (Mony et al, Nature, 505, 681&hypen;685; 2014). However, the ordering of these components is unknown, as is the surface receptor that initiates the signalling response and the action of the effectors that drive changes in gene expression once the signal is received. Since our description of the signalling pathway, our lab has been intensively involved in piecing together all of these components to provide comprehensive description of how stumpy formation arises. In particular, using a combination of several distinct genome-wide RNAi screens, combinatorial gene knockout and overexpression analyses, as well as functional analyses of a surface transporter protein and gene regulators we have dissected how stumpy form transcripts are repressed in slender forms, and the dependency-relationships between components in the signalling pathway with respect to one another. The integration of these different approaches to understand stumpy formation is providing the first detailed picture of the structure and interactions in a signalling pathway in trypanosomes.