Every pregnant woman knows that her waters breaking are a definite sign a baby is coming. Up until then a bag of nourishing chemicals, known as the amniotic sac, surrounds the new life. The sac bursts just before labour, but how it first develops is a little mysterious. Grown in a dish from human pluripotent stem cells, this 'embryoid' mimics cellular changes that happen when an embryo first implants in the womb. Cells (with their nuclei stained blue) organise themselves into a hollow ball shape called a cyst. The red-coloured cells are using a tell-tale embryonic gene called Oct4 – similar cells in the womb contribute to the embryo itself. At the top of the cyst (with its inner surface stained green) cells form a tough skin of amnion, defining the shape of the amniotic sac and producing a model that scientists can use to study development and fertility.
Written by John Ankers
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