In a multitude of life’s processes, eukaryotic cilia and flagella are ubiquitous and indispensable. In the human body, lung and ependymal cilia coordinate the pumping of fluid, but the very same cellular appendages are used by diverse species of protists and algae as microscale analogues of limbs to swim through aqueous environments.
In our group, we focus on evolutionarily ancient microorganisms (e.g. Chlamydomonas, Volvox, Pyramimonas), and use a combination of theory, experiment, and computation to investigate the physics of motile cilia and the mechanistic origins of active cellular motility.
I. Gait-switching and Behavioural Stereotypy
Locomotion, achieved through the actuation of multiple appendages, is inherently combinatorial. Even primitive microorganisms display a fascinating behavioural heterogeneity, transitioning between different swimming modes, or fast and slow dynamics. We use high-resolution spatiotemporal information obtained from quantitative live-cell imaging to characterise stereotyped states or gaits, and estimate gait-switching probabilities, revealing an unprecedented complexity in the non-nervous control of behaviour in single-celled organisms.
Time-irreversibility and criticality in the motility of a flagellate microorganism
K.Y. Wan & R.E. Goldstein, Physical Review Letters 121, 058103 (2018)
Lag, Lock, Sync, Slip: The Many ‘Phases’ of Coupled Flagella
K.Y. Wan, K.C. Leptos & R.E. Goldstein, Journal of the Royal Society Interface 11, 20131160 (2014)
Antiphase Synchronization in a Flagellar-Dominance Mutant of Chlamydomonas
K.C. Leptos*, K.Y. Wan*, M. Polin, I. Tuval, A.I. Pesci & R.E. Goldstein, Physical Review Letters 111, 158101 (2013)
II. Coordination of Eukaryotic Flagella
Cilia and flagella often exhibit synchronized behaviour, including phase-locking and metachronal waves. For several decades, it has been hypothesised that this synchrony arises from fluid dynamical coupling between the nearby filaments. By controlling the distance of separation between pairs of pipette-held somatic cells of Volvox, we proved that hydrodynamic interactions were indeed sufficient to produce synchrony. This does not however, account for all types of ciliary coordination phenomena observed in Nature. We find that unicellular organisms, including Chlamydomonas and Pyramimonas, instead rely upon intracellular coupling through the basal apparatus to orchestrate a few, precisely-oriented, flagella.
Coordinated Beating of Algal Flagella is Mediated by Basal Coupling
K.Y. Wan & R.E. Goldstein, Proceedings of the National Academy of Sciences USA 113, E2784-93 (2016)
Press: Algae use their “tails” to gallop and trot like quadrupeds (Cambridge), Hexadecaflagellates! (freethoughtblogs.com), Great galloping algae (horsetalk.co.nz).
Flagellar Synchronization Through Direct Hydrodynamic Interactions
D.R. Brumley*, K.Y. Wan*, M. Polin & R.E. Goldstein, eLife 3, e02750 (2014)
Press: See accompanying eLife Insight Flagellar beating: row with the flow (B.M. Friedrich & I.H. Riedel-Kruse), Microscopic rowing without a cox (Cambridge).
III. Origins of Biological Stochasticity
Like the human heartbeat, the Chlamydomonas flagellum is a complex biological oscillator, exhibiting strong rhythmicity, yet also responsiveness to certain environmental or physiological cues. Extracting and digitising flagellar beat patterns and frequencies from long-time, high-speed recordings, we devise novel measures of shape and waveform stochasticity and demonstrate the extent to which “the noise is the signal”, correlating changes in flagellar activity with regrowth, hydrodynamic loading, light, or heat shock treatment.
Rhythmicity, Recurrence, and Recovery of Flagellar Beating
K.Y. Wan & R.E. Goldstein, Physical Review Letters 113, 238103 (2014)