A cytosolic sperm protein factor mobilizes Ca2+ from intracellular stores by activating multiple Ca2+ release mechanisms independently of low molecular weight messengers.
Ca2+ oscillations can be induced in mammalian eggs and somatic cells by microinjection of a cytosolic sperm protein factor. The nature of the sperm factor-induced Ca2+ signaling was investigated by adding sperm protein extracts to homogenates of sea urchin eggs, which contain multiple classes of Ca2+ release mechanisms. We show that the sperm factor mobilizes Ca2+ from non-mitochondrial Ca2+ stores in egg homogenates after a distinct latency. This latency is abolished by preincubation of sperm extracts with egg cytosol. The preincubation step is highly temperature-dependent and generates a high molecular weight, protein-based Ca2+-releasing agent that can also mobilize Ca2+ from purified egg microsomes. This Ca2+ release appears to be mediated via both inositol 1,4,5-trisphosphate and ryanodine receptors, since homologous desensitization of these two release mechanisms by their respective agonists inhibits further release by the sperm factor. However, sperm factor-induced Ca2+ release by these channels is independent of inositol 1,4, 5-trisphosphate or cADPR since antagonists of either of these two messengers did not block the Ca2+ release effected by the sperm factor. The sperm protein factor may cause Ca2+ release via an enzymatic step that generates a protein-based Ca2+-releasing agent.
Galione
A
A
University Department of Pharmacology, Oxford University, Mansfield Road, Oxford OX1 3QT, United Kingdom. antony.galione@pharm.ox.ac.uk
Jones
K T
KT
Lai
F A
FA
Swann
K
K
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism*; D017136:Ion Transport; D008297:Male; D008970:Molecular Weight; D012617:Sea Urchins; D013094:Spermatozoa / Q000378:metabolism*; D013552:Swine
D015220:Calcium Channels; D002352:Carrier Proteins; D002118:Calcium