Scientists at Stanford University in the US have discovered the key ingredient that triggers development in the newly fertilised egg. Their findings, published in the journal Nature last week, could lead to new treatments for male infertility.
The researchers studied egg and sperm from sea urchins, and found that upon contact with the egg, the sperm produces large amounts of nitric oxide gas. This in turn sparks the release of calcium throughout the fertilised egg, which leads to the chemical changes needed to start embryo development. Although scientists have long known that calcium is the essential factor that causes the egg to start dividing, the trigger for the build-up of calcium remained a mystery.
The new study found that a normal sea urchin sperm contains an enzyme called nitric oxide synthase, which remains inactive until a few seconds before fertilisation. 'As the sperm approaches the egg the enzyme quickly produces large amounts of nitric oxide gas, which is injected into the egg once the egg and sperm make contact' says team leader David Edel.
Edel believes that procedures using nitric oxide to treat male infertility could now be developed. 'There are lots of defects in human sperm, and there could well be deficiencies in nitric oxide concentrations in the sperm of some males' he explained. But the scientists must first show that nitric oxide is crucial to successful fertilisation in mammals, as well as sea urchins. If so, the gas may be used to improve the efficiency of mammalian cloning (somatic cell nuclear transfer [SCNT]), says Edel.
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Urchin's clue to male infertility