Biology subjects

Usherwood, T. R.

Publications and source records attributed to Usherwood, T. R..

4 recordsLinked to original sources

bioRxiv2025

Inertial sensing of water content in tumor spheroids

Cellular water content governs the concentration of all biomolecules inside a cell, thereby influencing the physical and functional properties of the cell. However, measurements of water content in physiologically relevant cell culture models remain largely unavailable, particularly in 3D models such as tumor spheroids and organoids. Here, we achieve such measurements using a commercially available, industrial-grade, steel tube. The steel tube functions as a mechanical resonator that inertially senses the buoyant mass of particles. For microgram-scale particles [≥]400 {micro}m in diameter, we achieve <1% precision error in buoyant mass with a 5-minute acquisition interval. By sequentially measuring the buoyant mass of individual, glioblastoma patient-derived tumor spheroids in media of different densities and cell permeabilities, we determine the absolute and fractional (v/v) water content of the spheroids, along with their dry mass, volume, and density properties. We achieve ~0.4% precision error in fractional water content with a throughput of 3 spheroids per hour. This enables us to detect both inter-spheroid variability in fractional water content and acute responses to kinase inhibition. Overall, we establish a simple and accessible technique for quantifying water content in living 3D cell culture models, opening new avenues for studying biophysical regulation in multicellular systems.

bioengineering↗

bioRxiv2025

Biophysical and molecular mechanisms responsible for phytoplankton sinking in response to starvation

Marine phytoplankton face eco-evolutionary pressure to regulate their vertical position in the ocean to access light, which is abundant towards the surface, and nutrients, which are found deeper down the water column. All phytoplankton experience gravitational sinking, which can contribute to their vertical migration. However, the biophysical and molecular mechanisms that impact gravitational sinking have not been systematically characterized across taxa and environmental conditions. Here, we combine simulations with measurements of cell mass, volume, and composition to investigate the effects of nutrient availability on gravitational sinking in 9 representative unicellular pico- and nanoplankton species. We find that gravitational sinking becomes faster in most species when starved, but the biophysical changes responsible for this vary across species and starvation conditions. For example, the faster sinking of Chaetoceros calcitrans is nearly exclusively driven by cell density whereas that of Emiliania huxleyi is due to cell volume. On the molecular level, the altered sinking is predominantly attributed to changes in cellular dry contents, rather than water. For example, starch accumulation increases sinking in 3 green algae species, and lipid accumulation decreases sinking in Phaeodactylum tricornutum. Overall, our work reveals that phytoplankton physiology has evolved multiple mechanisms that impact gravitational sinking in response to starvation, possibly to support the vertical migration of the cell.

cell biology↗

bioRxiv2024

Bimodal cell mass distribution separates CD8+ T cells into two distinct types with divergentdifferentiation dynamics

T cells are central to immune defense, yet existing molecular and phenotypic assays do not fully capture a cells intrinsic immune potential. Here we show that a single physical property, buoyant mass, reveals hidden heterogeneity within phenotypically similar, resting CD8+ T cells. Using suspended microchannel resonator measurements, we identify two distinct populations: "light" cells, enriched for mitochondrial content but prone to delayed activation and exhaustion, and "heavy" cells, biosynthetically poised for proliferation and memory formation. In patients with melanoma receiving immune checkpoint blockade, pre-treatment buoyant mass profiling of circulating T cells predicted therapeutic response with an accuracy comparable with standard tumor-derived biomarkers. Our findings establish buoyant mass as a label-free, stimulation-independent measure of systemic T cell fitness, providing a rapid and broadly applicable framework for immune profiling and response prediction in cancer and beyond.

biophysics↗

bioRxiv2023

Direct quantification of sinking velocities across unicellular algae

Eukaryotic phytoplankton, also known as algae, form the basis of marine food webs and drive marine carbon sequestration when their biomass sinks to the ocean floor. Algae must regulate their vertical movement, as determined by motility and gravitational sinking, to balance access to light at the surface and nutrients in deeper layers. However, the regulation of gravitational sinking velocities remains largely unknown, especially in motile species. Here, we directly quantify single-cell masses and volumes to calculate sinking velocities according to Stokes law in diverse clades of unicellular marine microalgae. Our results reveal the cell size, light, and nutrient-dependency of sinking velocities. We identify motile dinoflagellate and green algal species that increase their sinking velocity in response to starvation. Mechanistically, this increased cell sinking is achieved by photosynthesis-driven accumulation of carbohydrates, which increases cell mass and density. Moreover, cell sinking velocities correlate inversely with proliferation rates, and the mechanism regulating cell sinking velocities integrates signals from multiple nutrients. Our findings suggest that the regulation of cell composition according to environmental conditions contributes to the vertical movement of motile cells in the oceans. More broadly, our approach for sinking velocity measurements expands the study of gravitational sinking to motile cells and supports the modeling of marine carbon pump and nutrient cycles.

ecology↗