Sperm really can tell us everything we ever wanted to know about sex

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The Independent Online

Woody Allen's famous portrayal of a neurotic sperm in Everything You Always Wanted To Know About Sex was based on comic intuition rather than academic study. But now scientists claim to have uncovered for the first time the complex workings of the male sex cell.

According to a new study, far from being a relatively insignificant contribution to the sexual act - a simple vehicle for delivering a man's DNA to the egg of a woman - the sperm is the gastronomic equivalent of a six-course meal.

Scientists have identified the hundreds of proteins that constitute the head and tail of the smallest cell in a man's body - so small that about 500 million of them can fit into a teaspoon.

They believe the proteins could lead to new insights into how the sperm manages the equivalent of a transatlantic swim as well as sabotaging the efforts of rival sperm in the race to be first to reach the egg.

Teasing apart the protein building blocks of a sperm could also shed light on the causes of male infertility as well as the evolutionary origins of sex, said Tim Karr, a biologist at the University of Bath. "If we can work out what makes one sperm more successful than another, we might be able to apply this knowledge to clinical therapies for the treatment of sperm that are not functioning properly," Dr Karr said.

The study, published in the journal Nature Genetics, was carried out on the sperm of fruit fly but scientists believe that about half of the 381 proteins that they have now identified also exist in the human sperm cell.

The researchers plan to unlock the protein recipes of the sperm of different species, including humans.

"This is the first catalogue of sperm proteins for any organism, and it offers a tantalising glimpse into how we might begin to answer some of biology's most fundamental questions," Dr Karr said.

"Amazingly, we know very little about what is in a sperm, which probably explains why we don't really understand sex, let alone how it evolved," he said.

Until now, scientists have only known about a handful of proteins that are part of the assemblage of biological molecules that make up a sperm cell. Knowing the complete protein recipe - the proteome - extends our knowledge immensely, Dr Karr said.

"Being able to compare the structure and content of the proteome of sperm from different species should help us to understand the evolution and origin of sperm," he said.

Biologists believe that sperm has evolved an elaborate mechanism to interfere with the chances of a rival sperm being first to reach the egg.

"This question of sperm competition has baffled scientists for years," Dr Karr said.

Bath University's Steve Dorus, who took part in the study, said that knowing the proteins that make up a sperm cell will prove to be a vital tool for solving other mysteries. "The sperm proteome provides a basis for studying the critical functional components of sperm required for motility [swimming ability], fertilisation and possibly early embryo development. It should be a valuable tool in the study of infertility as more targeted studies can now be established in model organisms," he said.

"We can start to look for the 'core' sperm proteome, that is the most basic required constituents for sperm. This will not only shed light on the evolutionary origins of sperm, but may advance our understanding of the evolution of sex itself."

The story of sperm

* Sperm is produced in the testes where it takes around 10 weeks to reach maturity.

* Matured sperm is stored in the epididymis, which runs across the top of each testicle.

*The sperm is the smallest cell in the body and needs a balanced diet for energy.

* A healthy amount of sperm production requires a temperature three to five degrees below body temperature.

* An adult male can produce around 70 to 150 million a day.

* There are around three million at the tip of an erect penis.

* Sperm travels up to 28mph at the time of ejaculation.

* It travels from the epididymis through the vas deferens where it picks up a fluid rich in fructose, which acts like rocket fuel.

* It swims 12 inches per hour.

* Most of the ejaculate is made up of alkaline substances that aids the sperm on its journey.

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