First ever map of human limb development looks like an artist’s masterpiece

Scientists have shared unprecedented insights into human development with a world-first map that shows how limbs grow in the womb.

Human fingers and toes do not grow outward; instead, they form from within a larger foundational bud, with cells receding to reveal the digits beneath.

After around seven weeks of cell development, an ‘orchestrated cell death’ finally unveils the shapes of fingers or toes.

This is among many processes captured visually for the first time as scientists unveil a map of entire developing human limbs.

A dye that stains the tissue revealed clearly how cells arrange themselves into patterns of the forming digits.

This research could change how doctors diagnose and treat muscle-related disorders and congenital limb syndromes, like extra fingers and toes.

In the study, which is part of the Human Cell Atlas initiative to map every cell type in the human body, scientists applied cutting-edge technologies to create a map that pinpoints the exact location of cells of the early human limb.

The atlas, created by researchers at the Wellcome Sanger Institute, Sun Yat-sen University and EMBL’s European Bioinformatics Institute, is the first to capture the intricate processes governing the limbs’ rapid development during the early stages of limb formation.

Limbs are known to initially emerge as undifferentiated cell pouches on the sides of the body, without a specific shape or function.

But after 8 weeks of development, they are clearly defined, anatomically complex and immediately recognisable as limbs, complete with fingers and toes.

This requires a rapid and precise orchestration of cells. Any small disturbances to this process can have an effect, which is why variations in the limbs are among the most frequently reported syndromes at birth, affecting approximately one in 500 births globally.

While limb development has been extensively studied in mouse and chick models, the extent to which they mirror the human situation remained unclear until now.

In this new study, scientists analysed tissues between 5 and 9 weeks of development. This allowed them to trace specific gene expression programs, activated at certain times and in specific areas, which shape forming limbs.

The team were also able to confirm that many aspects of limb development are shared between humans and mice.

Senior study author professor Hongbo Zhang said the map is a major breakthrough in the understanding of how human bodies form.

He explained: ‘What we reveal is a highly complex and precisely regulated process.

‘It’s like watching a sculptor at work, chiselling away at a block of marble to reveal a masterpiece. In this case, nature is the sculptor, and the result is the incredible complexity of our fingers and toes.’

Dr Sarah Teichmann, senior author of the study from the Wellcome Sanger Institute, and co-founder of the Human Cell Atlas, added: ‘For the first time, we have been able to capture the remarkable process of limb development down to single cell resolution in space and time.

‘Our work in the Human Cell Atlas is deepening our understanding of how anatomically complex structures from, helping us uncover the genetic and cellular processes behind healthy human development, with many implications for research and healthcare.’