The scientists belonging to Thomas Braun's working group used as a basis for their research two cell lines of mesenchymal stem cells which had been isolated from the bone marrow of mice. What was particularly special about the process they used was that they did not add growth factors to the culture medium; the goal was to prevent the cells from differentiating prematurely. By doing so, the scientists discovered that the two cell lines were different in the expression of typical stem cell markers. The researchers thus suspect that mesenchymal stem cells are a heterogeneous group of various, different cells, that have similar characteristics.
As was hoped, the scientists, using certain substances, were able to bring the stem cell line to express proteins characteristic of muscle cells. Interestingly, when a particular path, known as the wnt-signal path, was stimulated, the cells began to develop the features of heart muscle cells. In contrast, when they were beforehand stimulated with a protein known as CDO, the cells showed certain characteristics of skeleton muscle cells.
In both experiments, a row of muscle-specific genes was activated in the cells. This provided evidence for the beginnings of a differentiation process. But this process was only apparently halfway complete. So, for example, after the activation of the wnt-sign