Baby’s Cells Can Handle Mom’s Body for Decades | Science
Mothers around the world say they feel like their children are still a part of them long after childbirth. It turns out to be literally true. During pregnancy, the cells of the fetus cross the placenta and enter the mother’s body, where they can become part of her tissues.
This cell invasion means that mothers carry unique genetic material from their children’s bodies, creating what biologists call a microchimer, named after the legendary beasts made of different animals. The phenomenon is widespread in mammals, and scientists have proposed a number of theories on how it affects the mother, from better wound healing to a higher risk of cancer.
Now, a team of biologists argues that in order to truly understand what microchimerism does to moms, we need to understand why it evolved in the first place.
“What we hope to do is not only provide an evolutionary framework for understanding how and why microchimerism arose, but also to assess how it affects health,” says the lead author. Amy boddy, geneticist at Arizona State University.
Maternal-fetal conflict has its origins in the first placental mammals millions of years ago. During evolution, the fetus evolved to manipulate the physiology of the mother and increase the transfer of resources such as nutrition and warmth to the developing child. The mother’s body in turn has developed countermeasures to prevent an excessive flow of resources.
Things get even more intriguing when the fetal cells cross the placenta and enter the mother’s bloodstream. Like stem cells, fetal cells are pluripotent, which means they can develop in many types of tissues. Once in the mother’s blood, these cells travel around the body and lodge in the tissues. They then use chemical signals from neighboring cells to develop into the same substance as the surrounding tissue, Boddy explains.
Although the mother’s immune system usually removes unchanged fetal cells from the blood after pregnancy, those that have already integrated into maternal tissues escape detection and may remain in the mother’s body.
Microchimerism can become particularly complex when a mother has multiple pregnancies. The mother’s body accumulates cells from each baby and potentially functions as a reservoir, transferring cells from the older brother to the younger one and forming more elaborate microchimers. The presence of fetal cells in the mother’s body might even regulate how quickly she can get pregnant again.
“I think a promising area for further research concerns unexplained pregnancy loss, and whether older siblings, as genetic individuals, may play a role in delaying the birth of older siblings. young “, says David Haig, evolutionary biologist at Harvard University.
Given all of this complexity, microchimers have been difficult to study until recently, the authors note in their paper, which will be published in a next issue of Bioassays. The phenomenon was discovered decades ago when male DNA was detected in the blood of a woman. But the technologies of the day couldn’t get a sufficiently detailed picture of genetics to unravel the tiny cellular situation.
Now, deep sequencing technologies allow researchers to identify the origin of DNA in a mother’s tissues more fully by sampling many areas of the genome, including genes involved in immunity. These genes are unique to an individual and can therefore help differentiate a mother’s DNA from that of her children with greater precision.
“If cell populations can be isolated, modern techniques should unambiguously identify the original genetic individual,” says Haig.
Still, understanding how fetal cells interact with maternal cells is going to be difficult, Boddy says. Little is understood about the cell signaling that causes fetal cells to regulate maternal physiology.
“It’s probably a negotiation between the maternal body and the fetal cells, where there is an expectation in the maternal body of a certain level of microchimerism that it needs to function properly,” Boddy said. For example, previous experiences showed that when mouse fetal cells are exposed to lactation hormones in the lab, they take on attributes similar to breast cells, suggesting that breast tissue may be a hotspot for microchimerism.
“Normal, healthy lactation may be the result of fetal cells signaling the mother’s body to produce milk,” says co-author Melissa Wilson Sayres, also in the state of Arizona. But previous work has also suggested that the same characteristics that allow fetal cells to integrate into mother’s tissues, such as evading her immune system, also make them similar to cancer cells, which could lead to greater vulnerability. to cancer in the mother.
Based on evolutionary reasoning, the authors predict that fetal cells should be found primarily in tissues that play a role in transferring resources to the fetus. This includes the breast, where they can impact milk production; the thyroid, where they can affect metabolism and heat transfer to the baby; and the brain, where they can influence neural circuitry and maternal attachment to the child.
The next steps will be to use modern sequencing tools to search for fetal cells in these locations, and then begin to study how cells communicate in each region of the mother’s body.
“What is really interesting and new about this work is to place the issue of microchimerism and maternal health in an evolutionary framework,” says Julienne Rutherford, biological anthropologist at the University of Illinois at Chicago.
“If these fetal cells interact with maternal physiology, where in the maternal body would we expect the greatest effect on function? This has been a big question mark. Putting this in an evolving context was incredibly smart and new and very exciting. It is a fine example of a theory leading to verifiable predictions. “
EDITOR’S NOTE: This story has been updated to clarify the results of the study on mouse fetal cells and breast tissue.