Echinoderm - Fertilization
Acrosome reaction
Animation courtesy of
David Epel and Chris Patton (Stanford
University), from their Sea Urchin Embryology
web site.
The acrosome reaction is a change in
the sperm that is common to many higher animals. In the sea
urchin, contact with egg jelly initiates
the acrosome reaction, which is a calcium-mediated process.
In response to signals transduced by receptors on the
surface of the sperm that bind to components of egg jelly
(red), actin polymerizes from a pool of globular actin
(pink) to form the acrosomal process. The acrosomal
vesicle (green) fuses with the plasma membrane,
releasing enzymes from the tip of the sperm that aid
digestion of egg jelly. At the same time,
bindin (blue) is deposited on the surface
of the acrosome-reacted sperm.