Biology subjects

Pullarkat, P.

Publications and source records attributed to Pullarkat, P..

3 recordsLinked to original sources

bioRxiv2025

Myosin II independent contraction of actin filaments in membrane nanotubes

The ability to generate active stresses within filamentous actin matrices is a fundamental and evolutionarily conserved process driving locomotion and morphogenetic changes in cells. The generation of pushing forces by actin polymerization is reasonably well understood, and is known to drive lamellipodia based motility and filopodial extension. Actin filaments decorated with myosin motors can also generate contractile stresses as in the cell cortex or in cytokinetic rings. In this article we use membrane nanotubes pulled out of axonal shaft to investigate actin dynamics and force generation. We report cyclic growth and retraction dynamics of actin within the tube and correlated contraction events giving rise to sustained load and fail cycles. The contraction mechanism operate independent of myosin II motor proteins. Furthermore, we analyzed the dynamics of actin within the tube, including under various biochemical or genetic perturbations. By combining these results with physical modeling, we argue that stresses generated in the actin filaments by the binding of actin depolymerizing factor (ADF/cofilin) proteins can explain the cyclic load-fail behavior.

biophysics↗

bioRxiv2025

Initiation and maturation of the early axonal βII-spectrin membrane-associated periodic skeleton requires active cytoskeletal remodelling

The axonal membrane-associated periodic skeleton (MPS), consisting of F-actin rings crosslinked by spectrin heterotetramers, is ubiquitous and critical for neuronal function and homoeostasis. However, the initiation and early development of the axonal MPS are poorly understood. Using superresolution imaging, we show that {beta}II-spectrin is recruited early to the axonal cortex, followed by progressive establishment of long-range periodic order. Microtubule dynamics are essential for MPS formation in the early stages, but transition to a passive stabilising role in mature axons. We show that the early subplasmalemmal recruitment of {beta}II-spectrin is dependent on cortical actin but not on actomyosin contractility, and active nucleation of F-actin is required in early development but is dispensable for the mature MPS. Using a {beta}II-spectrin knockout model, we demonstrate that the actin-binding and lipid-interacting domains of {beta}II-spectrin are critical for its subplasmalemmal confinement and, subsequently, MPS maturation. These findings highlight stage-specific cytoskeletal remodelling underlying MPS development and advance our understanding of axonal subcellular architecture.

neuroscience↗

bioRxiv2017

Mechanochemical feedback and control of endocytosis and membrane tension

Plasma membrane tension is an important factor that regulates many key cellular processes. Membrane trafficking is tightly coupled to membrane tension and can modulate the latter by addition or removal of the membrane. However, the cellular pathway(s) involved in these processes are poorly understood. Here we find that, among a number of endocytic processes operating simultaneously at the cell surface, a dynamin and clathrin-independent pathway, the CLIC/GEEC (CG) pathway, is rapidly and specifically upregulated upon reduction of tension. On the other hand, inhibition of the CG pathway results in lower membrane tension, while up regulation significantly enhances membrane tension. We find that vinculin, a well-studied mechanotransducer, mediates the tension-dependent regulation of the CG pathway. Vinculin negatively regulates a key CG pathway regulator, GBF1, at the plasma membrane in a tension dependent manner. Thus, the CG pathway operates in a negative feedback loop with membrane tension which leads to a homeostatic regulation of membrane tension.

cell biology↗