#IP3

Regeneration -ll

IP3 in fertilization is generated by:

Phosphoinositide signaling during egg activation begins with hydrolysis of phosphatidylinositol 4,5-bisphosphate PIP2 residing in inner leaflet of plasma membrane. Enzyme catalyzing cleavage is phospholipase C activated via sperm-derived PLCzeta or Src kinase-mediated phosphorylation of PLCgamma after gamete fusion. Cleavage yields membrane-retained diacylglycerol activating protein kinase C and soluble inositol trisphosphate IP3 diffusing to endoplasmic reticulum triggering calcium release. Protein kinase C is downstream target not producer of IP3, dynein ATPase powers axonemal motility, Na+/H+ exchanger regulates pH independent of phosphoinositide turnover, making PLC sole generator of IP3 surge at fertilization.

Ref: NCBI Bookshelf, Cell Signaling, Chapter 9: Phospholipase C cleavage of PIP2 to generate IP3 and DAG.

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Sea urchin -l

IP3 in fertilization is generated by:

Fertilization induces phosphoinositide signaling cascade generating crucial second messenger IP3. Phospholipase C isoforms, including sperm-contributed PLCζ and egg PLCγ activated by Src family tyrosine kinases downstream of sperm-receptor interaction, hydrolyze phosphatidylinositol 4,5-bisphosphate abundant in inner leaflet of plasma membrane. Cleavage yields membrane-retained diacylglycerol that activates protein kinase C and soluble inositol 1,4,5-trisphosphate that diffuses to endoplasmic reticulum. IP3 generation absolutely requires phospholipase C enzymatic catalysis; without PLC activity calcium wave fails. Protein kinase C, dynein ATPase and Na+/H+ exchanger act downstream modulating pH, cytoskeleton and motility but are not synthesizing IP3 upstream.

Ref: Carroll et al., Dev Biol 1997, Phospholipase C and IP3 generation at fertilization; Alberts Chapter 15.

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Sea urchin -lll

IP3 initially forms at:

IP3 production begins locally where sperm fuses with egg membrane. Src kinase activated at fusion site phosphorylates PLC-gamma anchored near plasma membrane, triggering rapid hydrolysis of PIP2 precisely at entry cortex. Using fluorescent pleckstrin homology domain sensors, investigators observe PIP2 depletion at sperm entry point first. IP3 then diffuses inward toward ER rich in IP3 receptors, initiating calcium release first near entry and propagating as wave across egg via calcium-induced calcium release. Animal or vegetal pole initiation does not occur unless sperm fuses there. Nuclear production would be too distant for rapid wave initiation across large egg.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 7: IP3 forms at sperm entry site calcium wave.

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Cell Signaling GPCR Pathways - I

PLCβ hydrolyzes PIP2 to generate

IP3 and DAG, is consistent with established principles of cell signaling, receptor pharmacology and cellular regulation. Experimental measurements of binding parameters, genetic loss-of-function studies and pharmacological interventions all converge on the same interpretation. Related options address neighboring concepts but do not satisfy the precise criterion stated in the question.

Ref: NCERT Biology Class 11–12 Alberts et al Molecular Biology of the Cell Lodish et al, Molecular Cell Biology Cooper & Hausman, The Cell Abbas et al., Cellular and Molecular Immunology (for immunology sections)

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Cell Signaling GPCR Pathways - I

IP3 primarily causes release of Ca2+ from

Inositol 1,4,5-trisphosphate generated by phospholipase C diffuses through the cytosol and binds IP3-gated calcium channels on the endoplasmic reticulum. Channel opening releases stored Ca2+ into the cytosol, producing a rapid rise in free calcium that activates calmodulin-dependent enzymes and other calcium-sensitive effectors. The endoplasmic reticulum is therefore the primary source of IP3-mobilized calcium.

Ref: NCERT Biology Class 11–12 Alberts et al Molecular Biology of the Cell Lodish et al, Molecular Cell Biology Cooper & Hausman, The Cell Abbas et al., Cellular and Molecular Immunology (for immunology sections)

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