Abstract
Intracellular membrane nanotube formation and its dynamics play important roles for cargo transportation and organelle biogenesis. Regarding the regulation mechanisms, while much attention has been paid on the lipid composition and its associated protein molecules, effects of the vesicle size has not been studied in the cell. Giant unilamellar vesicles (GUVs) are often used for in vitro membrane deformation studies, but they are much larger than most intracellular vesicles and the in vitro studies also lack physiological relevance. Here, we use lysosomes and autolysosomes, whose sizes range between 100 nm and 1 μm, as model systems to study the size effects on nanotube formation both in vivo and in vitro. Single molecule observations indicate that driven by kinesin motors, small vesicles (100–200 nm) are mainly transported along the tracks while a remarkable portion of large vesicles (500–1000 nm) form nanotubes. This size effect is further confirmed by in vitro reconstitution assays on liposomes and purified lysosomes and autolysosomes. We also apply Atomic Force Microscopy (AFM) to measure the initiation force for nanotube formation. These results suggest that the size-dependence may be one of the mechanisms for cells to regulate cellular processes involving membrane-deformation, such as the timing of tubulation-mediated vesicle recycling.
Highlights
Biological membrane nanotubes are tubular structures that are commonly observed within the cell and between cells
The data show that the mean size of autolysosomes is similar with the measurements in the cell, whereas the size of lysosomes was only about 100 nm, much smaller than that measured in the cell using Fluorescence microscopy (FM)
Compared with previous in vitro studies on Giant unilamellar vesicles (GUVs), our work provides the first set of direct evidence to support the physiological relevance of vesicle sizes in regulation of nanotube formation and its dynamics
Summary
Biological membrane nanotubes are tubular structures that are commonly observed within the cell and between cells. Components that are thought to be involved in membrane tubulation are either synthesized, purified or even kept in cell extracts and used to reconstitute the tubulation process This approach has helped to make reduction of required components for nanotube formation[9]. Direct single vesicle manipulation techniques are used in these assays, including hydrodynamic flow[13], micropipettes[14] and optical tweezers[15,16] As these techniques allow to control the load precisely, the mechanical response of membrane tubulation may be studied in details. We apply Atomic Force Microscopy (AFM) to quantitatively measure the force barrier during the tubulation process and carry a simple computation based on the measurements Overall, these results suggest that vesicle size affects the tubulation probability for lysosomes and autolysosomes, whose size ranges between 50 nm and several micrometers. The size-dependence effect may be one of the mechanisms for the cell to regulate cellular processes involving membrane-deformation
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
