Scientists grow ‘antlers’ on mice in regenerative stem cell study
Lower vertebrates, like reptiles and fish, have shown a remarkable capacity to heal in a scar-free manner and regenerate lost appendages, even at the adult stage. However, most mammals have lost the ability to regenerate lost appendages or organs. A notable exception to this trend, though, is the antlers of deer. Scientists see this as a valuable model for studying organ regeneration in mammals. In their study, Qin et al. used stem cells to generate antlers on mice.
The first step for these researchers was to use RNA sequencing to examine nearly 75,000 cells from the antlers and nearby tissue of sika deer. The cells they looked at came from before, during, and after the antlers were lost, and the researchers were able to identify a specific family of stem cells that were key to antler renewal.
When looking at antlers 10 days before they were shed, the scientists identified a subtype of these stem cells abundantly seen in the stumps that remain on the day of shedding. By the fifth day before shedding, these cells had also generated a separate subtype of the stem cell; by the tenth day, this new subtype of stem cells had begun to develop into cartilage and bone cells.
The cell population at the five-day mark had the properties that the researchers were looking for. These cell masses, through migration and proliferation, move to the spot of the injury and have the information required for the animal to regenerate a missing organ or appendage. These cells were compared to other animals' regenerative cells (from mouse regenerative digit tips, axolotl limbs, and zebrafish caudal fins), and found that even though cell composition varied across species, a similar type of cell was present across them all: PRRX1+.
After examining these cells, the team of researchers transplanted day-five stem cells into the foreheads of mice. Within 45 days, the mice began growing antler-like structures that consisted of cartilage and bone. The researchers had also transplanted some day-zero stem cells into a group of mice, but they only generated fibrous connective tissue and not antlers.
At the end of the paper, the scientists conclude that antler regeneration is consistent with a conceptual stem cell-based regenerative process. They also note that their results suggest that these cells may have an application in clinical bone repair. They close their paper with the suggestion that the induction of human cells into those similar to the stem cells observed in this study could be used in regenerative medicine for skeletal injuries or limb regeneration.