Microsporidia are a group of parasites that can only reproduce by invading and taking over an animal cell. They are highly dependent on their host cell for nutrients and energy, which has allowed them to discard genes for many metabolic proteins and evolve unique ways to carry out other essential activities. For example, microsporidian genomes are among the smallest of any complex cell. As the genomes shrink, critical information controlling gene expression has been squeezed from its conventional location. The mitochondria—known as the powerhouse of the cell—is also reduced nearly beyond recognition in form and function. In both these systems, the microsporidia do things differently from other cells, including the host animal cell in which they reside. Dr. Patrick Keeling is studying the effects of a shrunken genome and mitochondria in microsporidia, investigating how these reductions affect the way the parasite expresses its genes and targets proteins for function. Fully understanding these unique characteristics is important because, as with other parasites, such features could be exploited as targets for therapy.