Genes-R-Us — Carrying our children’s DNA beyond the womb
Posted: Wednesday, October 3, 2012 8:00 pm
One of great things about science is that the “facts” keep evolving, especially with many the technological breakthroughs afforded by genomic sequencing.
The placenta, which was once thought to keep fetal blood and cells from the mixing with the mother’s blood, turns out to be a bit “leaky.” Thus, fetal DNA can show up in mom’s blood. This foreign DNA was thought to clear from mom’s body eventually. That was before last week.
Conversely, the permeability of the womb means that her children can also carry a small number of their mother’s cells into adulthood.
The function of the blood-brain barrier (BBB) is to keep blood separate from the brain’s extracellular fluid. The BBB protects our brain from large hostile molecules, like bacteria, while glucose and small molecules like oxygen, carbon dioxide, hormones and certain medications are allowed to pass through.
Last week the world learned that the BBB can permit fetal DNA to pass through, in some cases, giving rise to a permanent deposit fetal DNA in the female brain (http://bit.ly/PpmnIA).
Mom can retain bits of fetal DNA from all her children.
Fetal DNA had previously been identified in cells found within Mom’s blood, lymphatic tissue, liver, heart and lungs.
But never before had fetal DNA been found in the brain. The Fred Hutchinson Research Center in Seattle performed the new research.
Microchimerism is the scientific term used when one individual carries even a few cells from a genetic distinct individual.
What was the motivation for this research? Women are more likely to develop Alzheimer’s disease (AD) than men. Several studies had pointed to an additional risk for each additional child a woman had carried — which lowers her lifetime exposure to estrogen.
Declining estrogen levels were and are thought to be part of female AD problem. Before hormone replacement therapy received a “bad rap” from the Women’s Health Initiative, estrogen was commonly prescribed to help with female cognitive problems associated with aging. Unlike men whose estrogen levels do not decline with age, women’s estrogen levels decline dramatically with menopause.
How was this discovery made? The brains of 59 women were donated to science. Unfortunately, AD is only formally diagnosed through post-mortem brain study. Of those 59 women, 33 had AD and 26 were free from any neurological issues. Scientists looked for a specific male-only marker, DYS14 in all the women’s brains.
DYS14 is found within the gene that codes for the TSPY1 protein, which is responsible for testis development in males. This marker was found throughout the brains of the majority of the women in the study, presumably from carrying male children.
This is not to say that the female fetus fails to deposit DNA — it was simply easier to test for a male only gene as the woman could not have supplied that gene on her own.
“Male microchimerism was detected in 63 percent of subjects, was distributed in multiple brain regions and was potentially persistent throughout the human lifespan.” (http://bit.ly/PpmnIA) The oldest woman carrying male DNA in her brain cells was 94 years old.
Some women were known to have had male children yet no foreign DNA was found in their brains.
Other women were thought to have given birth to no male children, yet harbored the male DNA snippets.
A miscarriage, even if the woman was not aware of the pregnancy, or an elective abortion, apparently still supply enough fetal DNA that male microchimerism is possible in female brains.
It is unknown why microchimerism occurs in the brains of some women but not in others.
Although the number of women was small (59 in total), the women with AD has less foreign DNA (29 percent) in their brains than the women with the healthy brains (69 percent). This was an unexpected result. It would seem that retained fetal cells have the potential to be beneficial — much as they appear to be in some forms of breast cancer.
Was the male DNA integrated into functioning brain cells for these women? In separate research by the Fred Hutchinson Research Center, on one woman’s brain, the microchimeric brain cells were integrated into functioning neural (brain) cells. This result had already been established earlier studies in mice.
It is not amazing that the tiniest human life, whether he/she survives to birth — by chance or choice — has the potential write a DNA-based inscription even within the mother’s brain?
Editor’s note: Nancy@Nancy MillerLatimer.com has worked in scientific research and development for 27 years. She blogs at NeuronalBeauty.BlogSpot.com
Published in The Messenger 10.3.12