How sperm and egg fuse into one - Fusion protein could be targeted to stop parasites from...

Nature News ^ | 25 March 2008 | Claire Ainsworth

[neverdem]

Fusion protein could be targeted to stop parasites from reproducing.

When two become one: the mysterious process of fertilisation.
Getty

Boy meets girl. Sperm meets egg. Now, scientists are a step closer to understanding the climax of this eternal love story: how sperm and egg merge to create a brand new individual.

“It’s really the defining moment in an organism,” says William Snell, a biologist at the University of Texas Southwestern Medical Center in Dallas, Texas, who headed one of the teams that made the find.

Snell, along with a group in Britain, discovered that a protein called HAP2 is involved with the fusion of egg and sperm, and found it in a wide range of species.

As well as shedding new light on fertilization, the discovery opens up a possible new avenue to tackling parasite-carried diseases such as malaria: targeting HAP2 with drugs or vaccines could perhaps stop a parasite’s sex cells from consummating their union, preventing them from replicating.

Come together

Broadly speaking, fertilization happens in two main phases: in the first, a sperm recognizes an egg, sticks to its jelly-like coating and strips to reveal parts of its cell membrane. In the second phase, the cell membranes of the egg and sperm cling together in an intimate embrace, before fusing to allow the DNA to meet.

Despite its importance, scientists know relatively little about the molecules that control fertilization. One issue is that many of the proteins that allow sperm and egg to recognize and stick to each other are unique to each species. This stops one species from accidentally fertilizing another, and the rapid evolution of some of these recognition proteins is thought to play a role in the formation of new species.

Snell and his colleagues looked at the details of the sex life of a slimy green single-cell alga called Chlamydomonas reinhardtii , which is easy to manipulate genetically. They found one mutation in a gene called HAP2 that prevented membrane fusion, but which left the earlier stages of recognition and attachment unaffected.

HAP2 was already known to be involved in plant fertilisation. Surprisingly, when the researchers scanned gene databases for HAP2, they found it in a wide range of organisms: from single-celled parasites such as malaria, to insects, simple animals such as sea anemones, and choanoflagellates — single-celled creatures that are the closest living relatives of multicellular animals. “The very first animal would have had this gene,” says Oliver Billker, who led the UK team from his lab at Imperial College, London. So far, however, the researchers have been unable to find the gene in mammals, including humans.

Making it work

Billker, a malaria expert now at the Wellcome Trust Sanger Institute near Cambridge, UK, studied the behaviour of HAP2 in the rodent malaria parasite, Plasmodium berghei . Parasite sex cells lacking HAP2 were unable to fuse, and so were unable to reproduce inside a mosquito.

This might make HAP2 a possible target for an anti-malaria vaccine, although both Snell and Billker emphasize that it is too early to tell if this would work. Other parasites, including those that cause toxoplasmosis and sleeping sickness, also have HAP2 genes.

So why is HAP2 so common between different species, while the proteins involved in sperm-egg recognition are not? One possible answer, says Snell, is that it helps organisms resolve two conflicting evolutionary demands: the need to maintain working machinery for membrane fusion, and the need to evolve species-specific sperm–egg interactions.

Janice Evans, an expert on fertilization biology at Johns Hopkins Bloomberg School of Public Health in Baltimore, Maryland, says the presence of HAP2 in so many different organisms is striking. “The fact that this gene has been around in life on Earth for so long makes you think it might be doing something important,” she says. As well as offering insights into the reproductive physiology of different species, HAP2 opens a new window on membrane biology. “This sets the stage for thinking about another mechanism for how membranes can fuse,” she says.

References Liu Y. et al. Genes & Development 22, 1051-1668 (2008)

[A CA Guy]

Wonder if some day they will cure the ones that would normally grow up to become parasites?

[rabscuttle385]

Wonder if some day they will cure the ones that would normally grow up to become parasites?

Hey, be nice to the Democrats.

[dr_lew]

“It’s really the defining moment in an organism,” says William Snell, a biologist at the University of Texas Southwestern Medical Center in Dallas, Texas, who headed one of the teams that made the find.

Are you prepared to sign an affidavit to that effect, Dr. Snell ?

[Yossarian]

“It’s really the defining moment in an organism,” says William Snell, a biologist at the University of Texas Southwestern Medical Center in Dallas, Texas,

Yeah, this is common sense. Hey, Doc - can you go and try to explain this simple insight to the pro-death abortion community, please?

(...) the discovery opens up a possible new avenue to tackling parasite-carried diseases such as malaria: targeting HAP2 with drugs or vaccines could perhaps stop a parasite’s sex cells from consummating their union, preventing them from replicating.

Ah, let's be a bit careful with such drugs or vaccines...

Any monkeying with such a critical life process as reproduction can have, well, how to say, a "wide ranging impact".

To put it lightly.

[fieldmarshaldj]

[Bushwacker777]

The creation of life is so complicated and miraculous — that fact is recognized by conservatives in general while liberals just see a lump of tissue.

Conservative view of fertilization: The start of a new baby.

Liberal view: A parasite has begun.