Platypus genome mapping boon for human and livestock researchers

Thursday 8 May 2008, 2:19PM

By University of Otago


Evolution Platypus
Evolution Platypus Credit:


In decoding the genome of the platypus, a team of researchers from the United States, Australia, England, Germany, Israel, Japan, Spain and New Zealand has revealed important information that will enhance our understanding of other mammals and may lead to the development of new approaches to combat disease in livestock and humans and enhance livestock productivity.

The New Zealand researchers have been collaborating with the international consortium of scientists, led by the Washington University School of Medicine in St Louis. Its findings are this week's cover story for respected international science journal 'Nature'.

The Nature paper analyzes the genome sequence of a female platypus named Glennie from New South Wales, Australia. The project was largely funded by the National Human Genome Research Institute, part of the US Government's medical research agency, the National Institutes of Health.

Professor Neil Gemmell, who was recently appointed to the AgResearch Chair in Reproduction and Genomics at the University of Otago, led the New Zealand based researchers working on the project whilst at the University of Canterbury.

As holder of the AgResearch Chair, Professor Gemmell is the first Director of the recently established Centre for Reproduction and Genomics, which brings together the expertise of AgResearch and University scientists.

Professor Gemmell says the platypus is an important animal to study because it is only one of three living monotreme mammals that likely best represent what ancient mammalian ancestors were like when they evolved over 166 million years ago. Understanding the genetic make-up of the platypus tells us what genetic features are common to all mammals, and what features are unique to other mammals including livestock and humans; information that may tell us much about how mammals evolved.

"You could say that some of the central genetic building blocks on which all mammals are constructed are contained within the genome of this remarkable animal, and become apparent to us when we compare the platypus to the other mammalian genomes (human, mouse, dog, possum) already sequenced.

"It is representative of an ancient mammalian group that shares some of the features common to reptiles and birds such as egg laying but exhibits behaviours and traits, like producing milk and suckling its young; traits that define the mammals.

Professor Gemmell and his team used supercomputer resources at the University of Canterbury to analyse the genomic distribution and abundance of small repetitive DNA sequences (microsatellites) in the platypus genome that are predominantly viewed as having few, if any, functions. However, Gemmell's team demonstrated that a substantial proportion of these repetitive sequences were conserved in other species, with some conserved in humans, mice, dogs, possums and chickens.

"Scientists now believe that the reason this genetic material is passed down is because it is important in some way. It has been conserved across vast evolutionary time frames and is likely present in every single mammal that exists today."

He says the challenge for scientists now is to find out why this material has been passed down through countless generations and establish what functions it is responsible for.

The international project team compared the platypus genome with genomes of the human, mouse, dog, possum and chicken and found that the platypus shares 82 percent of its genes with them.

"By comparing the genome of this unusual mammal to others that have already been sequenced we hope to be able to gain new insights into mammalian reproduction. The platypus has many more sex chromosomes – the organised structures into which DNA is packed that determine sex – than do humans. The platypus has ten sex chromosomes, compared with our two. Furthermore, the chromosomes responsible for determining sex are more similar to those in birds than in mammals. Despite the obvious differences, there are likely common elements responsible for determining sex in both systems.

"We believe this work will lead to major insights into mammalian sex determination, reproduction and development potentially leading to innovative new treatments and therapies for humans and livestock that will benefit human health and help farmers raise productivity."

Professor Gemmell says that while it may seem an obscure animal to study, its unique make-up could lead to significant advancements in scientific knowledge.

"For example, the male platypus produces venom, which it delivers from spurs on its legs. The venom is a cocktail of proteins that originally had very different functions and incredibly the same proteins are found in snake venom even though platypus and snake venom evolved independently. Understanding more about platypus venom could lead to exciting new pharmaceutical developments."

The Centre for Reproduction and Genomics is expected to be an international leader in reproduction and genomics research. It will have a particular focus on livestock and human reproduction; livestock and human health and disease; and the control of mammalian reproduction.