The trypanosome flagellum.

Introduction African Trypanosomes are flagellated protozoan parasites that cause sleeping sickness in humans and Nagana in cattle. During its life cycle, Trypanosoma brucei alternates between an insect vector (tsetse fly) and a mammalian host. Within each of these, the parasite proliferates and undergoes separate periods of differentiation in preparation for each new host/vector environment. The differentiated cell types of the trypanosome life cycle are defined morphologically by the position of the single flagellum, nucleus and kinetoplast (the single mass of mitochondrial DNA). The flagellum is key to these morphological events and hence much attention has focused recently on understanding its role in trypanosome morphogenesis and pathogenicity. However, the tractable cell biology, reverse genetics and advanced genome project mean that the trypanosome is also emerging as an ideal model organism for the studies of eukaryotic flagella and cilia in general. Flagellum functions: morphogenesis to pathogenicity The positioning of the mitochondrial genome in the kinetoplast is a direct consequence of the position and segregation of the flagellum basal bodies (Robinson and Gull, 1991). In addition, the construction of a set of internal cytoskeletal microtubules and filaments are influenced by, and at times defined by, the ontogeny of the external flagellum. Given that these cytoskeletal structures also define three distinct plasma membrane regions (the flagellum membrane, the cell body membrane and the flagellar pocket membrane), the flagellum exhibits a pivotal role in morphogenesis of the trypanosome with many functions beyond those of motility (Gull, 1999). Cell Science at a Glance 757