title: Calcium waves occur as Drosophila oocytes activate.
abstract: Egg activation is the process by which a mature oocyte becomes capable of supporting embryo development. In vertebrates and echinoderms, activation is induced by fertilization. Molecules introduced into the egg by the sperm trigger progressive release of intracellular calcium stores in the oocyte. Calcium wave(s) spread through the oocyte and induce completion of meiosis, new macromolecular synthesis, and modification of the vitelline envelope to prevent polyspermy. However, arthropod eggs activate without fertilization: in the insects examined, eggs activate as they move through the female's reproductive tract. Here, we show that a calcium wave is, nevertheless, characteristic of egg activation in Drosophila. This calcium rise requires influx of calcium from the external environment and is induced as the egg is ovulated. Pressure on the oocyte (or swelling by the oocyte) can induce a calcium rise through the action of mechanosensitive ion channels. Visualization of calcium fluxes in activating eggs in oviducts shows a wave of increased calcium initiating at one or both oocyte poles and spreading across the oocyte. In vitro, waves also spread inward from oocyte pole(s). Wave propagation requires the IP3 system. Thus, although a fertilizing sperm is not necessary for egg activation in Drosophila, the characteristic of increased cytosolic calcium levels spreading through the egg is conserved. Because many downstream signaling effectors are conserved in Drosophila, this system offers the unique perspective of egg activation events due solely to maternal components.
authors.affiliation: Department of Biological Sciences, Tokyo Metropolitan University, Tokyo 192-0397, Japan;
authors.forename: Taro
authors.initials: T
authors.lastname: Kaneuchi
authors.affiliation: Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853; and.
authors.forename: Caroline V
authors.initials: CV
authors.lastname: Sartain
authors.affiliation: Faculty of Life and Environmental Sciences and Life Science Center of Tsukuba Advanced Research Alliance (TARA), University of Tsukuba, Ibaraki 305-8572, Japan.
authors.forename: Satomi
authors.initials: S
authors.lastname: Takeo
authors.affiliation: Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853; and.
authors.forename: Vanessa L
authors.initials: VL
authors.lastname: Horner
authors.affiliation: Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853; and.
authors.forename: Norene A
authors.initials: NA
authors.lastname: Buehner
authors.affiliation: Department of Biological Sciences, Tokyo Metropolitan University, Tokyo 192-0397, Japan; mfw5@cornell.edu aigaki-toshiro@tmu.ac.jp.
authors.forename: Toshiro
authors.initials: T
authors.lastname: Aigaki
authors.affiliation: Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853; and mfw5@cornell.edu aigaki-toshiro@tmu.ac.jp.
authors.forename: Mariana F
authors.initials: MF
authors.lastname: Wolfner
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004330:Drosophila / Q000166:cytology / Q000378:metabolism*; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D017136:Ion Transport; D009865:Oocytes / Q000378:metabolism*
chemical_list: D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium
keywords: calcium; egg activation; fertilization; mechanosensitive ion channels; oocyte