These panels show the localization of actin filaments (red) and nuclei (blue) during the stages of oogenesis as a mature Drosophila egg is made. The Drosophila egg or oocyte develops with the assistance of 15 nurse cells (A). A layer of somatic follicle cells surrounds the developing egg and nurse cells forming an egg-making unit or egg chamber (A). The nurse cells are responsible for generating most of the nutrients and macromolecules the egg will need to start development following fertilization. These nutrients and macromolecules are transported into the oocyte through channels lined with actin called ring canals that connect the nurse cells to each other and to the oocyte (A). During the early stages of oogenesis, this transport is relatively slow. Near the end of oogenesis, a network of actin and myosin that underlies the plasma membrane of each nurse cell contracts pushing the contents of the nurse cells into the oocyte. Just prior to this contraction cytoplasmic actin filaments form between the large nurse cell nuclei and the nurse cell plasma membrane (B). These filaments are thought to hold the nucleus in place during contraction, preventing it from being forced into the ring canals and blocking movement of the nurse cell contents into the oocyte. Following contraction, the nurse cells consist only of a large nucleus surrounded by plasma membrane (C). Shortly after this the nurse cells will undergo programmed cell death, the follicle cells will produce the eggshell and the oocyte will be ready to be fertilized. Images taken by Lindsay Regruto '12.
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