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The lifeline between a mother and her unborn baby
The Evolutionary Story of the Placenta
By Joshua Hill Tuesday, April 15, 2008Whenever you hear of the placenta, it’s usually because some hippie mum decided to serve it as pâté at a party she hosted to honor the birth of her baby. More often than not, people hear the word placenta and immediately tune out. To those of you still reading, this is not about eating placentas.
The placenta has long been the focus of much scientific endeavor, in an attempt to nail down just what it does, how it works, and why it came about.
New research from the Stanford University School of Medicine has uncovered the first clues for the placenta’s origins. The lifeline between a mother and her unborn baby, nourishing, providing oxygen, and protecting from danger; the placenta is critical to the baby’s health.
“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, PhD, assistant professor of genetics at Stanford USM, and senior author of the study to be published in the May issue of Genome Research.
The evidence gathered by Baker and her research team suggests that the modern day placenta, evident in all mammals, evolved from a much simpler tissue that was attached to the inside of eggshells. This tissue allowed our distant ancestors, the birds and reptiles that we emerged from (ignoring religious debate), to get oxygen.
Dr. Baker and her graduate student, Kirstin Knox, who was the study’s first author, addressed the placenta’s evolutionary status by determining which genes are active in cells of the placenta during pregnancy in mice. Two stages were found to exist throughout the pregnancy.
Stage one ran from conception through to mid-gestation, and involved the placental cells activating genes that mammals have in common with birds and reptiles. This evidence suggests that the placenta evolved through a repurposing of genes that early mammals inherited from their immediate ancestors.
Stage two saw the placenta switch to a new wave of species-specific genes, in which mice activated newly evolved mice genes and humans activated human genes, and so on. 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
Baker noted that these findings are especially interesting given that cloned mice are at a high risk of dying as the placenta’s genetic transition takes place. “There’s obviously a huge regulatory change that takes place,” she said. But while there is a massive shift taking place in the placenta genetically, the tissue doesn’t change in appearance.
All of this research is not just a study for no reason; understanding the origins from which the placenta evolved and how it functions could prove useful in other studies. Previously, studies have suggested that the placenta may contribute to triggering the onset of maternal labor, and is also suspected to be involved in pre-eclampsia, which is a leading cause of premature births.
HYPERLINK “http://www.earthtimes.org/articles/show/clues-to-ancestral-origin-of-placenta-emerge-in-stanford-study,350991.shtml” http://www.earthtimes.org/articles/show/clues-to-ancestral-origin-of-placenta-emerge-in-stanford-study,350991.shtml
