Different Ca2+-releasing abilities of sperm extracts compared with tissue extracts and phospholipase C isoforms in sea urchin egg homogenate and mouse eggs.
A soluble phospholipase C (PLC) from boar sperm generates InsP(3) and hence causes Ca(2+) release when added to sea urchin egg homogenate. This PLC activity is associated with the ability of sperm extracts to cause Ca(2+) oscillations in mammalian eggs following fractionation. A sperm PLC may, therefore, be responsible for causing the observed Ca(2+) oscillations at fertilization. In the present study we have further characterized this boar sperm PLC activity using sea urchin egg homogenate. Consistent with a sperm PLC acting on egg PtdIns(4,5)P(2), the ability of sperm extracts to release Ca(2+) was blocked by preincubation with the PLC inhibitor U73122 or by the addition of neomycin to the homogenate. The Ca(2+)-releasing activity was also detectable in sperm from other species and in whole testis extracts. However, activity was not observed in extracts from other tissues. Moreover recombinant PLCbeta1, -gamma1, -gamma2, -delta1, all of which had higher specific activities than boar sperm extracts, were not able to release Ca(2+) in the sea urchin egg homogenate. In addition these PLCs were not able to cause Ca(2+) oscillations following microinjection into mouse eggs. These results imply that the sperm PLC possesses distinct properties that allow it to hydrolyse PtdIns(4,5)P(2) in eggs.
Jones
K T
KT
Department of Anatomy, University College, Gower Street, London, WC1E 6BT, UK. k.t.jones@ncl.ac.uk
Matsuda
M
M
Parrington
J
J
Katan
M
M
Swann
K
K
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007527:Isoenzymes / Q000378:metabolism*; D008297:Male; D051379:Mice; D010063:Ovum / Q000201:enzymology*; D012617:Sea Urchins; D015398:Signal Transduction / Q000187:drug effects; D013094:Spermatozoa / Q000201:enzymology / Q000378:metabolism*; D013552:Swine; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors / Q000378:metabolism*
D004791:Enzyme Inhibitors; D007527:Isoenzymes; D010738:Type C Phospholipases; D002118:Calcium