Platypus genome reveals a treasure trove of evolutionary clues

Sequencing of the platypus genome is providing a ‘missing link’ for scientists as it yields important clues about how mammalian genes function and evolve.

Found only in Australia, the platypus (Ornithorhynchus anatinus) is a composite of reptilian, mammalian and its own unique characteristics. It has a duck bill, webbed feet, lays eggs and uses electro-reception in its bill to locate aquatic prey. Females lack nipples but suckle their young directly through pores in their abdominal skin, while males are equipped with venom similar to that of reptiles.

An international collaboration of researchers reports in Nature this week that it has been able to sequence and analyze the platypus genome, and has compared it with the genomic sequence of other mammals and the chicken.

The genomic sequence has helped to reveal: the origins of genomic imprinting in vertebrates; that platypus venom proteins were co-opted independently from the same gene families that provided reptile venom; that milk protein genes are conserved; and that immune gene family expansions are directly related to platypus biology. According to the authors, some of these expansions may arm the immunologically naïve young with a diverse arsenal of innate immune responses.

Originally considered a true mammal despite its rich list of unique characteristics, the platypus is classified as a monotreme along with the echidna. Monotremes are a subclass of egg-laying mammals estimated to have diverged from other mammals around 166 million years ago.

A better understanding of platypus genetics will also be important for monotreme conservation. The platypus was recently classified as ‘vulnerable’ because of its reliance on aquatic environments under stress from human activities and climate change.

Led by Wesley Warren from the Washington University School of Medicine in Missouri USA, the research team included over 100 scientists from the United States, Australia, the United Kingdom, Spain, Israel, New Zealand, Germany, France and Japan.