Before the key points of development, the animal was unable to close the wounds created by the amputation, and half of the two embryos simply spewed cells into the environment. However, some later, there was excellent survival, and the embryo’s head could regenerate the tail. This indicates that the normal signaling pathways present in the embryo are sufficient to advance the process.
However, the embryo tail at this stage does not seem to be able to reconstruct the head. However, researchers discovered that these posterior fragments could inhibit WNT signaling, which was sufficient for the brain to develop.
Muscle shortage
One possibility here is that at this point Wnt signaling is widely active in the posterior part of the embryo, blocking the formation of anterior structures. Alternatively, researchers assume that the problem is usually in muscle cells that help organize the formation of stem cell-filled blasts needed to begin the regenerative process. Because the anterior end of the embryo develops faster, it suggests that there may not be enough muscle cells in the tail to kick off this process at the early stages of development.
To test their hypotheses, they performed a somewhat unusual experiment. They started by cutting off the tail of the embryo and saving 24 hours. At that point, they cut the front end from the tail and create a new wound to heal. At this point, regeneration proceeded as normal, with the tail growing a new head. This is not conclusive evidence that muscle cells are missing in the early stages, but it shows that after the initial cut, several important developmental steps occur in the tail in the window for 24 hours.
The results reinforce the idea that regeneration of major body parts requires the reestablishment of signals laying out the organization of the developing embryo. These signals are complicated when they are currently working to organize the embryo. And it clearly shows that the cells needed to perform this reorganization were not only aside early in development, but also take time to emerge. All that information helps clarify the larger problem of painting as to how these animals manage such a complex regeneration process.
Current Biology, 2025. doi: 10.1016/j.cub.2025.03.065 (About DOI).
