The part played by inositol trisphosphate and calcium in the propagation of the fertilization wave in sea urchin eggs.

Abstract

Abstract. Sea urchin egg activation at fertilization is progressive, beginning at the point of sperm entry and moving across the egg with a velocity of 5 ~tm/s. This activation wave (Kacser, H., 1955, J. Exp. Biol., 32:451-467) has been suggested to be the result of a progressive release of calcium from a store within the egg cytoplasm (Jaffe, L. E, 1983, Dev. Biol., 99:265-276). The progressive release of calcium may be due to the production of inositol trisphosphate (InsP3), a second messenger. We show here that (a) a wave of calcium release crosses the Lytechinus pictus egg; the peak of the wave travels with a velocity of 5 ~tm/s; (b) microinjection of InsP3 causes the release of calcium within the egg; (c) calcium release (as judged by fertilization envelope elevation) is abolished by prior injection of the calcium chelator EGTA; (d) neomycin, an inhibitor of InsP3 production, does not prevent the release of calcium in response to InsP3 but does abolish the wave of calcium release; (e) the egg cytoplasm rapidly buffers microinjected calcium; (f) the calcium concentration required to cause fertilization membrane elevation when microinjected is very similar to that required to stimulate the production of InsP3 in vitro; and (g) the progressive fertilization membrane elevation seen after microinjection of calcium buffers appears to be due to diffusion of the buffer across the egg cytoplasm rather than to the induction of the activation wave. We conclude that InsP3 diffuses through the egg cytoplasm much more readily than calcium ions and that calcium-stimulated production of InsP3 and InsP3-induced calcium release from an internal store can account for the progressive release of calcium at fertilization.

Fertilization and Nicotinic Acid Adenine Dinucleotide Phosphate Induce pH Changes in Acidic Ca2+ Stores in Sea Urchin Eggs

“…Only the latter was previously detected in asynchronous populations of eggs (10), hardly surprising when the transient pH L ASH only extends 15-25 m into the cortex (in an egg ϳ120 m in diameter). Moreover, alkalinization propagated as a wave around the egg cortex at ϳ5 m/s, a velocity similar to the main [Ca 2ϩ ] i wave and the exocytotic lifting of the fertilization envelope (26,27). At higher magnification, the alkalinization wave was manifest as the summation of smaller events (pH L ARES, 2-3 m in diameter) that appear to represent alkalinization at the individual vesicle level.…”

Calcium signalling in early embryos

“…This was first shown in the sea urchin egg (Zucker & Steinhardt 1978) and later confirmed (Swann & Whitaker 1986;Swann et al 1992) by microinjection of the tetracarboxylate calcium chelator EGTA. Microinjection of EGTA was also shown to prevent the activation of mouse (Miyazaki & Igusa 1982) and ascidian oocytes ( Tosti & Dale 1994).…”

“…The microinjection of InsP 3 at sub-micromolar concentrations will activate frog (Nuccitelli et al 1993), sea urchin (Whitaker & Irvine 1984;Swann & Whitaker 1986;Turner et al 1986), starfish (Picard et al 1985;Santella et al 2000), ascidian Roegiers et al 1995) and mouse eggs (Swann et al 1989). These commonly studied species are all deuterostomes.…”

“…Aequorin was also used eventually to measure a large free calcium increase in the mouse oocyte (Cuthbertson et al 1981) and image intensification was used to record calcium waves in the smaller (relative to Medaka) sea urchin and starfish eggs Swann & Whitaker 1986). A calcium wave was also measured in frog eggs using calcium-sensitive microelectrodes (Busa & Nuccitelli 1985).…”

Cytochemical Ca2+ Distribution in Activated Discoglossus pictus Eggs: A Gradient in the Predetermined Site of Fertilization

“…Such an increase, physiologically triggered by the sperm, functions as a second messenger which mediates many early and late activities of the fertilizing egg (11,21). Now it is known that Ca2+ is mobilized from intracellular storage sites in response to the release of inositol-(1, 4, 5)-triphosphate (IP3) from the plasma membrane, which is supposed to open IP3-gated Ca2+-channels located in the store membrane (2,3,33,35,4,30,22). In several species, extensive networks of the smooth endoplasmic reticulum (SER) are arranged in both the cortical and the deeper regions of the egg cytoplasm, thus possibly functioning as Ca2+ sources and sinks at activation (6,13,29,24,14).…”