#cortical granules

Regeneration -ll

Cortical granules are homologous to:

Cortical granules are membrane-bound dense core secretory organelles positioned beneath egg plasma membrane, synthesized during oocyte growth via Golgi cisternae producing condensing vacuoles loaded with proteases, ovoperoxidase, hyaline, and sulfated glycosaminoglycans. Their biogenesis, acidic pH, lysosomal hydrolase content, and calcium-triggered SNARE-mediated exocytosis parallel sperm acrosomal vesicles, making them egg equivalents of acrosomes. Both belong to regulated secretory lysosome lineage bearing mannose-6-phosphate receptors. Ribosomes perform translation, nuclei contain chromosomes, and other organelles lack regulated exocytosis machinery, explaining why cortical granules are considered homologous to acrosomal vesicles rather than housekeeping organelles.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 7: Cortical granules as egg acrosome equivalents - Golgi-derived secretory vesicles.

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Sea urchin -l

Cortical granules are homologous to:

Cortical granules are dense membrane-bound vesicles arranged in monolayer underlying egg plasma membrane, stockpiled with proteases, peroxidase, glycosaminoglycans and structural proteins destined for rapid Ca2+-triggered exocytosis at fertilization. Detailed ultrastructural and biochemical comparison demonstrates striking homology with acrosomal vesicles of spermatozoa – both derive from Golgi apparatus in their respective gametes, contain hydrolytic enzymes, and undergo regulated SNARE-mediated exocytosis releasing contents to modify extracellular coats. Functionally, cortical reaction transforms vitelline layer similarly to how acrosomal reaction exposes bindin. They are not ribosomes, nuclei or lysosomes although enzymatically similar. Homology reflects shared evolutionary origin of secretory vesicles.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 7: Cortical granules and acrosome vesicle homology.

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Sea urchin -lll

Removal of cortical granules prevents:

Cortical granules lie beneath egg plasma membrane and upon calcium rise fuse releasing contents that transform vitelline membrane into fertilization envelope constituting slow, permanent block to polyspermy. If granules are removed by mild centrifugation that stratifies them away or exocytosis blocked by inhibitors, envelope elevation fails despite normal sperm fusion. Fast electrical block still occurs but membrane repolarizes within minute, allowing supernumerary sperm to fuse causing polyspermy, multipolar mitoses, and lethal aneuploidy. Therefore granule removal prevents polyspermy prevention, while sperm attraction, entry, and cleavage initiation can still initially occur until developmental defects manifest and embryo arrests.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 7: Cortical granule removal prevents polyspermy slow block.

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Sea urchin -lll

Cortical granules convert:

Unfertilized sea urchin egg vitelline membrane lies closely apposed to plasma membrane with little perivitelline space. Upon calcium-dependent cortical granule exocytosis, contents including hyalin, proteases, sulfated mucopolysaccharides, and ovoperoxidase are released. Proteases cleave linkers between vitelline membrane and plasma membrane, osmotic swelling by glycosaminoglycans elevates membrane outward, and cross-linking enzymes harden it via di-tyrosine bonds. Modified vitelline membrane becomes fertilization envelope raised above egg surface with perivitelline space between. This conversion changes soft vitelline layer into tough barrier preventing supernumerary sperm entry and protecting embryo before hatching occurs.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 7: Cortical granules convert vitelline membrane to fertilization envelope.

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