Bioelectric control of locomotor gaits in the walking ciliate Euplotes

Biased Lévy Walk Enables Light Gradient Sensing in Euglena gracilis

We examine the navigation behavior of the photosensitive alga Euglena gracilis in confined environments. Under uniform lighting conditions, E. gracilis exhibits stochastic movements with nearly straight runs interrupted by abrupt directional changes. The lengths of these runs follow a long-tailed distribution typical of a Lévy walk, with scaling exponents that vary with light intensity. In gradient lighting conditions, the cells modulate their run durations-extending them upon detecting an increase in light intensity and shortening them when a decrease is detected. This adjustment effectively biases the Lévy walk, enabling the cells to ascend the spatial light gradient. This behavior mirrors well-known prokaryotic stochastic navigation strategies, such as bacterial chemotaxis, offering a eukaryotic parallel. The experimental observations under varied lighting conditions are consistently replicated through an agent-based model.

Inwardly rectifying potassium channels regulate membrane potential polarization and direction sensing during neutrophil chemotaxis

Potassium channels regulate membrane potential and diverse physiological processes, including cell migration. However, the specific function of the inwardly rectifying potassium channels in immune cell chemotaxis is unknown. Here, we identified that the inwardly rectifying potassium channel Kir7.1 (KCNJ13) maintains the resting membrane potential and is required for directional sensing during neutrophil chemotaxis. Pharmacological or genetic inhibition of Kir7.1 in neutrophils impaired direction sensing toward various chemoattractants without affecting cell polarization in multiple neutrophil models. Using genetically encoded voltage indicators, we observed oscillating depolarization of the membrane potential in protrusions in zebrafish neutrophils, and Kir7.1 is required for polarized depolarization towards the chemokine source. Focal depolarization with optogenetic tools biases pseudopod selection and induces de novo protrusions. Global hyperpolarizing neutrophils stalled cell migration. Furthermore, Kir7.1 regulates GPCR signaling activation. This work adds membrane potential to the intricate feedforward mechanism, coupling the adaptive and excitable network required to steer immune cells in complex tissue environments.

Electrical signaling and coordinated behavior in the closest relative of animals

The transition from simple to complex multicellularity involves division of labor and specialization of cell types. In animals, complex sensory-motor systems are primarily built around specialized cells of muscles and neurons, though the evolutionary origins of these and their integration remain unclear. Here, to investigate sensory-behavior coupling in the closest relatives of animals, we established a line of the choanoflagellate, Salpingoeca rosetta, which stably expresses the calcium indicator RGECO1. Using this, we identify a previously unknown cellular behavior associated with electrical signaling, in which ciliary arrest is coupled with apical-basal contraction of the cell. This behavior and the associated calcium transients are synchronized in the multicellular state and result in coordinated ciliary arrest and colony-wide contraction, suggesting that information is spread among the cells. Our work reveals fundamental insights into how choanoflagellates sense and respond to their environment and enhances our understanding of the integration of cellular and organism-wide behavior in the closest protistan relatives of animals.

Biophysics of protist behaviour

Protists, an umbrella term first coined by Ernst Haeckel in 1866, are a vast collection of (primarily unicellular) eukaryotes that are "neither animals nor plants". This basic definition by exclusion has been exercised for centuries, even though recent advances have led to more rigorous taxonomic assignment of various protist groups. Pioneering comparative phylogenetic approaches have been applied to these organisms to reconstruct the deep branches of the eukaryotic tree, revealing essential clues about early eukaryotic evolution. Protists, including amoebae, flagellates, ciliates, and algae, are also vital constituents of global ecosystems, where they appear at the base of food chains, control the relative abundance of other microbes, and participate in global biogeochemical recycling. Due to their typically small size and lack of nervous systems, protists are often associated with the unfortunate label 'primitive'. Yet they exhibit remarkable behavioural sophistication and are able to feed, predate, navigate and interact with their surroundings. Unlike macroscopic animals, many protists reside in a non-intuitive physical regime where viscous forces dominate over inertia, and where they use diverse propulsion and navigation strategies. Interdisciplinary research into these cell-scale phenomena, characterised by a complex interplay of physical forces and mechanical constraints, has significantly advanced the emerging fields of active matter, microhydrodynamics, and non-equilibrium statistical physics. This primer discusses the biophysics of protist behaviour, with a focus on locomotion and feeding. I will highlight the most extensively studied principles and describe some more esoteric behaviours that have not yet been systematically explored.

A QR Code for the Brain: A dynamical systems framework for computing neurophysiological biomarkers

Neural circuits are often considered the bridge connecting genetic causes and behavior. Whereas prenatal neural circuits are believed to be derived from a combination of genetic and intrinsic activity, postnatal circuits are largely influenced by exogenous activity and experience. A dynamical neuroelectric field maintained by neural activity is proposed as the fundamental information processing substrate of cognitive function. Time series measurements of the neuroelectric field can be collected by scalp sensors and used to mathematically quantify the essential dynamical features of the neuroelectric field by constructing a digital twin of the dynamical system phase space. The multiscale nonlinear values that result can be organized into tensor data structures, from which latent features can be extracted using tensor factorization. These latent features can be mapped to behavioral constructs to derive digital biomarkers. This computational framework provides a robust method for incorporating neurodynamical measures into neuropsychiatric biomarker discovery.

Cell motility: Bioelectrical control of behavior without neurons

Single cells are capable of remarkably sophisticated, sometimes animal-like, behaviors. New work demonstrates bioelectric control of motility through the differential regulation of appendage movements in a unicellular organism that walks across surfaces using leg-like bundles of cilia.