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Cortical granule exocytosis is triggered by different thresholds of calcium during fertilisation in sea urchin eggs.

Publication ,  Journal Article
Matese, JC; McClay, DR
Published in: Zygote (Cambridge, England)
February 1998

In sea urchin eggs, fertilisation is followed by a calcium wave, cortical granule exocytosis and fertilisation envelope elevation. Both the calcium wave and cortical granule exocytosis sweep across the egg in a wave initiated at the point of sperm entry. Using differential interference contrast (DIC) microscopy combined with laser scanning confocal microscopy, populations of cortical granules undergoing calcium-induced exocytosis were observed in living urchin eggs. Calcium imaging using the indicator Calcium Green-dextran was combined with an image subtraction technique for visual isolation of individual exocytotic events. Relative fluorescence levels of the calcium indicator during the fertilisation wave were compared with cortical fusion events. In localised regions of the egg, there is a 6s delay between the detection of calcium release and fusion of cortical granules. The rate of calcium accumulation was altered experimentally to ask whether this delay was necessary to achieve a threshold concentration of calcium to trigger fusion, or was a time-dependent activation of the cortical granule fusion apparatus after the 'triggering' event. Calcium release rate was attenuated by blocking inositol 1,4,5-triphospate (InsP3)-gated channels with heparin. Heparin extended the time necessary to achieve a minimum concentration of calcium at the sites of cortical granule exocytosis. The data are consistent with the conclusion that much of the delay observed normally is necessary to reach threshold concentration of calcium. Cortical granules then fuse with the plasma membrane. Further, once the minimum threshold calcium concentration is reached, cortical granule fusion with the plasma membrane occurs in a pattern suggesting that cortical granules are non-uniform in their calcium sensitivity threshold.

Duke Scholars

Published In

Zygote (Cambridge, England)

DOI

EISSN

1469-8730

ISSN

0967-1994

Publication Date

February 1998

Volume

6

Issue

1

Start / End Page

55 / 65a

Related Subject Headings

  • Subtraction Technique
  • Stochastic Processes
  • Second Messenger Systems
  • Sea Urchins
  • Obstetrics & Reproductive Medicine
  • Microscopy, Confocal
  • Membrane Fusion
  • Male
  • Inositol 1,4,5-Trisphosphate
  • Image Processing, Computer-Assisted
 

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Matese, J. C., & McClay, D. R. (1998). Cortical granule exocytosis is triggered by different thresholds of calcium during fertilisation in sea urchin eggs. Zygote (Cambridge, England), 6(1), 55-65a. https://doi.org/10.1017/s0967199400005086
Matese, J. C., and D. R. McClay. “Cortical granule exocytosis is triggered by different thresholds of calcium during fertilisation in sea urchin eggs.Zygote (Cambridge, England) 6, no. 1 (February 1998): 55-65a. https://doi.org/10.1017/s0967199400005086.
Matese, J. C., and D. R. McClay. “Cortical granule exocytosis is triggered by different thresholds of calcium during fertilisation in sea urchin eggs.Zygote (Cambridge, England), vol. 6, no. 1, Feb. 1998, pp. 55-65a. Epmc, doi:10.1017/s0967199400005086.
Journal cover image

Published In

Zygote (Cambridge, England)

DOI

EISSN

1469-8730

ISSN

0967-1994

Publication Date

February 1998

Volume

6

Issue

1

Start / End Page

55 / 65a

Related Subject Headings

  • Subtraction Technique
  • Stochastic Processes
  • Second Messenger Systems
  • Sea Urchins
  • Obstetrics & Reproductive Medicine
  • Microscopy, Confocal
  • Membrane Fusion
  • Male
  • Inositol 1,4,5-Trisphosphate
  • Image Processing, Computer-Assisted