Cortical granule matrix disassembly during exocytosis in sea urchin eggs

Carrie J. Merkle, Douglas E. Chandler

Research output: Contribution to journalArticle

7 Scopus citations

Abstract

Cortical granule exocytosis in sea urchins was studied using hyperosmotic and polymer-containing seawater to halt granule matrix dispersal. Addition of Na2SO4-containing seawater (2.5 osmole/kg) to Strongylocentrotus purpuratus eggs 10 to 40 sec after insemination resulted in arrest of the exocytic wave during propagation. EM examination of these eggs revealed that matrix disassembly occurred in distinct stages. In the earliest stage, granule-plasma membrane fusion had occurred, but the matrix remained completely intact. This early stage was observed in hyperosmotic media, either ionic or nonionic, suggesting that matrix hydration is required for disassembly and exocytic pore widening, but not for membrane fusion. Subsequent stages, in which partially disassembled matrices remained within ω-configured pockets, were captured by activating eggs in 30% dextran in seawater. Stability of these intermediates stages required the presence of Ca2+ and Mg2+; in the absence of divalent cations the matrices completely disassembled and the exocytic pockets flattened. Divalent cations appeared to prevent fragmentation of the matrix lamellae. Late stages of matrix disassembly, in which the lamellae fragmented and formed small particles, were inhibited by media of high ionic strength. Hyperosmolality alone, provided by sucrose, was unable to halt these late stages suggesting that water availability does not play an important role once a critical point in matrix dispersal has been reached.

Original languageEnglish (US)
Pages (from-to)429-441
Number of pages13
JournalDevelopmental biology
Volume148
Issue number2
DOIs
StatePublished - Dec 1991

ASJC Scopus subject areas

  • Molecular Biology
  • Developmental Biology
  • Cell Biology

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