A unique protein that only occurs in sperm could be the key to a new contraceptive for both
the sexes.The protein, named CatSper, is an ion channel protein that controls the flow of
calcium into sperm tails. Calcium is crucial in enabling sperm to swim, so a drug designed to
block the channel would immobilise sperm and prevent fertilisation.
The discovery is reported by Dr David Clapham, from the Howard Hughes Medical Institute,
and colleagues from Harvard Medical School."This is the only protein I've ever seen that
localises to only one tissue," said Dr Clapham. "We looked carefully through at least fifty
human tissues, and the only place it turned up was in the testes."
"Futhermore, the only place it turned up within the testes was in sperm. And within sperm, it
is found only in the principal piece of the tail." It is also specific to mature sperm and does
not appear to be expressed in sperm precursor cells, or in immature sperm.The very
specific role of the protein means that a contraceptive designed to disrupt it would have far
fewer side effects than a hormone-based contraceptive. Hormones are found in many
Working with mice, the researchers discovered that the sperm of mice without the CatSper
gene were unable to penetrate the outer covering of the egg, the zona pellucida. But when
the researchers mixed the sperm with eggs that had the covering removed, they fertilised
A contraceptive designed to prevent fertilisation would not interfere with the gene but simply
inhibit the ion channel protein, so that calcium could not pass through. "If a drug could be
designed to block this ion channel specifically, it could be taken by men or women.It would
not have to be taken for a very long period to block fertilisation, perhaps only just before or
after intercourse", said Dr Chapman.