Clues to ancestral origin of placenta emerge in Stanford study

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.

It makes sense that each animal would need a different set of genes, Baker said. "A pregnant orca has different needs than a mouse and so they had to come up with different hormonal solutions to solve their problems," she said. For example, 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.

Baker said these findings are particularly interesting given that cloned mice are at high risk of dying soon after the placenta's genetic transition takes place. "There's obviously a huge regulatory change that takes place," she said. What's surprising is that despite the dramatic shift taking place in the placenta, the tissue doesn't change in appearance.

Understanding the placenta's origins and function could prove useful. Previous studies suggest the placenta may contribute to triggering the onset of maternal labor, and is suspected to be involved in a maternal condition called pre-eclampsia, which is a leading cause of premature births.

Baker intends to follow up on this work by collaborating with Theo Palmer, PhD, associate professor of neurosurgery; Gill Bejerano, PhD, assistant professor of developmental biology, and Anna Penn, MD, PhD, assistant professor of pediatrics. Together, the group hopes to learn how the placenta protects the growing brain of the unborn baby, a protection that seems to extend into adulthood.

The work was funded by the National Institutes of Health, the March of Dimes and Stanford's Medical Scientist Training Program.

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