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Experiments Pertaining to the Suppression of Accessory Sperm in Fertilized Newt Eggs*: (polyspermy/cleavage/sperm

Yasuhiro Iwao1, Hisashi Yamasaki1, Chiaki Katagiri2

  • 1Department of Biology, Faculty of Science, Yamaguchi University, Yamaguchi 753, Japan.

Development, Growth & Differentiation
|June 7, 2023
PubMed

Insights

Accessory sperm in newt eggs form pronuclei but degenerate. The zygote nucleus inhibits accessory sperm participation in cleavage, likely by suppressing centriolar replication, preventing proper cell division.

Area of Science:

  • Developmental biology
  • Cell biology
  • Reproductive biology

Background:

  • Newt eggs (Cynops pyrrhogaster) are polyspermic, meaning multiple sperm fertilize a single egg.
  • Accessory sperm in these eggs initiate pronuclear formation and DNA synthesis but typically degenerate.
  • The fate of these accessory sperm and their role in early development is not fully understood.

Purpose of the Study:

  • To investigate the factors controlling the fate of accessory sperm in polyspermic newt eggs.
  • To determine the influence of the zygote nucleus on accessory sperm behavior and cleavage.
  • To elucidate the mechanisms underlying the suppression of accessory sperm during early embryonic development.

Main Methods:

  • Micromanipulation of fertilized newt eggs, including bisection to create merogons.
  • Inhibition of nuclear events using cycloheximide and DNA synthesis using aphidicolin.
  • Cytological examination of nuclear and cytoplasmic events during early cleavage stages.

Main Results:

  • Andromerogons (egg halves containing sperm pronuclei) cleaved frequently when produced before zygote nucleus formation, but not after.
  • Accessory sperm failed to participate in cleavage when separated from the diploid merogon by a high cytoplasmic bridge.
  • Removal of the egg nucleus or inhibition of early nuclear events induced multipolar cleavage.
  • Absence of DNA synthesis led to abortive first cytokinesis and failure of subsequent divisions.
  • Suppression of accessory sperm appears linked to zygote nucleus-mediated inhibition of centriolar replication.

Conclusions:

  • The zygote nucleus plays a critical role in regulating the fate of accessory sperm in polyspermic newt eggs.
  • Inhibition of centriolar replication by the zygote nucleus is a key mechanism preventing accessory sperm participation in cleavage.
  • Proper cell cycle progression and DNA synthesis are essential for successful cytokinesis and embryonic development.

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