Dataset Information

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

ABSTRACT:

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-?1, which has specific binding affinity to PIP2, in combination with Ca(2+) and F-actin imaging techniques and transmission electron microscopy. During fertilization, PIP2 increased at the plasma membrane in two phases rather than continually decreasing. The first increase was quickly followed by a decrease about 40 seconds after sperm-egg contact. However, these changes took place only after the Ca(2+) wave had already initiated and propagated. The fertilized eggs then displayed a prolonged increase of PIP2 that was accompanied by the appearance of numerous spikes in the perivitelline space during the elevation of the fertilization envelope (FE). These spikes, protruding from the plasma membrane, were filled with microfilaments. Sequestration of PIP2 by RFP-PH at higher doses resulted in changes of subplasmalemmal actin networks which significantly delayed the intracellular Ca(2+) signaling, impaired elevation of FE, and increased occurrences of polyspermic fertilization.

Conclusions/significance

Our results suggest that PIP2 plays comprehensive roles in shaping Ca(2+) waves and guiding structural and functional changes required for successful fertilization. We propose that the PIP2 increase and the subsequent formation of actin spikes not only provide the mechanical supports for the elevating FE, but also accommodate increased membrane surfaces during cortical granule exocytosis.

SUBMITTER: Chun JT

PROVIDER: S-EPMC2990714 | biostudies-literature | 2010 Nov

REPOSITORIES: biostudies-literature

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Publications

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

Chun Jong T JT Puppo Agostina A Vasilev Filip F Gragnaniello Giovanni G Garante Ezio E Santella Luigia L

PloS one 20101123 11

<h4>Background</h4>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.<h4>Methodology/principal findings</h4>In this report, we have studied the roles of PIP2 at f ...[more]

PMID: 21124897

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Project description:The Ca2+ oscillations initiated by the fertilizing sperm (but terminating concomitant with pronucleus formation) apparently ensure that the events constituting egg activation occur in the correct temporal order; early events (e.g., cortical granule exocytosis) require fewer oscillations than later events (e.g., recruitment of maternal mRNA). Whether the Ca2+ signaling events impact long-term development, in particular development to term, is unknown. Using fertilized eggs that have undergone the first few Ca2+ oscillations, we developed procedures that result either in inhibiting or stimulating the natural pattern of Ca2+ signaling of inseminated eggs. Although the incidence of development to the blastocyst stage is unaltered by these procedures, fewer offspring are born following embryo transfer, indicating that developmental competence of the blastocysts is reduced. Interestingly, embryo transfer experiments reveal that when the natural regime of Ca2+ oscillations is precociously interrupted, the incidence of implantation is compromised whereas hyper-stimulation of Ca2+ signaling events compromises post-implantation development. Moreover, although there was no major difference in the overall growth rates of the offspring, those obtained following hyper-stimulation exhibited a far greater variability in their weight. Analysis of global patterns of gene expression by microarray analysis revealed that approximately 20% of the transcripts are mis-regulated when too few oscillations are experienced by the embryo and EASE analysis indicates that genes preferentially involved in RNA processing and polymerase II transcription are differentially affected. In addition, a set of genes involved in cell adhesion is also mis-expressed and could thus be mechanistically linked to the observed reduced implantation. Only about 3% of the transcripts were mis-regulated following hyper-stimulation, and EASE analysis indicates that genes preferentially involved in metabolism are differentially affected. In toto, these results indicate that a range Ca2+ signaling events following fertilization (an excess or reduction) has long-term effects on both gene expression and development to term. Experiment Overall Design: We profiled the global gene expression in the blastocysts by treatment of Ca2+ oscillations, and identified the genes differentially expressed.

Dataset Information

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

Background

Methodology/principal findings

Conclusions/significance

Publications

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

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