Last man standing: just two Y-chromosome genes needed for reproduction

Male mice are able to reproduce healthy offspring with only two Y-chromosome genes, researchers at the University of Hawaii have discovered.

'Does this mean that the Y chromosome (or most of it) is no longer needed? Yes, given our current technological advances in assisted reproductive technologies', said Professor Monika Ward at the Institute for Biogenesis Research.

Ward and her colleagues produced transgenic mice that only had the Sry gene, critical in testes development, and the Eif2s3y gene, which is involved in the initial stages of sperm production, on their Y chromosomes.

These infertile mice then underwent an advanced form of IVF, called spermatid injection, where immature sperm cells are injected directly into the egg. They fathered pups that went on to have a normal lifespan and were capable of producing a second generation on their own without further assistance.

Professor Ward highlighted the importance of the Y chromosome for normal, unassisted fertilisation and other aspects of male reproduction. 'Most of the mouse Y-chromosome genes are necessary for normal fertilisation', she said. 'However, when it comes to assisted reproduction, our mouse study proves that the Y-chromosome contribution can be brought to a bare minimum'.

Speaking to BBC News, Dr Chris Tyler-Smith from the Wellcome Trust Sanger Institute, who was not involved in the research, said: 'This is a great step forward in understanding basic biology'.

Although their findings are not directly translatable to human male infertility cases, the research group argue that the advances in assisted reproduction methods could one day help infertile men with a damaged Y chromosome.

'It's quite an amazing technique to be able to get live, healthy offspring from round spermatid, which are way early in the final process of sperm maturation', said Polly Campbell, an evolutionary biologist at Oklahoma State University who was not involved in the research, speaking to The Scientist. 'That is probably the single most striking thing about this paper'.