A single and rapid calcium wave at egg activation in Drosophila

Journal article

Activation is an essential process that accompanies fertilisation in all animals and heralds major cellular changes, most notably, resumption of the cell cycle. While activation involves wave-like oscillations in intracellular Ca²⁺ concentration in mammals, ascidians and polychaete worms and a single Ca²⁺ peak in fish and frogs, in insects, such as Drosophila, to date, it has not been shown what changes in intracellular Ca²⁺ levels occur. Here, we utilise ratiometric imaging of Ca²⁺ indicator dyes and genetically encoded Ca²⁺ indicator proteins to identify and characterise a single, rapid, transient wave of Ca²⁺ in the Drosophila egg at activation. Using genetic tools, physical manipulation and pharmacological treatments we demonstrate that the propagation of the Ca²⁺ wave requires an intact actin cytoskeleton and an increase in intracellular Ca²⁺ can be uncoupled from egg swelling, but not from progression of the cell cycle. We further show that mechanical pressure alone is not sufficient to initiate a Ca²⁺ wave. We also find that processing bodies, sites of mRNA decay and translational regulation, become dispersed following the Ca²⁺ transient. Based on this data we propose the following model for egg activation in Drosophila: exposure to lateral oviduct fluid initiates an increase in intracellular Ca²⁺ at the egg posterior via osmotic swelling, possibly through mechano-sensitive Ca²⁺ channels; a single Ca²⁺ wave then propagates in an actin dependent manner; this Ca²⁺ wave co-ordinates key developmental events including resumption of the cell cycle and initiation of translation of mRNAs such as bicoid.

Authors: York-Andersen, A; Parton, R; Bi, C; Bromley, C; Davis, I

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Company of Biologists
• Journal: Biology Open
• Volume: 4
• Issue: 4
• Pages: 553-560
• Publication date: 2015-03-06
• Acceptance date: 2015-01-26
• DOI: 10.1242/​bio.201411296
• EISSN: 2046-6390
• Language: English
• Keywords: calcium imaging; Drosophila; calcium transient; egg activation