Phosphoinositide metabolism at fertilization of sea urchin eggs measured with a GFP-probe.
Fertilization elicits a dramatic, transient rise in Ca2+ within the egg which is an essential component of egg activation and consequent initiation of development. In the sea urchin egg, three distinct Ca2+ stores have been identified which could, either individually or in combination, initiate Ca2+ release at fertilization. Inositol 1,4,5-trisphosphate (IP3) production by phospholipase C (PLC) has been suggested as the singular signal in initiating the Ca2+ transient. Other studies indicate that Ca2+ stores gated by cyclic adenosine diphosphate ribose (cADPR) or nicotinic acid adenine dinucleotide phosphate (NAADP) are also necessary. We have examined the temporal relationship between the Ca2+ rise and IP3 production at fertilization in vivo within individual eggs using a green fluorescent protein (GFP) coupled to a pleckstrin homology (PH) domain that can detect changes in IP3. Translocation of the probe occurred after the Ca2+ rise was initiated. Earlier, and possibly smaller, IP3 changes could not be excluded due to limitations in probe sensitivity. High IP3 levels are maintained during the decline in cytoplasmic Ca2+, suggesting that later IP3 metabolism might not be related to regulation of Ca2+, but may function to modulate other PIP2 regulated events such as actin polymerization or reflect other novel phosphoinositide signaling pathways.
Thaler
Catherine D
CD
Hopkins Marine Station, Stanford University, Pacific Grove, CA 93950, USA.
Kuo
Richard C
RC
Patton
Chris
C
Preston
Christina M
CM
Yagisawa
Hitoshi
H
Epel
David
D
D000818:Animals; D001483:Base Sequence; D002118:Calcium / Q000378:metabolism; D036563:Cyclic ADP-Ribose / Q000378:metabolism; D017931:DNA Primers; D049452:Green Fluorescent Proteins / Q000378:metabolism*; D015544:Inositol 1,4,5-Trisphosphate / Q000096:biosynthesis; D047331:Lytechinus / Q000502:physiology*; D015335:Molecular Probes; D009249:NADP / Q000031:analogs & derivatives* / Q000378:metabolism; D010063:Ovum / Q000378:metabolism*; D010716:Phosphatidylinositols / Q000378:metabolism*; D010738:Type C Phospholipases / Q000378:metabolism
D017931:DNA Primers; D015335:Molecular Probes; D010716:Phosphatidylinositols; D036563:Cyclic ADP-Ribose; D049452:Green Fluorescent Proteins; D009249:NADP; C024376:NAADP; D015544:Inositol 1,4,5-Trisphosphate; D010738:Type C Phospholipases; D002118:Calcium