Effects of ionomycin on egg activation and early development in starfish.

Ionomycin is a Ca(2+)-selective ionophore that is widely used to increase intracellular Ca(2+) levels in cell biology laboratories. It is also occasionally used to activate eggs in the clinics practicing in vitro fertilization. However, neither the precise molecular action of ionomycin nor its secondary effects on the eggs' structure and function is well known.

The biphasic increase of PIP2 in the fertilized eggs of starfish: new roles in actin polymerization and Ca2+ signaling.

Background: Fertilization of echinoderm eggs is accompanied by dynamic changes of the actin cytoskeleton and by a drastic increase of cytosolic Ca(2+). Since the plasma membrane-enriched phospholipid phosphatidylinositol 4,5-bisphosphate (PIP2) serves as the precursor of inositol 1,4,5 trisphosphate (InsP(3)) and also regulates actin-binding proteins, PIP2 might be involved in these two processes.

Methodology/principal Findings: In this report, we have studied the roles of PIP2 at fertilization of starfish eggs by using fluorescently tagged pleckstrin homology (PH) domain of PLC-δ1, which has specific binding affinity to PIP2, in combination with Ca(2+) and F-actin imaging techniques and transmission electron microscopy.

Guanine nucleotides in the meiotic maturation of starfish oocytes: regulation of the actin cytoskeleton and of Ca(2+) signaling.

Background: Starfish oocytes are arrested at the first prophase of meiosis until they are stimulated by 1-methyladenine (1-MA). The two most immediate responses to the maturation-inducing hormone are the quick release of intracellular Ca(2+) and the accelerated changes of the actin cytoskeleton in the cortex. Compared with the later events of oocyte maturation such as germinal vesicle breakdown, the molecular mechanisms underlying the early events involving Ca(2+) signaling and actin changes are poorly understood.

Alteration of the cortical actin cytoskeleton deregulates Ca2+ signaling, monospermic fertilization, and sperm entry.

Background: When preparing for fertilization, oocytes undergo meiotic maturation during which structural changes occur in the endoplasmic reticulum (ER) that lead to a more efficient calcium response. During meiotic maturation and subsequent fertilization, the actin cytoskeleton also undergoes dramatic restructuring. We have recently observed that rearrangements of the actin cytoskeleton induced by actin-depolymerizing agents, or by actin-binding proteins, strongly modulate intracellular calcium (Ca2+) signals during the maturation process.

Actin cytoskeleton modulates calcium signaling during maturation of starfish oocytes.

Before successful fertilization can occur, oocytes must undergo meiotic maturation. In starfish, this can be achieved in vitro by applying 1-methyladenine (1-MA). The immediate response to 1-MA is the fast Ca2+ release in the cell cortex.