|
Summary of Research Projects (Supports in 2003
Fiscal Year)
| Subjects |
Studies on the Mechanism of Ascidian Fertilization |
| Representative researcher |
Nagoya University Hitoshi SAWADA |
| Joint researcher |
Nagoya University Yoshito HARADA |
| Fertilization is a precisely
controlled process involving many gamete molecules in sperm
binding to and penetration through the extracellular matrix
of the egg. We have been studying the fertilization mechanism
in ascidians, because we can obtain large quantities of gametes,
which are readily fertilized in the laboratory. Whereas ascidians
are hermaphrodites, many ascidians are strictly self-sterile.
Therefore, after sperm recognize the vitelline coat as nonself,
the sperm lysin system seems to be activated. We revealed
that two sperm trypsin-like proteases, acrosin and spermosin,
and the proteasome are essential for fertilization in H.
roretzi. We found that the proteasome rather than trypsin-like
proteases has a direct lytic activity toward the vitelline
coat. The target for the lysin was found to be a 70-kDa vitelline-coat
component called HrVC70, which is made up of 12 EGF-like
repeats. In addition to the proteasome, the ubiquitination
system toward the HrVC70 was found to be necessary for ascidian
fertilization. In this report, I describe recent progress
on the novel extracellular ubiquitin-proteasome system, which
plays an essential role in the degradation of the vitelline
coat, and also the self/nonself-recognition mechanism during
fertilization. |
|
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