During cytokinesis, the membrane constricts and the cytosol is equally separated into two daughter cells. At the end of this step the cells remain connected by an intercellular bridge composed of membranes and microtubules. Completion of cytokinesis, termed abscission, is mediated by membrane fission driven by the ESCRT protein complex. While much is known on ESCRT mediated abscission through cell culture experiments, little is known about this process during embryonic development and in the whole organism. Zebrafish (Danio rerio) early embryonic stages are diverse and can be used to investigate cytokinesis and abscission in different contexts: for example comparing cytokinesis in different cell sizes and during synchronous (early blastula) or asynchronous (late blastula) divisions. To study abscission and ESCRT involvement in abscission during embryonic development, we established an assay to visualize ESCRT mediated abscission in live zebrafish embryos. Using this assay we visualize ESCRT proteins together with tubulin GFP for long periods in live developing embryos. Using this assay we investigate the spatiotemporal organization of ESCRT proteins in intercellular bridges of cells undergoing cytokinesis at different division cycles. We find that CEP55 localize to the microtubules fibers during early cytokinesis whereas TSG101 localizes to the intercellular bridge in late cytokinesis. Comparing the spatial characteristics of the intercellular bridge in cells at different division cycle, obtaining different cell size, we find that prior to abscission the intercellular bridge constricts to a typical diameter of ~ 1.25 μm regardless of cell size, these finding suggest a regulation on bridge diameter prior to abscission onset and ESCRT recruitment. Taken together our data indicate that Zebrafish embryonic developmental system is an ideal model system to investigate ESCRT mediated abscission during embryonic development. Our preliminary results already highlight new features of abscission that could not be studied using a tissue culture model.
