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Placenta development occurs before a fertilised egg divides

28 September 2020
Appeared in BioNews 1065

Placenta development is initiated first in human pregnancies, even before the embryo starts to form, according to new research.

A team of scientists at the Francis Crick Institute, London, has found that one of the first steps after egg fertilisation in mammals is the initiation of placenta creation, the organ responsible for providing oxygen and nutrients to the growing baby.

'This study highlights the critical importance of the placenta for healthy human development,' said Dr Kathy Niakan, senior author of the study and group leader at the Crick. 'If the molecular mechanism we discovered for this first cell decision in humans is not appropriately established, this will have significant negative consequences for the development of the embryo and its ability to successfully implant in the womb.'

Once an egg is fertilised the cell rapidly divides and a key process called cell specialisation occurs, where each cell is assigned a specific task. The team sought to examine the very first cell specialisations by studying donated human embryos that were surplus to in vitro fertilisation (IVF) treatment. In embryos at the 16-32 cell stage, the team observed a subset of cells which changed shape and polarised, this triggered molecular events that drives placenta specialisation. In particular, atypical protein kinase C (aPKC) was highly expressed at one end of the cell, when aPKC was inhibited the cells no longer became placenta precursors.

This first cell specification is 'widespread in mammals' said researchers after they found the same result in cow and mouse embryos, which have divergent mechanisms at later stages of development.

This research, published in Nature, revealed that placenta development starts much earlier than previously thought, before the embryo has implanted into the wall of the uterus, suggesting placenta cells may have important functions in healthy embryo implantation and development.

During IVF treatment, a reliable predictor of successful implantation of an embryo is the presence of placental precursor cells under the microscope. Therefore, this work paves the way towards a better understanding of how to help those struggling to conceive.

'Understanding the process of early human development in the womb could provide us with insights that may lead to improvements in IVF success rates in the future' adds Dr Niakan, 'It could also allow us to understand early placental dysfunctions that can pose a risk to human health later in pregnancy.'

SOURCES & REFERENCES
Identification of key step in embryo development offers fertility treatment hope
Evening Express |  23 September 2020
Initiation of a conserved trophectoderm program in human, cow and mouse embryos
Nature |  23 September 2020
Placenta is initiated first, as cells of a fertilised egg divide and specialise
Francis Crick Institute |  23 September 2020
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