Embryo development: Some cells are more equal than others even at four-cell stage
Although they seem to be identical, the cells of a two-day-old embryo are already beginning to display subtle differences
Genetic ‘signatures’ of early-stage embryos confirm that our development begins to take shape as early as the second day after conception, when we are a mere four cells in size, according to new research led by the University of Cambridge and EMBL-EBI.
Once an egg has been fertilised by a sperm, it divides several times, becoming a large free-floating ball of stem cells. At first, these stem cells are ‘totipotent’, the state at which a stem cell can divide and grow and produce everything — every single cell of the whole body and the placenta, to attach the embryo to the mother’s womb. The stem cells then change to a ‘pluripotent’ state, in which their development is restricted to generating the cells of the whole body, but not the placenta. However, the point during development at which cells begin to show a preference for becoming a specific cell type is unclear.
Now, in a study published in the journal Cell, scientists at the University of Cambridge, the European Bioinformatics Institute (EMBL-EBI) and the Wellcome Trust Sanger Institute suggests that as early as the four-cell embryo stage, the cells are different.
The researchers used the latest sequencing technologies to model embryo development in mice, looking at the activity of individual genes at a single cell level. They showed that some genes in each of the four cells behaved differently. The activity of one gene in particular, Sox21, differed the most between cells; this gene forms part of the ‘pluripotency network’. The team found when this gene’s activity was reduced, the activity of a master regulator that directs cells to develop into the placenta increased.
“We know that life starts when a sperm fertilises an egg, but we’re interested in when the important decisions that determine our future development occur. We now know that even as early as the four-stage embryo – just two days after fertilisation – the embryo is being guided in a particular direction and its cells are no longer identical.”
Professor Magdalena Zernicka-Goetz from the Department of Physiology Development and Neuroscience at the University of Cambridge
“We can make use of powerful sequencing tools to deepen our understanding of the molecular mechanisms that drive development in individual cells. Because of these high-resolution techniques, we are now able to see the genetic and epigenetic signatures that indicate the direction in which early embryonic cells will tend to travel.”
Dr John Marioni of EMBL-EBI The Wellcome Trust Sanger Institute and the Cancer Research UK Cambridge Institute
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Notes to Editor
The research was funded by the Wellcome Trust, the European Molecular Biology Laboratory, and Cancer Research UK
The mission of the University of Cambridge is to contribute to society through the pursuit of education, learning and research at the highest international levels of excellence. To date, 90 affiliates of the University have won the Nobel Prize.
Founded in 1209, the University comprises 31 autonomous Colleges, which admit undergraduates and provide small-group tuition, and 150 departments, faculties and institutions.
Cambridge is a global university. Its 19,000 student body includes 3,700 international students from 120 countries. Cambridge researchers collaborate with colleagues worldwide, and the University has established larger-scale partnerships in Asia, Africa and America.
The University sits at the heart of one of the world’s largest technology clusters. The ‘Cambridge Phenomenon’ has created 1,500 hi-tech companies, 14 of them valued at over US$1 billion and two at over US$10 billion. Cambridge promotes the interface between academia and business, and has a global reputation for innovation.
The Wellcome Trust Sanger Institute is one of the world’s leading genome centres. Through its ability to conduct research at scale, it is able to engage in bold and long-term exploratory projects that are designed to influence and empower medical science globally. Institute research findings, generated through its own research programmes and through its leading role in international consortia, are being used to develop new diagnostics and treatments for human disease.
The Wellcome Trust is a global charitable foundation dedicated to achieving extraordinary improvements in human and animal health. We support the brightest minds in biomedical research and the medical humanities. Our breadth of support includes public engagement, education and the application of research to improve health. We are independent of both political and commercial interests.
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