Dads deliver more than DNA

Sperm contribute paternal DNA when they fertilise an egg - but they also deliver some mRNA messenger RNA, US researchers say. The unexpected finding means that sperm could play a greater role in early development than previously thought, say the scientists, who reported their results in the journal Nature. The research could have implications for research into infertility and its treatment. It could also help explain why cloning techniques have such a low success rate, since they involve the transfer of DNA only.

Messenger RNA is an intermediate stage between a gene and the protein for which it codes. The cell uses an mRNA template when making a protein, rather than reading the DNA code directly. Sperm contribute a set of paternal genes, made of DNA, to the fertilised egg, but until now it was thought that none of these had yet been copied into mRNA. However, scientists at the Wayne State University in Detroit have identified six mRNA molecules that are present in sperm and fertilised eggs, but not in unfertilised eggs. This, they say, implies that they are delivered to the egg by the sperm.

The researchers think that the sperm mRNAs could be important 'switches', which trigger embryo development and help the fertilised egg to implant in the womb. One of the RNA molecules makes a protein called clusterin, which is known to be important in fertilisation and embryo development. Team leader Stephen Krawetz hopes that the discovery will shed light on infertility: if sperm are missing one of these crucial mRNA molecules, they may be unable to fertilise an egg effectively.

The same mRNA molecules may be the reason why cloning is so technically difficult: 'Cloning requires an egg to develop without sperm fertilisation, and although an egg may be manipulated or "tricked" in the laboratory some of the time, embryonic growth generally requires an activation signal that comes from the male sperm', Krawetz said, adding 'Dad indeed has a function'.