Cells from your mother may have penetrated your brain when you were a fetus. These alien, or 鈥渕icrochimeric鈥�, cells then seem to take up residence and perform a range of jobs, even into old age.
The discovery shows that 鈥渆very human brain is likely a genetic mosaic of more than one person鈥�, says at the Icahn School of Medicine at Mount Sinai in New York, who wasn鈥檛 involved in the research.
We already knew that we have cells from our mothers 鈥� and other family members 鈥� inside us. This is thought to be because of a small proportion of cells crossing the placenta while we鈥檙e in utero, which could influence our risk of autoimmune conditions, while also playing a role in tissue repair.
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There is evidence that these cells , where they can . But the extent of this, and the role the cells play there, was less clear. This is because brain samples from both a mother and their child are needed for comparison, and even if you have these samples, the cells can be hard to spot, says at the Fred Hutchinson Cancer Center in Seattle. 鈥淭hey are usually 1 in 100,000.鈥�
Now, Kanaan and his colleagues have analysed genetic sequences in samples removed from the brains of 37 children 鈥� from newborns to 14-year-olds 鈥� as part of surgery to treat epilepsy. These were compared against genetic sequences in mouth swabs taken from their mothers.
The researchers used a technique called single-nucleus RNA sequencing to identify genetic arrangements in the samples that were from just the child or their mother. They then ran a tool they had previously developed, called , to computationally look for patterns in the sequence data. 鈥淚t was just magical. It models data, and it says 鈥榯hat cell does not fit in that model, so it鈥檚 probably a foreign cell鈥�,鈥� says Kanaan.
The team found maternal cells in 26 of the 37 children, with each sample having 2.2 maternal cells per 100,000, on average. More of these children probably had maternal cells, says Kanaan, but the method would have missed instances in which the mother and child had identical genetic variants.
鈥淚鈥檓 very excited about this,鈥� says Chaudhry, 鈥渂ecause they鈥檝e used some very sophisticated methods to really answer the question of 鈥榠s there microchimerism?鈥欌��
Kanaan and his colleagues identified microchimeric cells working in many cell types, including neurons (nerve cells that transmit information), microglia (the brain鈥檚 immune cells), astrocytes (which support neurons), oligodendrocytes (which create the protective sheath around neurons) and endothelial cells (which line blood vessels).
In another part of the experiment, the team used Cellector to analyse RNA sequence data from three previously published studies. These comprised individuals ranging in age from a 22-week-old fetus to people in their 80s.
This revealed that people of all ages can have microchimeric cells in their brains. However, the number declined with age. This decline may be the result of apoptosis, programmed cell death that removes damaged and old cells.
鈥淚t is crazy that we found them in gestational samples,鈥� says Kanaan. 鈥淚t鈥檚 a [widespread] human feature to have this, and it starts in early life and continues throughout the whole life, which is mind-blowing.鈥�
bioRxiv
