Posted on behalf of Lee Sweetlove.
A rabbit-sized species of kangaroo has become the third marsupial to have its genome sequenced, after the grey short-tailed opossum and Tasmanian devil. The sequence of the tammar wallaby, reported in Genome Biology, provides new insights into marsupial biology, such as how barely developed newborns the size of a kidney bean are able to find and crawl into the mother’s pouch.
The sequencing project was led by Marilyn Renfree, director of the Centre of Excellence for Kangaroo Genomics (KanGO), based in Canberra. The work follows up Australia’s first foray into genome science in 2008 when the KanGO team produced a physical map of the tammar genome.
Marsupial sequences act as a reference point for a key stage in mammalian evolution – the divergence of marsupials and placental animals (including humans) 180 million years ago. “The tammar wallaby sequencing project has provided us with many possibilities for understanding how marsupials are so different to us,” said Renfree in a press release.
The tammar genome sequence reveals that several gene families relating to unique aspects of marsupial biology are substantially larger than their couterparts in placental mammals. For example, the tammar genome contains one of the largest families of mammalian olfactory receptor genes with 1,500 members. This means the tammar can detect a remarkably wide range of odours, which might help the newborn wallaby to sniff its way towards its mother’s pouch.
The work also reveals gene expression patterns that may explain the kangaroo’s unusual asymmetric limb development. At birth, the forelimbs are highly developed, to allow the newborn to climb into the mothers pouch whereas the hindlimb, which eventually becomes dominant, is barely formed. The authors identify marsupial-specific patterns of expression of HOX genes that could be the key to the Kangaroo’s hop.
Image courtesy of Geoffrey Shaw.
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