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Characterizing the role of extracellular zinc in the slow block to polyspermy for the African clawed frog

Milnes, Beatrice (2022) Characterizing the role of extracellular zinc in the slow block to polyspermy for the African clawed frog. Undergraduate Thesis, University of Pittsburgh. (Unpublished)

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Fertilization of an egg by multiple sperm, a condition referred to as polyspermy, is lethal for developing embryos from nearly all sexually reproducing animals. In response, various mechanisms known as polyspermy blocks have evolved to prevent supernumerary fertilizations and the developmental problems resulting from fertilization of an egg by more than one sperm. One of the egg-based polyspermy blocks involves the release of cortical granules docked at the egg’s plasma membrane, into the extracellular milieu, a process known as the slow block to polyspermy. During the slow block, eggs from diverse animals release zinc ions, and this extracellular zinc is hypothesized to contribute to the mechanism that keeps sperm out of fertilized eggs. This hypothesis is supported by the finding that insemination of eggs from diverse species in concentrations of zinc similar to the amount released during the slow block, prevents fertilization and the initiation of embryonic development. Using fertilization in the African clawed frog Xenopus laevis, I have demonstrated that treatment of both eggs and sperm with zinc prior to insemination was sufficient to stop fertilization. Using the cell-impermeant zinc chelator ZX1, I have shown that the zinc block of fertilization is reversible in both gametes, consistent with a role for extracellular zinc in preventing fertilization. Further, I demonstrated that the zinc induced infertility phenotype of gametes can extend to other transition metals. This data indicates that extracellular zinc may target both sperm and eggs, suggesting that the classic belief that the slow block to polyspermy only changes the egg may not provide a complete picture of how multiple sperm are kept out of the nascent zygote. Understanding how zinc blocks polyspermy could have implications in optimizing clinical conditions used for in vitro fertilizations in humans.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Milnes, Beatriceblm131@pitt.edublm131
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairCarlson, Anne E.acarlson@pitt.eduacarlson
Committee MemberHildebrand, Jeffrey D.jeffh@pitt.edujeffh
Committee MemberKiselyov, Kirillkiselyov@pitt.edukiselyov
Committee MemberPuljung, Michael
Date: 26 April 2022
Date Type: Publication
Defense Date: 11 April 2022
Approval Date: 26 April 2022
Submission Date: 22 April 2022
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Number of Pages: 40
Institution: University of Pittsburgh
Schools and Programs: David C. Frederick Honors College
Dietrich School of Arts and Sciences > Biological Sciences
Degree: BPhil - Bachelor of Philosophy
Thesis Type: Undergraduate Thesis
Refereed: Yes
Uncontrolled Keywords: zinc, fertilization, polyspermy, slow block
Date Deposited: 26 Apr 2022 11:18
Last Modified: 26 Apr 2022 11:18


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