title: Exocyst-Dependent Membrane Addition Is Required for Anaphase Cell Elongation and Cytokinesis in Drosophila.
abstract: Mitotic and cytokinetic processes harness cell machinery to drive chromosomal segregation and the physical separation of dividing cells. Here, we investigate the functional requirements for exocyst complex function during cell division in vivo, and demonstrate a common mechanism that directs anaphase cell elongation and cleavage furrow progression during cell division. We show that onion rings (onr) and funnel cakes (fun) encode the Drosophila homologs of the Exo84 and Sec8 exocyst subunits, respectively. In onr and fun mutant cells, contractile ring proteins are recruited to the equatorial region of dividing spermatocytes. However, cytokinesis is disrupted early in furrow ingression, leading to cytokinesis failure. We use high temporal and spatial resolution confocal imaging with automated computational analysis to quantitatively compare wild-type versus onr and fun mutant cells. These results demonstrate that anaphase cell elongation is grossly disrupted in cells that are compromised in exocyst complex function. Additionally, we observe that the increase in cell surface area in wild type peaks a few minutes into cytokinesis, and that onr and fun mutant cells have a greatly reduced rate of surface area growth specifically during cell division. Analysis by transmission electron microscopy reveals a massive build-up of cytoplasmic astral membrane and loss of normal Golgi architecture in onr and fun spermatocytes, suggesting that exocyst complex is required for proper vesicular trafficking through these compartments. Moreover, recruitment of the small GTPase Rab11 and the PITP Giotto to the cleavage site depends on wild-type function of the exocyst subunits Exo84 and Sec8. Finally, we show that the exocyst subunit Sec5 coimmunoprecipitates with Rab11. Our results are consistent with the exocyst complex mediating an essential, coordinated increase in cell surface area that potentiates anaphase cell elongation and cleavage furrow ingression.
authors.affiliation: Istituto di Biologia e Patologia Molecolari del CNR, Dipartimento di Biologia e Biotecnologie, Università Sapienza di Roma, Roma, Italy.
authors.forename: Maria Grazia
authors.initials: MG
authors.lastname: Giansanti
authors.affiliation: Department of Physics, University of Denver, Denver, Colorado, United States of America.
authors.forename: Timothy E
authors.initials: TE
authors.lastname: Vanderleest
authors.affiliation: Department of Biological Sciences, University of Denver, Denver, Colorado, United States of America.
authors.forename: Cayla E
authors.initials: CE
authors.lastname: Jewett
authors.affiliation: Istituto di Biologia e Patologia Molecolari del CNR, Dipartimento di Biologia e Biotecnologie, Università Sapienza di Roma, Roma, Italy.
authors.forename: Stefano
authors.initials: S
authors.lastname: Sechi
authors.affiliation: Istituto di Biologia e Patologia Molecolari del CNR, Dipartimento di Biologia e Biotecnologie, Università Sapienza di Roma, Roma, Italy.
authors.forename: Anna
authors.initials: A
authors.lastname: Frappaolo
authors.affiliation: Cell Biology Program, The Hospital for Sick Children, Toronto, Ontario, Canada.
authors.forename: Lacramioara
authors.initials: L
authors.lastname: Fabian
authors.affiliation: Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, Virginia, United States of America.
authors.forename: Carmen C
authors.initials: CC
authors.lastname: Robinett
authors.affiliation: Cell Biology Program, The Hospital for Sick Children, Toronto, Ontario, Canada; Department of Molecular Genetics, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Julie A
authors.initials: JA
authors.lastname: Brill
authors.affiliation: Department of Physics, University of Denver, Denver, Colorado, United States of America.
authors.forename: Dinah
authors.initials: D
authors.lastname: Loerke
authors.affiliation: Department of Developmental Biology, Stanford University School of Medicine, Stanford, California, United States of America.
authors.forename: Margaret T
authors.initials: MT
authors.lastname: Fuller
authors.affiliation: Department of Biological Sciences, University of Denver, Denver, Colorado, United States of America.
authors.forename: J Todd
authors.initials: JT
authors.lastname: Blankenship
mesh_terms: D000705:Anaphase; D000818:Animals; D002453:Cell Cycle; D004330:Drosophila / Q000166:cytology*