Biology subjects

Dharan, R.

Publications and source records attributed to Dharan, R..

3 recordsLinked to original sources

bioRxiv2023

Migrasome formation is initiated preferentially in tubular junctions by alternations of membrane tension or intracellular pressure

Migrasomes, the transient vesicle-like cellular organelles, arise on the retraction fibers (RFs), the branched tubular extensions of the plasma membrane generated during cell migration. Migrasomes form in two steps: a local RF swelling is followed by a protein-dependent stabilization of the emerging spherical bulge. Here we approached experimentally and theoretically the previously unaddressed mechanism of the initial RF swelling. We hypothesized that the swelling can be driven by alterations of the generic mechanical factors, the RFs luminal pressure and membrane tension. To examine the effects of pressure, we exposed migrating RF-producing cells to a hypotonic medium and observed the formation of migrasome-like bulges with a preferential location in the RF branching sites. To test the results of tension variations, we developed a biomimetic system of three membrane tubules connected by a junction and subjected to controlled membrane tension. An abrupt increase of tension resulted in a migrasome-like bulge formation in the junction and in the tubular regions. Following the formation, the tubules bulges moved toward and merged with the junctional bulge. To understand the physical forces behind the observations, we considered theoretically the mechanical energy of a membrane system consisting of a three-way tubular junction with emerging tubular arms connected to a membrane reservoir. The energy minimization predicted the membrane bulging, preferably, in the junction site as a result of both an increase in the luminal pressure and an abrupt rise of the membrane tension. We discuss the common physical background of the two phenomena.

biophysics↗

bioRxiv2022

Tetraspanin 4 mediates migrasome formation via a two-stage mechanism

Migrasomes are recently discovered signalling organelles, enriched with tetraspanin proteins (TSPAN)1. They form by local swelling of retraction fibers, the cylindrical protrusions of cell membranes that form as a result of cell migration along external substrates. Migrasomes can grow up to several micrometers in diameter2, and allow cells to release contents such as chemokines at specific locations, hence, transmitting signals to surrounding cells through the relevant chemokine receptors. Recently, evidence emerged showing that migrasomes play essential roles in fundamental cellular processes such transfer of mRNA and proteins3, organ morphogenesis4, and mitochondria quality control5. Thus, understanding the mechanism of migrasome biogenesis is of outstanding importance. Previously, it was established that the molecules crucial for migrasome formation are tetraspanin proteins and cholesterol forming macrodomains in the migrasome membrane, while the physical forces driving local swelling of the retraction fibers originate from membrane tension and bending rigidity1. Yet, it remained unknown how and in which time sequence these factors are involved in migrasome nucleation, growth, and stabilization, and what are the possible intermediate stages of migrasome biogenesis.

biophysics↗

bioRxiv2022

Transmembrane proteins tetraspanin 4 and CD9 sense membrane curvature

Multiple membrane shaping and remodelling processes are associated with tetraspanin proteins by yet unknown mechanisms. Tetraspanins constitute a family of proteins with four transmembrane domains present in high copy numbers in every cell type. Prominent examples are tetraspanin4 and CD9 that are required for the fundamental cellular processes of migrasome formation and fertilization, respectively. These proteins are enriched in curved membrane structures, such as cellular retraction fibers and oocyte microvilli. The factors driving this enrichment are, however, unknown. Here we revealed that tetrasapnin4 and CD9 are curvature sensors with a preference for positive membrane curvature. To this end we used a biomimetic system emulating membranes of cell retraction fibers and oocyte microvilli by membrane tubes pulled out of giant plasma membrane vesicles with controllable membrane tension and curvature. We developed a simple thermodynamic model for the partitioning of curvature sensors between flat and tubular membranes, which allowed us to estimate the individual intrinsic curvatures of the two proteins. Overall, our findings illuminate the process of migrasome formation and oocyte microvilli shaping and provide insight into the role of tetraspanin proteins in membrane remodelling processes.

biophysics↗