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PtdIns(4,5)P₂ dynamics at fertilization

Fertilization of mammalian eggs triggers a series of sustained intracellular Ca²⁺ oscillations required for resumption of meiosis and exocytosis of cortical granules. The release of Ca²⁺ from intracellular stores is a consequence of phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P₂] turnover. One might therefore expect to see reduced levels of plasma membrane PtdIns(4,5)P₂ after fertilization. Instead, it seems that they go up (see p. 2139). Guillaume Halet and co-workers have used GFP fusion proteins containing a pleckstrin-homology domain that binds to PtdIns(4,5)P₂ to monitor its dynamics in eggs. They find that fertilization produces a net increase in PtdIns(4,5)P₂ levels around the vegetal pole after the initial rise in Ca²⁺ concentration. This increase can be blocked by Ca²⁺ buffers and specific inhibitors of Ca²⁺-dependent exocytosis. In addition, it can be blocked by 30 µM wortmannin (which inhibits PtdIns(4,5)P₂ synthesis) but not 100 nM wortmannin (which inhibit PI 3-kinase). Carroll and co-workers therefore propose that fertilization increases PtdIns(4,5)P₂ levels through Ca²⁺-dependent cortical granule exocytosis. This could supply substrate/enzymes for synthesis of PtdIns(4,5)P₂, which might participate in membrane retrieval or actin remodelling after exocytosis.

Related articles in JCS:

The dynamics of plasma membrane PtdIns(4,5)P₂ at fertilization of mouse eggs

Guillaume Halet, Richard Tunwell, Tamas Balla, Karl Swann, and John Carroll
JCS 2002 115: 2139-2149. [Abstract] [Full Text]  

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This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Related articles in JCS Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Search for Related Content