Discovery And Ultrastructural Study On Migrasome

As migrating cells move,they leave retraction fibers behind them.Large vesicles with monolayer membrane grow on the tips and intersections of retraction fibers,we named them “migrasomes”.When migrating cells leave,migrasomes still stay in the original position,break,or directly taken up by surrounding cells.So migrasome is one approach can transfer cellular contents between cells.It may play a role in regulating intracellular homeostasis,cell viability,differentiation,metabolism and other physiological processes as well as cancer,infectious diseases and other pathological processes.In this manuscript,we first describe the ultrastructure of the migrasome by electron microscopy in order to provide an important morphological basis for study on formation and related molecular mechanism of migrasome.We first found migrasome has pomegranate-like structures with diameters up to 3 ?m and contains smaller vesicles with diameters about 50-100 nm under transmission electron microscopy(TEM).The number of smaller vesicles varies greatly,some structures contain up to 300 vesicles,while most contain fewer than 10.TEM and scanning electron microscopy(SEM)analysis revealed that migrasomes are connected to cell body by retraction fibers.The partial 3D architecture of migrasome full filled with vesicles was reconstructed using electron tomography,3D rendering result showed that the vesicles were not fused with the out membrane of migrasome.TEM confirmed that structures with the same morphological characteristics of migrasome were highly enriched in one of the fractions which provided a precondition for screening of migrasome associated protein.We carried out correlative light and electron microscopy analysis and found that TSPAN4-positive ring-like structures are indeed migrasomes observed by TEM/SEM,which verified that TSPAN4 protein is localized on migrasome.In this manuscript,high-pressure freezing fixation method is applied to confirm microtubule and actin filament are present in retraction fiber.Migrasomes are present in many different cell types in vitro by live-cell imaging.TEM analysis reveals that migrasome-like structures are present in various tissue of mouse,rat,zebrafish embryo and chicken embryo.Migrasome-like structures are also present in DSS induced inflammatory model.The 3D architecture of migrasome-like structure around T cell was reconstructed using focused ion beam scanning electron microscope.