Sperm unexpectedly inject RNA into the eggs they fertilise, possibly kickstarting crucial development of the embryo, suggests a study of human sperm.
The discovery overthrows conventional assumptions that sperm simply deliver DNA, leaving the egg itself to steer early development after fertilisation.
鈥淭he most important thing is that dad鈥檚 doing a little more than just adding his DNA,鈥� says Stephen Krawetz, head of the team at Wayne State University in Detroit, Michigan, US that made the discovery.
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The findings provide new clues to the origins of infertility, and new leads for treatments.
And it provides a tantalising explanation for the low efficiency of cloning. Creating a cloned embryo by combining an existing cell with an empty egg requires no sperm, and so lacks RNA which might hold the key to embryonic development.
Hamster eggs
In earlier research, Krawetz and his colleagues discovered 3000 RNA molecules packaged away in sperm.
Working with David Miller and his colleagues at the University of Leeds in the UK, Krawetz鈥檚 team has now identified six RNA molecules present in human sperm but not unfertilised eggs.
鈥淲e think it opens up the possibility that there are some early developmental switches set off by these RNAs which enable implanation of the oocyte and early embryonic development,鈥� he told 快猫短视频.
In further experiments using human sperm to 鈥渇ertilise鈥� hamster eggs, they proved that two of the RNA molecules 鈥� which carry instructions for the proteins protamine-2 and clusterin 鈥� ended up in the hamster eggs.
鈥淐lusterin鈥檚 involved in numerous processes in fertilisation and healthy embryonic development,鈥� says Krawetz.
RNA 鈥榝ingerprint鈥�
Since then, his team has discovered other potentially active RNA molecules in sperm, and is hopeful that they will throw new light on infertility, perhaps revealing what happens when certain RNA molecules are faulty or not made at all.
鈥淲e鈥檝e developed a male fertility RNA 鈥榝ingerprint鈥�,鈥� he says. The hope is that through comparisons with 鈥渇ingerprints鈥� of infertile males, it may be possible to spot sperm RNA which has a critical role in embryonic implantation, reprogramming and development.
As well as explaining why some couples may not be able to conceive, the discovery means it may one day be possible to provide missing RNA molecules through in-vitro fertilisation. The same ploy might also be used to improve the efficiency of cloning.
Journal reference: Nature (vol 429, p 153)