Characterization of pluripotency genes in axolotl spinal cord regeneration

Regeneration is a process that renews damaged or lost cells, tissues, or even of entire body structures, and is a phenomenon which is widespread in the animal kingdom. Urodeles such as newts and salamanders have a remarkable regeneration ability. They can regenerate organs such as gills, lower jaws, retina, appendages like fore- and hind limbs, and also the tail including the spinal cord. The regeneration process requires the use of resident stem cells or somatic cells, which have to be reprogrammed. In both cases the reprogrammed cells are less differentiated, meaning the cell would have the ability to form any kind of fetal or adult cell which rose from the three different germ layers, the ectoderm, mesoderm and endoderm. Artificial reprogramming of differentiated mammalian somatic cell had been reported previously. It was shown that four pluripotency factors, OCT4 (also called POU5f1), SOX2, c-MYC and KLF4 are sufficient to generate an induced pluripotent stem (iPS) cell. It has been shown that some of these factors are also involved in regenerating processes. In newt limb and lens tissue, Sox2, c-Myc and Klf4 mRNA levels were upregulated in the beginning of blastema formation when compared to non-amputated tissue. Oct4 mRNA however, was not detected. During xenopus tail regeneration, Sox2 and c-Myc were expressed, while the xenopus Pou homologs Pou25, Pou60, Pou79, Pou91 were not detected. In regenerating zebrafish fin tissue, Sox2, Pou2, c-Myc and Klf4 mRNA were not upregulated. The mammalian transcription factor OCT4, a class V POU protein, is responsible in maintaining pluripotency in gastrula stage embryos. It was reported that mouse OCT4 is also expressed in the caudal node of embryos having 16 somites. It is further known that progenitors exist in mouse tailbud, which give rise to neural and mesodermal cell lineage. This suggests that the OCT4 expressing cells in caudal node might be a stem cell reservoir. Oct4 was detected in axolotl during embryonic deve