A century-old mystery about sex finally appears to have been solved by a Stanford-led team of researchers.
Their discovery, reported in the journal Nature, could have wide-ranging implications for genetic research and the treatment of infertility.
The study focuses on the ultimate goal of sex - fertilization.
When a sperm and an egg come together, something triggers the cascade of chemical events that eventually results in the development of an embryo.
'Since the turn of the century, people have wondered exactly how sperm-egg contact initiates development,' says biologist David Epel.
The answer, he says, begins with the build-up of nitric oxide gas inside the sperm.
Epel and his colleagues describe their discovery in the Aug. 10 issue of Nature.
Their research is based on the sex lives of male and female sea urchins - spiny, purple invertebrates found in the Pacific Ocean just a few yards from Epel's laboratory at Stanford`s Hopkins Marine Station on California's Monterey Bay.
Their experiments reveal that normal sea urchin sperm contains an enzyme called nitric oxide synthase, which remains inactive until a few seconds before fertilization.
'As the sperm approaches the egg,' notes Epel, 'the enzyme quickly produces large amounts of nitric oxide gas, which is injected into the egg once the sperm and the egg make contact.'
The injection of nitric oxide gas from the sperm triggers the release of calcium inside the egg about 30 seconds later.
Calcium then activates nitric oxide synthase already present in the egg, producing more nitric oxide gas, which in turn causes the release of more calcium throughout the egg.
In the 1970s, Epel and other researchers showed that calcium is the essential factor that sparks development in eggs. As calcium levels rise, metabolic changes occur that cause the egg to divide and form into an embryo.
But what actually triggers the build-up of calcium
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Contact: Mark Shwartz
mshwartz@stanford.edu
650-723-9296
Stanford University
9-Aug-2000