Mount Holyoke College

In vivo cytoskeletal dynamics of living fish embryos
Movie #5:Actin Dynamics in Apical Protrusive Activity

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As in Movie #4, this video shows the dynamics of the apical cell surface of individual cells of the enveloping layer in a killifish embryo. The fluorescent actin is seen to polymerize and depolymerize in cyclic waves that extend and retract these surface protrusions. You are looking at two neighboring cells expressing the fluorescent GFP-actin. The rest of the frame (that looks completely black) is not empty--attached cells form a continuous epithelium. You don't see these cells under fluorescent microscopy, however, because these particular cells did not express the GFP-actin gene. In our hands, the expression of this inserted gene is mosaic, with some cells expressing it (i.e., making the fluorescent protein product), and others not. These "black cells" are still making actin, and in the light microscope they look completely normal. This mosaic expression is quite a boon for our research, because we can see events happening at the margins of neighboring cells especially well.