NSF PR 95-51 - August 10, 1995
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Early Events Revealed in the Fertilization of an Egg by a Sperm
For the first time, a detailed picture is emerging
of the molecular events that occur during fertilization
of an egg by a sperm. David Stout, a National Science
Foundationsupported researcher at the Scripps Research
Institute in La Jolla, California, and Victor Vacquier,
a scientist at the University of California, San Diego,
present results of their work on this process in the
cover article of the September issue of the Journal
of Cell Biology.
The organism they have studied is the California red
abalone, Haliotis rufescens. In order for a sperm
to fuse with an egg, it must first penetrate the egg's
extracellular membrane. The abalone sperm uses a protein
called lysin to create a hole in this membrane, through
which the sperm passes.
Abalone are marine mollusks, with eight species inhabiting
the west coast of North America. The species have
overlapping breeding seasons and habitats, yet maintain
themselves as distinct. The specific structure of
lysin is responsible for the species-selective recognition.
Stout and Vacquier have determined the three- dimensional
molecular structure of lysin. They have shown that
two molecules of lysin associate to form a dimer (a
protein made up of two polypeptide chains paired together),
and have also determined the structure of this dimer.
Addition of egg extracellular membrane causes the
lysin dimer to dissociate into two monomers. The lysin
monomer then penetrates the membrane and creates a
hole through which sperm passes. Specific functions
can now be assigned to specific features of the lysin
molecule that stabilize the dimer and allow the monomer
to interact with the extracellular membrane. "These
experiments," says Stout, "will allow cell biologists
to visualize and understand the fundamentally important
biological process of fertilization." The research
is funded by NSF's division of molecular and cellular
biosciences.
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