The first analysis of the genome sequence of the duck-billed platypus was published today by an international team of scientists, revealing clues about how genomes were organized during the early evolution of mammals. The research was supported in part by the National Human Genome Research Institute (NHGRI), part of the National Institutes of Health (NIH).
Fans of TV nature shows will remember that the duck-billed platypus, native to Australia, is one of the few mammals that lay eggs. However, platypus peculiarity does not end there. For example, these odd animals boast what looks like a duck’s bill, which houses an electrosensory system used when foraging for food underwater, and a thick fur coat to adapt to the icy waters in which it resides. Males also possess hind leg spurs that can deliver venom powerful enough to wound territorial competitors during mating season, or cause excruciating pain in other mammals, including humans.
“At first glance, the platypus appears as if it was the result of an evolutionary accident. But as weird as this animal looks, its genome sequence is priceless for understanding how fundamental mammalian biological processes have evolved,” said Francis S. Collins, M.D., Ph.D., director of NHGRI. “Comparisons of the platypus genome to those of other mammals will provide new insights into the history, structure and function of our own genome.”
In a paper published in today’s issue of the journal Nature, researchers analyzed a high-quality draft genome sequence of Glennie, a female platypus from Australia. The consortium included scientists from the United States, Australia, England, Germany, Israel, Japan, New Zealand and Spain. Sequencing of the platypus genome was led by the Genome Sequencing Center at Washington University School of Medicine in St. Louis, a part of NHGRI’s Large-Scale Sequencing Research Network.
Once the sequence was produced, researchers began comparing the genome of the platypus, whose ancestors split from the rest of mammalian lineage some 166 million years ago, with the well-characterized genomes of the human, mouse, dog, opossum and chicken, as well as the draft genome sequence of the green anole lizard. The chicken genome was chosen because it is descended from the ancestral group of egg-laying animals, including extinct reptiles, who passed on much of their DNA to animals like the platypus. Scientists were particularly interested in finding features within the platypus genome that could explain the odd mix of characteristics seen in the platypus: those that were more like reptiles, birds and mammals.
The team found that the platypus genome contains about the same number of protein-coding genes as other mammals — approximately 18,500. The platypus also shares more than 80 percent of its genes with other mammals whose genomes have been sequenced. Next, researchers combed the platypus genome looking for genetic evidence of sequences unique to platypuses that have been lost from mammalian genomes. Scientists were also eager to find out what characteristics of the platypus were linked at the DNA level to reptiles or mammals.
“The mix of reptilian, mammalian and unique characteristics of the platypus genome provides many clues to the function and evolution of all mammalian genomes,” said Richard K. Wilson, Ph.D., director of Washington University School of Medicine’s Genome Sequencing Center and the paper’s senior author. “Now, we’ll be able to pinpoint genes that have been conserved throughout evolution, as well as those that have been lost or gained.”