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Vol. 19, Issue 6, 2363-2372, June 2008

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Proper Cellular Reorganization during Drosophila Spermatid Individualization Depends on Actin Structures Composed of Two Domains, Bundles and Meshwork, That Are Differentially Regulated and Have Different Functions

Tatsuhiko Noguchi^*,, Marta Lenartowska^,, Aaron D. Rogat^,||, Deborah J. Frank, and Kathryn G. Miller

Department of Biology, Washington University in St. Louis, St. Louis, MO 63130; Faculty of Biology and Earth Sciences, Institute of General and Molecular Biology, Laboratory of Developmental Biology, Nicolaus Copernicus University, 87-100 Torun, Poland; and *Laboratory for Morphogenetic Signaling, Center for Developmental Biology, RIKEN Kobe, Kobe 650-0047, Japan

Submitted August 27, 2007; Revised February 20, 2008; Accepted March 4, 2008
Monitoring Editor: David Drubin

During spermatid individualization in Drosophila, actin structures (cones) mediate cellular remodeling that separates the syncytial spermatids into individual cells. These actin cones are composed of two structural domains, a front meshwork and a rear region of parallel bundles. We show here that the two domains form separately in time, are regulated by different sets of actin-associated proteins, can be formed independently, and have different roles. Newly forming cones were composed only of bundles, whereas the meshwork formed later, coincident with the onset of cone movement. Polarized distributions of myosin VI, Arp2/3 complex, and the actin-bundling proteins, singed (fascin) and quail (villin), occurred when movement initiated. When the Arp2/3 complex was absent, meshwork formation was compromised, but surprisingly, the cones still moved. Despite the fact that the cones moved, membrane reorganization and cytoplasmic exclusion were abnormal and individualization failed. In contrast, when profilin, a regulator of actin assembly, was absent, bundle formation was greatly reduced. The meshwork still formed, but no movement occurred. Analysis of this actin structure's formation and participation in cellular reorganization provides insight into how the mechanisms used in cell motility are modified to mediate motile processes within specialized cells.

These authors contributed equally to this work.

^|| Present address: Consortium for Policy Research in Education, University of Pennsylvania, 3440 Market Street, Suite 560, Philadelphia, PA 19104-3325.

Address correspondence to: Kathryn G. Miller (miller{at}wustl.edu)