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Extracellular Ca2+ Is Required for Fertilization in the African Clawed Frog, Xenopus laevis

Klymkowsky, Michael and Wozniak, Katherine L. and Mayfield, Brianna L. and Duray, Alexis M. and Tembo, Maiwase and Beleny, David O. and Napolitano, Marc A. and Sauer, Monica L. and Wisner, Bennett W. and Carlson, Anne E. (2017) Extracellular Ca2+ Is Required for Fertilization in the African Clawed Frog, Xenopus laevis. PLOS ONE, 12 (1). e0170405. ISSN 1932-6203

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The necessity of extracellular Ca2+ for fertilization and early embryonic development in the African clawed frog, Xenopus laevis, is controversial. Ca2+ entry into X. laevis sperm is reportedly required for the acrosome reaction, yet fertilization and embryonic development have been documented to occur in high concentrations of the Ca2+ chelator BAPTA. Here we sought to resolve this controversy.Using the appearance of cleavage furrows as an indicator of embryonic development, we found that X. laevis eggs inseminated in a solution lacking added divalent cations developed normally. By contrast, eggs inseminated in millimolar concentrations of BAPTA or EGTA failed to develop. Transferring embryos to varying solutions after sperm addition, we found that extracellular Ca2+ is specifically required for events occurring within the first 30 minutes after sperm addition, but not after. We found that the fluorescently stained sperm were not able to penetrate the envelope of eggs inseminated in high BAPTA, whereas several had penetrated the vitelline envelope of eggs inseminated without a Ca2+ chelator, or with BAPTA and saturating CaCl2. Together these results indicate that fertilization does not occur in high concentrations of Ca2+ chelators. Finally, we found that the jelly coat includes >5 mM of readily diffusible Ca2+.Taken together, these data are consistent with requirement of extracellular Ca2+ for fertilization. Based on our findings, we hypothesize that the jelly coat surrounding the egg acts as a reserve of readily available Ca2+ ions to foster fertilization in changing extracellular milieu.


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Item Type: Article
Status: Published
CreatorsEmailPitt UsernameORCID
Klymkowsky, Michael
Wozniak, Katherine L.
Mayfield, Brianna L.
Duray, Alexis
Tembo, Maiwase
Beleny, David O.
Napolitano, Marc A.
Sauer, Monica L.
Wisner, Bennett W.
Carlson, Anne
Date: 23 January 2017
Date Type: Publication
Journal or Publication Title: PLOS ONE
Volume: 12
Number: 1
Publisher: Public Library of Science (PLoS)
Page Range: e0170405
DOI or Unique Handle: 10.1371/journal.pone.0170405
Schools and Programs: Dietrich School of Arts and Sciences > Biological Sciences
Refereed: Yes
ISSN: 1932-6203
Official URL:
Article Type: Research Article
Date Deposited: 08 Jun 2020 13:08
Last Modified: 08 Jun 2020 13:08


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