Humble opossum's genetic map sheds light on humans

WASHINGTON (Reuters) - Scientists have mapped the genetic composition of a marsupial mammal, the South American gray, short-tailed opossum, gaining insight into the role of "junk DNA" in human evolution and into immune systems.

Because this opossum develops melanoma skin cancer much as people do and its newborns can regenerate a severed spinal cord, scientists hope studying its genome can boost research into treating human skin cancer and neurological ailments.

In research published on Wednesday, the furry creature -- twice as big as a mouse and with a prehensile tail -- became the first marsupial to have its DNA decoded.

Using the opossum as a comparison helped identify genetic elements present in placental mammals but absent in marsupials, helping to fill a hole in the understanding of how mammalian genomes have evolved over tens of millions of years and giving a new look at the evolutionary origins of the human genome.

A fifth of the human genome's key functional elements arose after the divergence from marsupials, the research found. Most of these innovations occurred not in protein-coding genes but in areas of the genome that do not contain genes and until recently had been derided as junk DNA, they found.
Marsupials give live birth, without the long gestation of placental mammals, to tiny babies at a very early stage of development that climb from the birth canal to the mother's nipples, where they latch on for weeks or months. Examples include the kangaroo, wallaby and koala.

The most primitive mammals are monotremes, which lay eggs rather than having live birth. They include only the duck-billed platypus and echidna, also known as the spiny anteater. Scientists are working on the first monotreme genome, for the platypus.

Katherine Belov of the University of Sydney in Australia said the research showed the complex mammalian immune system -- the body's natural defenses -- arose before the two lineages separated.

Source :   http://www.reuters.com