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Protein tyrosine kinase‐dependent release of intracellular calcium in the sea urchin egg
Author(s) -
Shen Sheldon S.,
Kinsey William H.,
Lee ShyhJye
Publication year - 1999
Publication title -
development, growth and differentiation
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.864
H-Index - 66
eISSN - 1440-169X
pISSN - 0012-1592
DOI - 10.1046/j.1440-169x.1999.413436.x
Subject(s) - sea urchin , microbiology and biotechnology , tyrosine kinase , calcium in biology , intracellular , chemistry , calcium , biology , signal transduction , organic chemistry
The aminoguanide, methylglyoxal bis(guanylhydrazone) (MGBG), was shown to stimulate phosphorylation of RR‐SRC, a synthetic protein tyrosine kinase (PTK) substrate, and different levels of tyrosyl phosphorylation of endogenous proteins in a sea urchin egg membrane‐cortex preparation. Stimulating protein tyrosine kinase activity in the sea urchin egg stimulated intracellular Ca 2+ release, because microinjection of 1–5 mM of MGBG into unfertilized eggs triggered a transient rise in intracellular Ca 2+ activity ([Ca 2+ ] i ) after a brief latent period. Pretreating eggs with PTK‐specific inhibitors, genistein or tyrphostin B42+, significantly inhibited the MGBG‐induced rise in [Ca 2+ ] i . Methylglyoxal bis(guanylhydrazone) stimulation of PTK activities in the unfertilized sea urchin egg appeared to trigger Ca 2+ release through phospholipase C (PLC)‐dependent inositol 1,4,5‐trisphosphate (InsP 3 ) production. The MGBG‐induced Ca 2+ response could be suppressed in eggs preloaded with the InsP 3 receptor antagonist, heparin, and was reduced in eggs pretreated with U7312+, a PLC inhibitor. However, the response was unchanged in eggs treated with nicotinamide, an inhibitor of ADP‐ribosyl cyclase, or nifedipine, an inhibitor of nicotinic acid adenine dinucleotide phosphate activity. These results suggest that MGBG may be useful as a chemical agonist of PTK in sea urchin eggs and allow direct testing of the PTK requirement for the transient rise in [Ca 2+ ] i in sea urchin eggs during fertilization. Although genistein was observed to significantly delay the onset, the sperm‐induced Ca 2+ response in PTK inhibitor‐loaded eggs otherwise appeared normal. Therefore, it was concluded that sea urchin eggs contain a PTK‐dependent pathway that can mediate intracellular Ca 2+ release, but PTK activity does not appear to be required for the fertilization response.