Calcium release at fertilization in starfish eggs is mediated by phospholipase Cgamma.
Although inositol trisphosphate (IP3) functions in releasing Ca2+ in eggs at fertilization, it is not known how fertilization activates the phospholipase C that produces IP3. To distinguish between a role for PLCgamma, which is activated when its two src homology-2 (SH2) domains bind to an activated tyrosine kinase, and PLCbeta, which is activated by a G protein, we injected starfish eggs with a PLCgamma SH2 domain fusion protein that inhibits activation of PLCgamma. In these eggs, Ca2+ release at fertilization was delayed, or with a high concentration of protein and a low concentration of sperm, completely inhibited. The PLCgammaSH2 protein is a specific inhibitor of PLCgamma in the egg, since it did not inhibit PLCbeta activation of Ca2+ release initiated by the serotonin 2c receptor, or activation of Ca2+ release by IP3 injection. Furthermore, injection of a PLCgamma SH2 domain protein mutated at its phosphotyrosine binding site, or the SH2 domains of another protein (the phosphatase SHP2), did not inhibit Ca2+ release at fertilization. These results indicate that during fertilization of starfish eggs, activation of phospholipase Cgamma by an SH2 domain-mediated process stimulates the production of IP3 that causes intracellular Ca2+ release.
Carroll
D J
DJ
Department of Physiology, University of Connecticut Health Center, Farmington, Connecticut 06032, USA. carroll@lifesci.lscf.ucsb.edu
Ramarao
C S
CS
Mehlmann
L M
LM
Roche
S
S
Terasaki
M
M
Jaffe
L A
LA
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D005260:Female; D005982:Glutathione Transferase / Q000737:chemistry / Q000494:pharmacology; D007527:Isoenzymes / Q000378:metabolism*; D008297:Male; D008845:Microinjections; D009865:Oocytes / Q000166:cytology / Q000201:enzymology; D051966:Phospholipase C gamma; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D012680:Sensitivity and Specificity; D015398:Signal Transduction / Q000502:physiology; D013084:Sperm-Ovum Interactions / Q000502:physiology*; D013215:Starfish / Q000502:physiology*; D010738:Type C Phospholipases / Q000378:metabolism*; D018909:src Homology Domains / Q000502:physiology
D007527:Isoenzymes; D011993:Recombinant Fusion Proteins; D005982:Glutathione Transferase; D010738:Type C Phospholipases; D051966:Phospholipase C gamma; D002118:Calcium