These delicate floating footballs are mouse embryos – microscopic balls of cells just four-days old. But even at this early stage, there are key differences between clusters of cells. These embryos have been stained with fluorescently-labelled markers that highlight cells with different fates. The blue cells will become part of the placenta, the organ that connects a developing foetus with its mother, while the pink cells will form the protective yolk sac around it. But perhaps the most interesting cells are the white ones. These have the potential to form any kind of cell, from lung to liver and skin to stomach, and will go on to make all the tissues required to grow a baby mouse. By studying mouse embryos like this, scientists can get a glimpse at the biological processes at work at the very earliest stages of life, which are relevant to human baby-making too.
Written by Kat Arney
BPoD stands for Biomedical Picture of the Day. Managed by the MRC London Institute of Medical Sciences the website aims to engage everyone, young and old, in the wonders of biomedicine. Images are kindly provided for inclusion on this website through the generosity of scientists across the globe.