Systematic analysis of curvature-dependent lipid dynamics in a stochastic 3D membrane model.

To minimize the free energy of the system, lipid membranes display curvature-dependent rearrangements at the local and global scale. The optimal membrane shape is generally approximated by averaging the curvature preference of individual lipids across the whole surface. Potential stress due to imperfections in lipid packing caused by local lipid inhomogeneities, however, is frequently neglected.

Dendrite tapering actuates a self-organizing signaling circuit for stochastic filopodia initiation in neurons.

How signaling units spontaneously arise from a noisy cellular background is not well understood. Here, we show that stochastic membrane deformations can nucleate exploratory dendritic filopodia, dynamic actin-rich structures used by neurons to sample its surroundings for compatible transcellular contacts. A theoretical analysis demonstrates that corecruitment of positive and negative curvature-sensitive proteins to deformed membranes minimizes the free energy of the system, allowing the formation of long-lived curved membrane sections from stochastic membrane fluctuations.

ArhGEF37 assists dynamin 2 during clathrin-mediated endocytosis.

Clathrin-mediated endocytosis (CME) engages over 30 proteins to secure efficient cargo and membrane uptake. While the function of most core CME components is well established, auxiliary mechanisms crucial for fine-tuning and adaptation remain largely elusive. In this study, we identify ArhGEF37, a currently uncharacterized protein, as a constituent of CME.

Polarized microtubule dynamics directs cell mechanics and coordinates forces during epithelial morphogenesis.

Coordinated rearrangements of cytoskeletal structures are the principal source of forces that govern cell and tissue morphogenesis. However, unlike for actin-based mechanical forces, our knowledge about the contribution of forces originating from other cytoskeletal components remains scarce. Here, we establish microtubules as central components of cell mechanics during tissue morphogenesis.

Self-organization across scales: from molecules to organisms.

Creating ordered structures from chaotic environments is at the core of biological processes at the subcellular, cellular and organismic level. In this perspective, we explore the physical as well as biological features of two prominent concepts driving self-organization, namely phase transition and reaction-diffusion, before closing with a discussion on open questions and future challenges associated with studying self-organizing systems.This article is part of the theme issue 'Self-organization in cell biology'.

A Graphical User Interface for Software-assisted Tracking of Protein Concentration in Dynamic Cellular Protrusions.

Filopodia are dynamic, finger-like cellular protrusions associated with migration and cell-cell communication. In order to better understand the complex signaling mechanisms underlying filopodial initiation, elongation and subsequent stabilization or retraction, it is crucial to determine the spatio-temporal protein activity in these dynamic structures. To analyze protein function in filopodia, we recently developed a semi-automated tracking algorithm that adapts to filopodial shape-changes, thus allowing parallel analysis of protrusion dynamics and relative protein concentration along the whole filopodial length.

Automated analysis of filopodial length and spatially resolved protein concentration via adaptive shape tracking.

Filopodia are dynamic, actin-rich structures that transiently form on a variety of cell types. To understand the underlying control mechanisms requires precise monitoring of localization and concentration of individual regulatory and structural proteins as filopodia elongate and subsequently retract. Although several methods exist that analyze changes in filopodial shape, a software solution to reliably correlate growth dynamics with spatially resolved protein concentration along the filopodium independent of bending, lateral shift, or tilting is missing.

Simultaneous measurement of mass and rotation of trapped absorbing particles in air.

We trap absorbing micro-particles in air by photophoretic forces generated using a single loosely focused Gaussian trapping beam. We measure a component of the radial Brownian motion of a trapped particle cluster and determine the power spectral density, mean squared displacement, and normalized position and velocity autocorrelation functions to characterize the photophoretic body force in a quantitative fashion for the first time. The trapped particles also undergo spontaneous rotation due to the action of this force.