Mitochondrial biogenesis and function in trypanosomes

Trypanosomatids are unicellular parasites that are as devastating in their consequences on health and economy as they are captivating as subjects of biological study. Our research is driven as much by the desire to alleviate the suffering caused by these parasites as by the fascination with the ways they have taken biological principles that underpin all life on earth, and twisted them into something bizarre and unique. This project will study the mitochondrion in the sleeping sickness parasite Trypanosoma brucei. The mitochondrion is a cell organelle that is often described as the 'power plant' of eukaryotic cells (complex cells from multicellular organisms like humans, or unicellular organisms like yeast or trypanosomes that are not bacteria) but we now know that they provide the cell with much more than energy. The trypanosome mitochondrion hosts two particularly bizarre phenomena: a structure called 'kinetoplast' and a process called 'RNA editing'. Mitochondria have their own genome; usually a fairly short, circular piece of DNA. In trypanosomes, however, thousands of circular DNAs form a gigantic network that has been likened to medieval chainmail: the kinetoplast. When a trypanosome divides it has to accomplish faithful duplication of its kinetoplast so that each daughter cell inherits the complete set of genes that is encoded in this genome. Like other mitochondrial genomes, the kinetoplast encodes important proteins that the cell needs to survive. To make these proteins (this is called 'gene expression'), the DNA has first to be transcribed into a messenger molecule, the mRNA. Trypanosomes are unique in that they remodel many of their mitochondrial mRNAs in a very elaborate process called RNA editing. We know from past research in our lab and other labs around the world that maintaining the kinetoplast and expressing its genes is critical for parasite survival. If we interfere with one of these processes, the parasite dies. A main goal of our research is to understand exactly how the cell makes and duplicates its kinetoplast, how it expresses the kinetoplast's genes to make proteins, and what these proteins actually do. This is complicated by the fact that trypanosomes have a complex life cycle. They are transmitted by tsetse flies, and the trypanosome that thrives in the mammalian bloodstream (and makes the mammal sick) changes the purpose of its mitochondrion once it has been taken up by the fly. We have three goals in this project. Our first goal is to identify as many of the proteins that are involved in maintaining and duplicating the kinetoplast, and in expressing its genes, as possible. We and others have identified some of these proteins, but we believe there are many more. Because these processes are so unique there is a good chance that some of these proteins will be unique as well, which makes them potentially very suitable targets for new drugs. These are much needed since current treatment involves drugs that are toxic and drug resistance is emerging in various parts of the world. Our second goal is to understand which of the kinetoplast genes are needed by the parasite when it changes from the mammalian bloodstream form to the one that can survive in the midgut of the tsetse fly. This transformation involves a particular intermediate form, called 'stumpy' because of its peculiar morphology, and the mitochondrial activities in the stumpy form are very poorly understood. Our third goal is to understand how many genes exactly are encoded in the kinetoplast. We know of the ones that encode proteins, but there are many more that are not used to make proteins. Instead, they make small RNA molecules called 'guide RNAs' that are required for the RNA editing process. If we really want to understand how kinetoplast gene expression works we need to know how many guide RNAs there are. And because of advances in DNA sequencing technology we can now for the first time determine this.