A New Paradigm for Cell Motility in African Trypanosomes

Trypanosoma brucei is the causative pathogen for the fatal human disease African sleeping sickness. For over 160 years, cellular propulsion in Trypanosoma brucei has been considered to be in an auger-like motion and current understanding of the motility states the cell moves using left-helical waves which propagate along the flagellum. In contrast to the uniform flagellar beats laid out by the traditional model, we find that the frequency was lower at the posterior end compared to the anterior end, suggestive of an alternative and unique mechanism of motility exhibited by Trypanosoma brucei. Our new studies are significant in pioneering a new direction and providing important insight into the actual model of Trypanosma brucei’s movement. As Trypanosome motility is central to disease pathogenesis, parasite development and disease transmission, this investigation provides a requisite step in efforts to exploit cell motility as a target for disease control in African sleeping sickness. Introduction Trypanosoma brucei uses flagellum movement to carry out disease pathogenesis, but the mechanism for carrying this out is not completely elucidated and understood. T. brucei’s flagellum is an essential and critical component for the parasite to carry out cell motility, host-parasite interaction, cell division, and cell morphogenesis (Van Den Abbeele, J., 1999; Vickerman, K., 1988; Hill, K.L., 2003). Efforts to understand trypanosome pathogenesis and fundamental aspects of eukaryotic flagellum are directly related to understanding T. brucei flagellum. The T. brucei development begins in the tsetse fly in what is referred to as a procyclic form. During this procyclic form, the necessity for its motility is particularly acute as the parasite completes a long migration from the midgut of the tsetse fly to the salivary glands. This migration is necessary for the T. brucei to complete its eventual transmission into its mammalian host. Though the path of the parasite’s journey is known, there has yet to be a robust description for how it achieves this transport throughout the insect vector (Hill, K.L., 2003). Upon penetration inside the mammalian host that is achieved by a bite from the infected tsetse fly, the parasite adopts a bloodstream form, invading the central nervous system and rendering the host into a coma and ultimately, death. During all stages of its lifecycle, T. brucei resides extracellularly and thus is completely dependent upon its own cell motility for navigation within the insect vector as well as invasion into the central nervous system of the mammalian host. Such dependency that T. brucei has on its motility emphasizes the importance on studying the mechanism for its movement. For without an efficient method of propagation, the cell could not carry out its pathogenesis. T. brucei is currently a devastating human and animal pathogen that causes significant human mortality and limits sustained economic development in sub-Saharan Africa (Welburn, D., 2002; Sternberg, J.M., 2004). The conventional and present model of the organism’s motility, first described in 1843 (Gruby, D., 1843), assumes continuous auger-like rotation of the entire cell body driven by left helical waves propagating along the flagellum (Hill, K.L., 2003; Walker, P.J., 1961; Kohl, L. and Bastin, P., 2005). In an effort to understand and provide a detailed description of this motion, we performed quantitative analysis of the motility of T. brucei using differentialinterference-contrast (DIC) microscopy. In doing so, we have discovered new information revealing an inconsistency in frequency beats down the cell body and taken numerous recordings of the cell’s motility. Our findings provide important and valuable insight for progress towards targeting the cell motility as a novel means of therapeutic treatment. High-speed imaging to capture and analyze cell motility could be thus applied in efforts to understand other cell’s forms of motion. Materials and Methods Trypanosome cell maintenance and motility assays Procyclic 29-13 and BSF-SM cell lines were used throughout these experiments and maintained as described as follows. Procyclic cells were