Scientists at the Wolfson Institute for Biomedical Research of University College London, part-funded by the Biotechnology and Biological Sciences Research Council (BBSRC) and working with international collaborators, used a new genetic technique to tag embryonic stem cells and then trace them to the adult animal. They discovered that instead of homogeneous groups of stem cells making up the bones of the shoulder and neck and another making the muscles, a newly-discovered group of stem cells called mesenchymal stem cells make both the muscles and the point where it joins the skeleton.
The researchers believe their results show that the skeleton and muscles of vertebrates should not be seen as separate but instead are composites, with the boundaries between cell groups blurred around the body. For example, the stem cell group that makes the connective tissues of the swallowing/gulping muscles also makes the skeletal regions of the shoulder girdle. This sheds new light on human diseases such as Klippel-Feil syndrome where both regions are often malformed.
Dr Georgy Koentges, one of the lead researchers at UCL, said, "Anatomists and everyone else would look at the skeleton and assume that the bone structures are uniform and are the basic components of vertebrate organisation. 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. These groups of stem cells are making sca ffolds of connections early during embryonic development which are later embellished and filled by other cells: 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 ?normally without us noticing it."
As the joining points between muscles and bones have survived unaltered across hundreds of millions of year researchers can also start to map cell territories into fossils. For the first time the research team have been able to trace what happened to a major shoulder bone that features in many extinct land animals. They found that it appears to survive in modern vertebrates as the scapular spine.
Dr Koentges commented, "Now that we have identified these key players in forming the neck and the shoulders we can start looking for the genes that are on 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. This is an active area of research that we are involved in."