Researchers discover bone growth in unborn babies

How do the embryo's bones actually form? British scientists studied this issue. The result is a unique recording.

Melanie Lanno/t-online

A team of researchers has decoded exactly how an unborn baby's bones form and grow, right down to the individual cells. Scientists led by Ken To of the Wellcome Sanger Institute in the UK recently published their findings in the prestigious journal Nature.

From fertilized egg to bone

Our lives all begin with a fertilized egg. But how all cell types, tissues and organs arise from such cells was previously only partially understood. Now, researchers have created a “cellular atlas” of human bone formation that shows how specific genes form bone and how they interact.

In their study, the scientists analyzed tissue samples from embryos in the first trimester of pregnancy (about five to 11 weeks after fertilization). They identified the active genes and their so-called epigenetic marks in every cell in the site where children's bones and skulls are formed.

Cartilage is the precursor of bone

The results are fascinating: Human bone formation begins around six to eight weeks after fertilization—right around the time an embryo becomes a fetus. In the limbs, chondrocytes initially serve as “guides” and framework for bone development. Beginning in the eighth week of pregnancy, this cartilage framework is gradually replaced by bone tissue.

Embryonic arms: First cartilage cells form, then bones.Image: K. To, L. Fei, JP Pett et al./Nature (2024)

Study author Ken To explains:

This also revealed some previously unknown cell types and signaling pathways as well as differences in mouse bone development.

Special Development of the Skull

However, the development of the skull is different from that of the rest of the bones: there is no preliminary framework for the formation of cartilage cells on top of the skull. Instead, osteoblasts multiply directly in the membrane covering the child's skull. These bony precursors emerge at the edges of the later frontal and parietal bones, causing these areas to gradually ossify while the cranial sutures remain soft. This mechanism is crucial to ensuring that the brain has enough room to grow.

Embryonic skull: Its bones (purple) form directly without any previous cartilage framework.Photo: A.Chédotal & R. Blain/Institut de la Vision, Paris & MeLiS/UCBL/HCL, Lyon

Drugs damage embryonic bones

The team also looked at how 65 common drugs affected the embryo's bone development. Pregnant women should avoid certain medications because they may cause birth defects. “Our analysis can now identify bone cell lines whose gene activity is altered by these teratogens.”“, To and colleagues report. Thanks to these new findings, drugs can be tested more specifically for their side effects, making them safer.

The study authors are convinced that the new cell atlas represents an important tool for future medical research. In addition to bones, other organs have also been mapped: among them are components of the digestive system, parts of the brain and the immune system. A total of 40 professional articles have been published on the current status of this mapping.

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