Adding from Top to Bottom

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Science  01 Sep 2000:
Vol. 289, Issue 5484, pp. 1433
DOI: 10.1126/science.289.5484.1433a

Drosophila embryos develop as a syncytium (containing 6000 nuclei) and then undergoes cellularization—a specialized type of cytokinesis—which involves the addition of membrane and the formation of 6000 polarized epithelial cells.

Lecuit and Wieschaus describe the delivery of intracellular membrane components first to the apical and then to the lateral surfaces of the forming cells. By labeling the cell surface and tracking particle movements in living embryos, they observed four phases of membrane growth and reorganization. In phase 1 invaginations develop that demarcate the individual cells; in phase 2 these furrows grow slowly, and the nuclei begin to elongate; in phase 3 the furrows extend more rapidly as distinct cells become more obvious; and in phase 4 cellularization is completed. Microtubules are required for membrane delivery, and membrane delivery is required continuously. In addition to creating a polarized distribution of membrane (old at the base and new at the apex) in these epithelial cells, membrane insertion may provide the impetus for furrow growth during cytokinesis. — SMH

J. Cell Biol.150, 849 (2000).

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