The platypus genome could hold secrets to mammalian
evolution.
Image courtesy of Ian Elton, Healesville Sanctuary.

An international collaboration has led to the sequencing of the platypus genome, providing a missing link between mammalian and reptilian evolution.  

The paper, compiled by over 100 researchers, including 26 Australians, was published on 8 May 2008 on the front cover of Nature.

The platypus is the first Australian animal to have its genome sequenced and is well known for having characteristics of birds, mammals and reptiles.  

As well as revealing the significant findings of the genome, the Nature paper also discussed the implications of the results and opened up opportunities for future research in both monotremes and humans.

“It’s the comparisons of humans with the platypus that can tell us about the fork in the road, when the platypus went one way and we went another way,” said Professor Jenny Graves, a co-author of the paper, head of the Comparative Genomics Group at ANU and Director of the ARC Centre of Excellence for Kangaroo Genomics.

“The platypus genome will allow us to examine the evolution of mammalian specific characters such as warm bloodedness, lactation and genomic imprinting,” said Dr Andrew Pask a Research Fellow at the University of Melbourne’s Department of Zoology who was involved in the research.

Human health and medicine could also benefit from the study, according to Dr Sue Forrest, director of the Australian Genome Foundation.

She said that comparisons between the human and platypus genomes would enable better detection of the switches that turn genes on and off in our body, advance our knowledge of how our cells function and open up avenues for tackling disease in the human population.

The research could also provide clues as to how sex determination has evolved over the past 165 million years, said Dr Paul Waters, a co-author of the paper and Post Doctoral Fellow at the Australian National University and ARC Centre of Excellence for Kangaroo Genomics.

“To our surprise we discovered that the platypus X and Y chromosomes are completely unrelated to the X chromosome of all other mammals,” said Dr Waters.

“Platypus sex chromosomes share extensive similarity to the sex chromosomes of the distantly related birds, suggesting that our ancient mammal-like reptile ancestor might have had sex chromosomes more like those of the current day birds,” he said.

The research could also reveal how humans’ unique method of determining which genes are expressed in offspring, known as genomic imprinting, has developed, as it occurs in all mammals except monotremes, said Dr Pask and Professor Marilyn Renfree, a Federation Fellow at the University of Melbourne’s Department of Zoology.

“The platypus genome provides a unique resource in which to investigate the changes that have occurred to the genome with the acquisition of genomic imprinting”, said Dr Pask.

Another unique feature of the platypus that can be further explored through its genome is its venom, which is delivered on its spurs.

When humans are exposed to platypus venom they experience extreme swelling and terrible pain, which cannot be relieved by normal painkillers, said Camilla Whittington, co-author of the paper and a PhD student in the faculty of Veterinary Science at the University of Sydney.

Research into the venom could one day lead to the development of human medicines and pain killers, said Whittington.

However, as well as giving insights into human medicine and evolution, the paper has important implications for conservation of the platypus, which have suffered reduced number as a result of drought and habitat loss.

“We need to use this data to build strong links to the general biology of platypus and echidnas to help protect these fascinating and iconic creatures,” said Dr Frank Grützner, a co-author of the paper and Head of the Genome Organisation, Epigenetics and Sex Determination Laboratory Adelaide University.