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This Way Up
13 January 2012

This Way Up

All complex animals have a head and a tail or, to put it more correctly, an anterior [top] end and a posterior [bottom]. This is set up at a very early stage in development, when the animal is just a little ball of cells. Three different views of a mouse embryo at this stage – made with a high-powered laser microscope – show individual cells stained with a dye that fluoresces blue under laser light. One of the key players in distinguishing where the head forms is a small group of cells called the anterior visceral endoderm (AVE), highlighted here in green. It's important that the AVE stays at the head end, so to ensure this happens, new cells (dyed red) are made mainly in the middle of the embryo. This keeps the AVE in the right place and out of the way of any confusing ‘tail’ signals.

Written by Kat Arney

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BPoD stands for Biomedical Picture of the Day. Managed by the MRC Laboratory of Medical Sciences until Jul 2023, it is now run independently by a dedicated team of scientists and writers. The website aims to engage everyone, young and old, in the wonders of biology, and its influence on medicine. The ever-growing archive of more than 4000 research images documents over a decade of progress. Explore the collection and see what you discover. Images are kindly provided for inclusion on this website through the generosity of scientists across the globe.

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