Our placenta came from eggs of birds and reptiles

April 19th, 2008 - 5:30 pm ICT by admin  

Washington, April 19 (IANS) Researchers have unearthed clues about the ancient origins of placenta, a mother’s intricate lifeline to her unborn baby supplying oxygen and vital nutrients. The evidence suggests the placenta of humans and other mammals evolved from the much simpler tissue that attached itself to the inside of eggshells and enabled the embryos of our distant ancestors, the birds and reptiles, to get oxygen.

“The placenta is this amazing, complex structure and it’s unique to mammals, but we’ve had no idea what its evolutionary origins are,” said Julie Baker of Stanford University.

The placenta grows inside the mother’s uterus and serves as a way of exchanging gas and nutrients between mother and foetus; it is expelled from the mother’s body after the birth of a baby.

It is the only organ to develop in adulthood and is the only one with a defined end date, Baker said, making the placenta of interest to people curious about how tissues and organs develop, reports Sciencedaily.

“The placenta seems to be critical for foetal health and maternal heath,” Baker said. Despite its major impact, almost nothing was known about how the placenta evolved or how it functions.

Baker and Kirstin Knox of Stanford, the study’s co-authors, began addressing the question of the placenta’s evolution by determining which genes are active in cells of the placenta throughout pregnancy in mice.

They found that the placenta develops in two distinct stages. In the first stage, which runs from the beginning of pregnancy through mid-gestation, the placental cells primarily activate genes that mammals have in common with birds and reptiles.

In the second stage, cells of the mammalian placenta switch to a new wave of species-specific genes. Mice activate newly evolved mouse genes and humans activate human genes.

An elephant’s placenta nourishes a single animal for 660 days. A pregnant mouse gestates an average of 12 offspring for 20 days. Clearly, those two pregnancies would require very different placentas, said Baker.

These findings will be published in the May issue of Genome Research.

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