Platypus study reveals 160 million years of separation

Genetics

A four-year international research project to sequence the entire genetic record of the platypus over the past 160 million years has revealed new insights into the biology of Australia's famous icon.

University of Adelaide geneticists Dr Frank Grützner and Dr Enkhjargal Tsend-Ayush, together with more than 100 researchers worldwide, have collaborated on the platypus genome project, published as the cover story last month in the world's most prestigious scientific journal, Nature.

The leading authors of the paper, including Dr Grützner, revealed the key discoveries that researchers have made in the course of the project.

"The platypus is an Australian treasure for science because it is unique for a number of reasons," Dr Grützner said. "They are our most distant mammalian relative, yet they are so different to us.

"They lay eggs and they suckle their young after they hatch, although they don't have nipples, so the milk is secreted from the abdominal surface.

"They have specialised neurons that help them catch their prey in the mud, they are venomous, they regulate their body temperature at 32 degrees (not 37 as most other mammals), their reproductive system is a mixture of reptilian and mammalian and they have 10 sex chromosomes.

"Now with the entire genome sequenced we can investigate their extraordinary features at the molecular level."

Dr Grützner made international headlines in 2004 when he discovered that the sex chromosomes of the platypus - our most distant mammalian relatives - were much closer to birds than humans.

"We now know that platypus sex chromosomes have no relation at all to mammals," Dr Grützner said.

One has to go back more than 160 million years to find the last common ancestor between humans and the platypus, the earliest living branch of the mammalian lineage.

Dr Grützner said evolution filters out important genes and the platypus genome sequencing project will help scientists look for vital clues in the development of all mammals.

Dr Grützner and his group within the School of Molecular and Biomedical Sciences at the University of Adelaide have been one of the key collaborators of the project, which has provided the first completed genome sequence of any mammal in Australia.

"Our work on this project is a long-term investment that helps our own research on the platypus. We can now identify platypus genes within minutes of searching a database whereas previously it could take up to a year, or longer.

"The platypus genome provides an enormous resource for every scientist interested in the biology of monotremes and in the evolution of mammals, including humans."

The project, which started in 2004, was led by the Washington University Sequencing Centre, with funding from the National Institutes of Health in the United States as well as the Australian Research Council.

Dr Grützner joined the School of Molecular and Biomedical Sciences at the University of Adelaide in 2005 as a lecturer and took up an ARC Australian Research Fellowship in 2006.

Originally from Germany, he completed his PhD at the Max Planck Institute for Molecular Genetics in Berlin. In 2001 he secured an ARC Postdoctoral Fellowship with Professor Jenny Graves at the Australian National University, studying reptiles, marsupials and monotremes. Professor Graves is also one of the leading authors of this Nature paper.

Dr Grützner was among eight South Australians to be named a Young Tall Poppy of Science for 2007/08 in recognition of his outstanding work.

Story by Candy Gibson