Three-Dimensional Dynamics of a Eukaryotic Flagellum Revealed by High-Speed Holographic Microscopy

Abstract

Understanding the mechanics of the eukaryotic flagellum is a key challenge in biophysics. As well as being of scientific interest, there are clear therapeutic applications, not least in reproductive medicine. The physics of swimming sperm has been studied for some time and there are several competing hypotheses for the underlying mechanics of the axoneme. A key aspect of this work remains unaddressed, however: almost all flagellar waveforms are three-dimensional. Comparing 2D theories with 2D images has met with some success, but for a complete understanding, the 3D nature of the beating must be considered. We have employed digital holographic microscopy to record the 3D beating of a gamete of Plasmodium berghei (a parasite associated with malaria in rodents). When coupled with high-speed imaging we are able to obtain a complete record of the flagellar waveform with excellent temporal and spatial resolution. This sperm is an interesting limiting case: it has no head, and almost no other accessory structures. Our analysis of the 3D beating pattern has implications for the proposed link between structural chirality in the axoneme and the chirality of flagellar waveforms.View Large Image | View Hi-Res Image | Download PowerPoint Slide