The placenta acts as a protective barrier for the baby during pregnancy and its normal structure is different from that of any other human organ. This is how forceful researchers from the Wellcome Sanger Institute and the University of Cambridge are, who claim that it resembles that of a tumor and that it harbors many of the same genetic mutations found in childhood cancers.
Their conclusions, published in the journal Nature, support the idea that the placenta is a repository of genetic defects and that the fetus corrects or avoids these errors.
How the placenta works
It is a fundamental organ in pregnancy, since it constitutes the vital connection of the baby with the mother. It begins to form at the same time the embryo is implanted in the uterine wall (approximately a week after fertilization has occurred) and develops from the same cells from the sperm and the egg that gave rise to the fetus.
Its main mission is to transmit nutrients to the baby and to act as a filter in charge of passing fetal waste into the maternal bloodstream to eliminate them, acting as a protective barrier.
But it is the first time that a high-resolution study has been carried out on the genomic architecture of the placenta to better understand its structure. The results provide a clear rationale for studying the association between genetic alterations in pregnancy and after delivery, to better understand problems such as premature birth and fetal death.
In the early days of pregnancy, the fertilized egg implants itself in the wall of the uterus and begins to divide a cell into many different types, some of which will form the placenta.
In one to two percent of pregnancies, some cells in the placenta have different chromosome numbers than cells in the fetus, a genetic defect that could be fatal to the fetus, but with which the placenta usually functions reasonably normally .
Despite this genetic robustness, placental problems are one of the main causes of damage to the mother and the fetus, such as growth retardation or even fetal death.
Parallelism with childhood tumors
Scientists from the Wellcome Sanger Institute and the University of Cambridge performed complete genome sequencing of 86 biopsies and 106 microdissections of 42 placentas, with samples taken from different areas of each organ.
The team found that each of these biopsies was a genetically distinct “clonal expansion,” indicating a clear parallel between the formation of the human placenta and the development of cancer.
The analysis also identified specific mutation patterns commonly found in childhood cancers, such as neuroblastoma and rhabdomyosarcoma, with even more of these mutations in the placenta than in the cancers themselves.
Professor Steve Charnock-Jones, lead author of the study from the University of Cambridge explains:
“Our study confirms for the first time that the placenta is organized differently from any other human organ, and indeed resembles a mosaic of tumors. The rates and patterns of genetic mutations were also incredibly high compared to other healthy human tissues. “.
The team found evidence to support the theory that the placenta tolerates major genetic failures, as another researcher Professor Gordon Smith notes:
“It was fascinating to observe how a genetic defect as serious as an error in the chromosomal copy number was corrected by the baby, but not by the placenta. This error would have been present in the fertilized egg. However, the derived cells that formed the child, they had the correct number of copies of chromosome 10, while parts of the placenta did not make this correction.
The placenta also warned that the baby had inherited both copies of the chromosome from one of the parents, which in itself can be associated with problems. “
Dr Sam Behjati, from the Wellcome Sanger Institute, adds the importance of further research with larger samples to discover the causes of complications and illnesses that arise during pregnancy.
“The placenta is like the ‘wild west’ of the human genome, completely different in its structure from any other healthy human tissue. It helps protect us from defects in our genetic code, but there is still a large burden of diseases associated with the placenta .
Our findings justify the study of the association between genetic imbalances in the placenta and problems in delivery on a large scale. “
Via | Wellcome Sanger Institute
Photos | iStock
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