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An experiment to determine what it would take to achieve limb regeneration in humans

Image credit: Yang Yang, Bei Liu, et al.

Darko Savic
Darko Savic Sep 13, 2021
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The idea is to create two different sets of human-animal chimeras, amputate both and compare the gene expression of human cells found in the amputation spot. The identified differences hint at the necessary conditions if human limb regeneration was to become a reality.

The two chimeras:
  • axolotl blastocyst (host) + human pluripotent stem cells
  • mouse blastocyst (host) + human pluripotent stem cells
Axolotls are known for their ability to fully regenerate parts of their body after amputation.

The experiment
  1. Amputate a limb in both adult chimeras and look for human cells at the amputation spot (limb bud blastema).
  2. The mouse-human chimera serves as a control in this experiment. This is because neither species has regeneration capabilities in adulthood.
  3. The axolotl-human chimera would hopefully retain the regeneration capability and grow a new limb.
  4. Do a side by side comparison of gene expression and other "omics", especially epigenomics.
  5. The result hints at what conditions need to be present for human limb regeneration.
This could work because cells do what adjacent cells do. The environment determines the action. Axolotl cells regenerate. The human cells that are nearby get the same biochemical instructions and thereby activate their own suitable/matching genes (if they have them).

Inter-species chimeras

Three days after fertilization, a developing embryo contains about 6 to 10 cells. By the fifth or sixth day, the fertilized egg is known as a blastocyst — a rapidly dividing ball of cells. The inner group of cells will become the embryo. The outer group will become the cells that nourish and protect it.

An inter-species chimera is formed by injecting pluripotent stem cells from another species into the blastocyst and then returning the blastocyst into the uterus of a pregnant foster mother of the same species.

Creation of human-animal chimeras is not a new concept. Human pluripotent stem cells have been used to create chimeric embryos in rodent hosts.

[1]James D, Noggle SA, Swigut T, Brivanlou AH: Contribution of human embryonic stem cells to mouse blastocysts. Dev Biol 2006;295:90-102.

[2]Freedman B, S: Hopes and Difficulties for Blastocyst Complementation. Nephron 2018;138:42-47. doi: 10.1159/000480370

[3]Mascetti VL, Pedersen RA: Human-mouse chimerism validates human stem cell pluripotency. Cell Stem Cell 2016;18:67-72.

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