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Toad egg-jelly as a source of divalent cations essential for fertilization
Developmental Biology
|October 1, 1984
Summary
Toad egg jelly supports fertilization by retaining essential calcium and magnesium ions. Removing the jelly allows fertilization in solutions with these specific divalent cations, revealing the jelly's ion-regulating role.
Area of Science:
- Reproductive Biology
- Developmental Biology
- Cellular Physiology
Background:
- Dejellied toad eggs (Bufo bufo japonicus) are not fertilizable in standard solutions.
- Fertilization is restored when eggs are inseminated in solutions containing egg jelly components.
- The specific components responsible for supporting fertilization remain to be fully defined.
Purpose of the Study:
- To elucidate the fertilization-supporting activity of toad egg jelly.
- To identify the key chemical components within the egg jelly that facilitate fertilization.
- To understand the mechanism by which egg jelly influences sperm-egg interaction.
Main Methods:
- Dejellied toad eggs were inseminated in various solutions, including UV-solubilized jelly (UVJ), its dialyzate (UVJD), heated UVJD (ashes), and reconstituted salt solutions (RSS).
- Individual salt solutions (CaCl2, MgCl2, KCl, NaCl) were tested for their ability to support fertilization.
- The effect of EDTA on fertilization was examined to assess the role of divalent cations.
- Sperm motility was assessed in media with varying cation concentrations.
- Ion content of egg jelly and its behavior during dialysis and gel filtration were analyzed.
Main Results:
- Dejellied eggs were fertilized in UVJ, UVJD, ashes of UVJD, and RSS mimicking UVJD's ionic composition.
- Fertilization was successful in media containing 1-5 mM CaCl2 and/or MgCl2, but not NaCl; KCl showed minimal support.
- The fertilization-supporting activity of UVJD was lost upon chelation of divalent cations with EDTA, indicating their crucial role.
- Egg jelly retains significant amounts of Ca2+ and Mg2+, which are released upon immersion in water, enabling fertilization.
Conclusions:
- Toad egg jelly facilitates fertilization primarily by retaining essential divalent cations (Ca2+ and Mg2+) around the egg.
- Fertilization of dejellied eggs is achievable in a simple salt solution containing 2-5 mM Ca2+ or Mg2+.
- The egg jelly acts as an ion reservoir, maintaining optimal ionic conditions for sperm penetration.