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Related Experiment Videos

Ascidian sperm lysin system.

Hitoshi Sawada1

  • 1Department of Biochemistry, Graduate School of Pharmaceutical Sciences, Hokkaido University, Sapporo 060-0812, Japan. hswd@pharm.hokudai.ac.jp

Zoological Science
|May 16, 2002
PubMed
Summary
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Sperm proteases acrosin and spermosin are essential for fertilization in ascidians. A novel extracellular ubiquitin-proteasome system, not trypsin-like proteases, directly degrades the vitelline coat via HrVC70.

Area of Science:

  • Reproductive biology and molecular mechanisms of fertilization.

Background:

  • Sperm penetration of the egg's vitelline coat involves a lytic agent, lysin, typically a protease, but its exact mechanism is poorly understood.
  • Ascidians, like Halocynthia roretzi, are self-sterile, suggesting sperm lysin activation upon recognizing the vitelline coat as non-self.
  • Studying ascidian fertilization provides insights due to readily available gametes and a well-defined self-incompatibility system.

Purpose of the Study:

  • To elucidate the molecular mechanisms of sperm-egg interaction and vitelline coat degradation in ascidians.
  • To identify the specific molecules and systems responsible for lysin activity during fertilization.

Main Methods:

  • Investigated the roles of sperm trypsin-like proteases (acrosin and spermosin) in ascidian fertilization.
  • Analyzed the direct lytic activity against the vitelline coat using proteasome and trypsin-like proteases.

Related Experiment Videos

  • Identified the target component of the vitelline coat and investigated the involvement of ubiquitination.

    • Main Results:

    • Two sperm proteases, acrosin and spermosin, are crucial for fertilization and possess vitelline coat binding motifs.
    • The proteasome, not trypsin-like proteases, exhibits direct lytic activity on the vitelline coat.
    • A 70-kDa vitelline coat component (HrVC70), composed of EGF-like repeats, is the target of the ascidian lysin.
    • An extracellular ubiquitin-proteasome system targeting HrVC70 is essential for ascidian fertilization.

    Conclusions:

    • Ascidian fertilization involves specific sperm proteases (acrosin, spermosin) and a novel extracellular ubiquitin-proteasome system for vitelline coat degradation.
    • The proteasome plays a direct role in lysing the vitelline coat by targeting HrVC70, a process facilitated by ubiquitination.