Study Gives Better Understanding of Spinal Diseases

The neck bone's connected to the shoulder bone, just like the song says. But British scientists have found genetic evidence that one set of stem cells actually builds both the bones and muscle of those key structures, offering a better understanding of how diseases in those areas develop and might be cured.

An international team of scientists led by researchers at University College London used a new genetic technique to mark embryonic stem cells and trace them into adult animals with spines.

They discovered a new group of stem cells, called mesenchymal stem cells, that makes both the muscles of the neck and shoulder and the tissue where muscle joins the skeleton.

That's contrary to conventional medical wisdom, which held that one type of stem cell makes bones and another makes muscle in a maturing animal.

"Anatomists and everyone else would look at the skeleton and assume that the bone structures are uniform and are the basic components of vertebrate organization," said Dr. Georgy Koentges, one of the lead researchers for the paper published Thursday in the journal Nature and a researcher at the university's Wolfson Institute for Biomedical Research.

"Our research suggests this is wrong, and actually groups of stem cells create not only the muscles of the neck and shoulder, but also the skeletal structure where these muscles are attached," Koentges added.

In the paper, the scientists argue that bones and muscles of animals should not be viewed as separate components, but rather as composite materials, with the boundaries between cell groups blurred throughout the body.

For instance, the stem-cell group that makes the connective tissues of the swallowing-gulping muscles also makes the skeletal regions of the shoulder girdle. One of the most primitive connections to the brain exists between those regions, and there are genetic diseases in humans where both regions are often malformed.

"These groups of stem cells are making scaffolds of connections early during embryonic development, which are later embellished and filled by other cells," Koentges said. "It's just like the scaffold of a house, which is later filled in by bricks, mortar and windows. If cells are from the same stem-cell origin, they 'stick together' throughout their life, usually without us noticing it."

The findings also may help scientists understand how backboned animals evolved, by seeing what structures at joining points have survived unaltered over hundreds of millions of years.

For instance, the team traced a major shoulder bone that is present in many extinct land animals and found that it's still present in modern vertebrates as the scapular spine.

"Now that we have found these key players forming the neck and shoulders, we can start looking for the genes that are active in these stem cells and which are ultimately responsible for evolutionary changes over millions of years and are also behind a number of serious human illnesses," Koentges said.

On the Net: www.nature.com