Mice [15] (JM Cheverud et al., manuscript in preparation). This has al…

Mice [15] (JM Cheverud et al., manuscript in preparation). This has allowed a more focused analysis of candidate genes. Further narrowing ofArthur and Heber-Katz Stem Cell Research Therapy 2011, 2:30 http://stemcellres.com/content/2/3/Page 2 ofthese PubMed ID:https://www.ncbi.nlm.nih.gov/pubmed/14960617 loci and testing of candidates using gene knockouts should lead to the final identification of these genes. Besides ear hole closure, multiple organ and injury systems have extended the MRL mouse's unusual healing properties. They include regenerative studies s40337-016-0117-z in the heart [19-21], central nervous system stem cells and tissue [22-24], cartilage [25], cornea [26], digit [27,28] and myometrial healing [29]. Dorsal skin wound healing, which involves skin contracture, has been reported to be no different or even worse in the MRL compared to controls [30,31]. However, a recent study shows that if the wound has a syngeneic or allogenic skin transplant, the MRL shows far better healing than the control [32]. One possible explanation for the healing differences in different systems is that wound contracture, involving myofibroblasts or cells expressing Sma-1 (smooth muscle actin), known to 1-(4-Bromo-2-pyridyl)piperazine be responsible for scarring, is different in the MRL. Preliminary studies suggest this [33] (D Gourevitch, K Bedelbaeva, unpublished data). Thus, the wound site and type of wound need to be considered in the MRL's healing properties.G2/M cell cycle accumulation of regenerating cells The cells derived from the ear of regenerating and nonregenerating mice also show significant differences from each other and represent what is seen in vivo. MRL fibroblast-like cells from uninjured ears display an uncommon metabolic profile characteristic of an embryonic-type aerobic glycolysis, a feature of the adult MRL mouse itself, versus the more common metabolic state - oxidative phosphorylation - as seen in the B6 mouse [34]. These cells express stem cell markers similar to adult MRL tissue that expresses these markers [34]. In a separate study, cells derived from the injured MRL ear blastema expressed stem cell markers as found in vivo [35] and displayed highly proliferative and migratory responses in vitro similar to human multipotential progenitor cells in this study [36]. The rapid growth rate of fibroblast-like cells from the uninjured MRL ear was noted early on and examination of cell cycle regulation comparing healer MRL to nonhealer B6 cells showed that the healer cells had an unusual accumulation of cells in G2/M [33]. A likely explanation of such G2/M accumulation or potential arrest PubMed ID:https://www.ncbi.nlm.nih.gov/pubmed/13485127 was a DNA damage response and this was supported by an increased p53 response in the MRL [33] and confirmed with data showing that foci of H2AX and TopBP1, a phosphorylated histone and a protein recruited to sites of DNA damage, respectively, were highly increased in MRL cells and tissue [33]. DNA damage itself was tested using the comet assay and found in nearly 90 of healer cells compared to 5 of non-healer Methyl 2-((4-nitro-1h-pyrazol-1-yl)methyl)benzoate cells, showing both single-strand and double-strand breaks. Furthermore, the DNA repair protein RADwas increased in healer cells, suggesting that error-free homologous recombination was being used [33]. The cause of the DNA damage is still unclear, but the lack of the cell cycle protein p21Cip1/Waf1 discussed below suggests a replicative stress mechanism. These results agree with many reports in the literature that G2/M accumulation is associated with regeneration in examples ranging from hydra [37] to amphibian [38] to mammalian.