Reacción a "Reactions: scientists regenerate neural pathways in mice with rat cells"

No cause for concern but cause for amazement. We have known for many years that cells injected into blastocysts can repair an organism. Now this has been confirmed by experimentally produced organ defects. It is hardly surprising that this also applies to the brain. However, it is quite astonishing that neuronal cells are extremely plastic and support organogenesis across species boundaries, including in the brain. Here we need to revise our understanding of genetics and species boundaries in favor of a greater significance of cellular plasticity in the formation of organs.

Chimeras allow us to study the interaction of different cells through markers. This is extremely helpful for describing developmental processes in organ formation. In these xenological studies on the brain, it becomes clear that neuronal cells can also correspond with each other across species boundaries and form functional networks. The fact that they adapt their repair program depending on the conditions (cells sick but present, cells eliminated) was previously unknown. In this respect, these studies will provide important findings for therapeutic approaches. Whether only the findings or even cells will actually be used for this purpose cannot be estimated at present.

In principle, such experiments are also possible between other species. However, we already know from other organ systems that regenerative processes are not arbitrarily interchangeable. For example, testicular stem cells from rats can generate sperm in the testicles of mice, but primate stem cells cannot. Although they settle, they do not differentiate and remain as stem cells in the mouse testis. It will be exciting to study the different organ systems and learn which processes are more conserved and allow interspecies communication and interaction.

For ethical reasons, caution seems to be called for here. While blastocyst complementation opens up a highly interesting field for basic research, the generation of organ replacements for clinical applications is not a realistic scenario. There still appears to be far too little knowledge about species- and organ-specific effects to be able to assess the risks. As with cloning, there should be an internationally recognized moratorium here.