Biological complexity:inflame then implant a placenta (Introduction)

by David Turell , Wednesday, January 10, 2018, 22:08 (2509 days ago) @ David Turell

Experimentation in animals has shown that molecules that cause inflammation help implant a placenta in mammals:

https://www.scientificamerican.com/article/armadillo-hedgehog-and-rabbit-genes-reveal-h...

a study of gene expression in early pregnancy, when the embryo implants in the uterus, suggests that placental mammals evolved the ability to turn an inflammatory attack on the embryo into an advantage.

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in placental mammals, the embryo does not simply cling to the uterus. Rather, it destroys the uterine lining as it invades the tissue, triggering a flood of inflammatory proteins. During infection and injury, these proteins normally fight invaders and repair wounds. Some of these proteins could be detrimental to a budding life form, but studies suggest that inflammation is necessary for an embryo. For instance, women who take anti-inflammatory drugs in the earliest days of pregnancy have a higher risk of miscarriage because the embryo does not successfully implant in the uterus. And reproductive biologists argue that certain aspects of inflammation, such as the growth of new blood vessels, help the developing embryo to get the oxygen and nutrients it needs.

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To find out how placental mammals are able to withstand the protein assault in these early days, Chavan analysed the inflammatory response in three of these species: the rabbit (Oryctolagus cuniculus), armadillo (Dasypus novemcinctus) and hedgehog (Echinops telfairi). An inflammatory protein, interleukin-17, that had been present in high levels in the opossum seemed to be inactive in the placental mammals—as if it had been switched off. The protein normally beckons white blood cells that kill invaders by digesting them or destroying them with enzymes. “It’s probably important to shut those down before they can damage the embryo,” Chavan says.

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His preliminary studies found that cells lining the uterus of placental mammals suppress the production of interleukin-17. Other aspects of the inflammatory response subside later in pregnancy, although it’s unclear what triggers this. The results suggest that placental mammals have fine-tuned inflammation over the course of pregnancy so that it waxes and wanes. “Mammals have figured out a way to keep some aspects of the inflammatory process that are favourable to the fetus, but stop the destructive parts of the response,” says Gunter Wagner, an evolutionary biologist at Yale and the senior investigator on the studies.

Comment: this finding presents the usual question of how it evolved. All of this process can damage the fetus, so the inflammatory event and its protective mechanism for the fetus must all develop simultaneously. Cannot be stepwise. Design in action.