African trypanosomes are parasitic protists which cause endemic disease in sub-Saharan Africa. Both humans and animals can be infected, leading to human or animal African trypanosomiasis (HAT or AAT). These parasites caused several epidemics over the 20th century, in addition to ongoing damage to agriculture on the African continent. Trypanosomes do not invade host cells, and are therefore directly exposed to the mammalian immune system. The evade both innate and adaptive immune responses the parasite has developed a system of antigenic variation, where the surface of the cell is covered in 11 million molecules of a tightly packed coat of variant surface glycoproteins (VSGs). Each cell expresses only one variant surface glycoprotein at a time, and this is periodically switched to evade new antibodies. The process of singular gene expression is termed monoallelic expression and this has two components, establishment and maintenance, i.e. how a single gene is selected for expression and how its singular expression is maintained throughout successive generations.
The establishment of monoallelic VSG gene expression occurs in the salivary gland of the tsetse fly vector. This ensures that the parasite is prepared to infect the next host, as the VSG coat is then prepared to immediately protect the cell. The underlying dynamics of this process are not well understood. We want to deepen our understanding of this process.
Previously, questions such as this were experimentally challenging, as parasites in the salivary gland are mixed populations, limited in number and growth arrested. Recent developments in single cell gene expression profiling have opened new avenues to access difficult questions such as this. Our project aims to use inDrop, a microfluidic droplet based technology to profile the transcriptomes of thousands of single cells as the parasites undergo development in the salivary gland of the fly.
Furthering our understanding of the control of singular VSG gene expression is important in the context of HAT and AAT as this is a key virulence mechanism, without which the parasite cannot establish a new infection. In addition, singular antigen gene expression is a strategy used by other infectious organisms such as malaria and giardia parasites, and this work could be informative in the context of these parasites. More broadly, monoallelic gene expression is a broadly utilized strategy in biological systems, for instance in mammalian olfactory receptors which give us our sense of smell. Further understanding of these processes in a variety of organisms could therefore be informative.
