Contrary to mammalian DNA, which is thought to contain only 5-methylcytosine (m5C), bacterial DNA contains two additional methylated bases, namely N6-methyladenine (m6A), and N4-methylcytosine (m4C). However, if the main function of m5C and m4C in bacteria is protection against restriction enzymes, the roles of m6A are multiple and include, for example, the regulation of virulence and the control of many bacterial DNA functions such as the replication, repair, expression and transposition of DNA. Interestingly, even if adenine methylation is usually considered (...) a bacterial DNA feature, the presence of m6A has been found in protist and plant DNAs. Furthermore, indirect evidence suggests the presence of m6A in mammal DNA, raising the possibility that this base has remained undetected due to the low sensitivity of the analytical methods used. This highlights the importance of considering m6A as the sixth element of DNA. BioEssays 28: 309–315, 2006. © 2006 Wiley Periodicals, Inc. (shrink)

The characterisation of normal stem cells and cancer stem cells uses the same paradigm. These cells are isolated by a fluorescence‐activated cell sorting step and their stemness is assayed following implantation into animals. However, differences exist between these two kinds of stem cells. Therefore, the translation of the experimental procedures used for normal stem cell isolation into the research field of cancer stem cells is a potential source of artefacts. In addition, normal stem cell therapy has the objective of regenerating (...) a tissue, while cancer stem cell‐centred therapy seeks the destruction of the cancer tissue. Taking these differences into account is critical for anticipating problems that might arise in cancer stem cell‐centred therapy and for upgrading the cancer stem cell paradigm accordingly. (shrink)