Actin Reorganization in Drosophila Syncytial Blastoderm Embryos: a Dissertation

Publication Date

January 2002

Document Type

Doctoral Dissertation


Graduate School of Biomedical Sciences, Department of Molecular Genetics & Microbiology


Actins; Cell Cycle Proteins; Drosophila Proteins; Giant Cells; Academic Dissertations


This work addresses the mechanism of cell cycle specific actin reorganization in Drosophila syncytial blastoderm embryos. During mitosis in typical animal cells after chromosome segregation is complete, daughter cells are separated in a process called cytokinesis. Cytokinesis is ordinarily driven by constriction of an actin ring that physically pinches the cell in two. The early Drosophila embryo is a syncytium; nuclei divide in a single cell without intervening cytokinesis. During the later syncytial divisions, nuclei are arranged in a monolayer at the cortex of the embryo. This stage of embryogenesis is characterized by cycles of actin reorganization that are coordinated with the nuclear division cycles. Since several components of typical cleavage furrows function in this cell cycle driven actin reorganization, the syncytial blastoderm has been used as a model system to better understand cell cycle driven actin reorganization in typical cells. The syncytial Drosophila embryo is easily manipulated genetically, cytoskeletal structures can be visualized in both fixed and living embryos, and large quantities of embryos are attainable for biochemical analysis. We have therefore chosen this model system to study actin reorganization. We show that actin reorganization in syncytial embryos is coordinated by cell cycle cues similar to those utilized in typical cells. Drosophila embryo actin reorganization has several unique features, however. For instance, actin reorganization appears to be associated with centrosomes in a process that does not require microtubules. In addition, the driving force for formation of Drosophila cleavage structures may be actin filament polymerization, rather than contraction of an acto-myosin ring. Whether these characteristics of Drosophila embryo actin reorganization typifies actin reorganization in other cells remains to be seen.


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