Of mice and men – differential mechanisms of maintaining the undifferentiated state in mESC and hESC

The persistence of the defining characteristics of undifferentiated cells in vivo and in vitro is maintained via a complex interplay of several mechanisms, employing molecular events internal to the cell as well as signals originating outside the cell. The exogenous and the endogenous mechanisms maintaining stemness qualities of the cell are intricately interwoven with one another and susceptible to cross-interference. Mice and rats as animal models are almost universally considered to be close enough to humans so as to be used in research and applications eventually intended for use in human biology and medicine, at the same time being related distantly enough from primates so as not to overstep ethical boundaries. Studying the specific molecular features of both species in the context of maintenance of the undifferentiated state of mESC and hESC can provide researchers with an unique opportunity to unravel the network of interactions which take part in the decision about cell fate under different conditions; to glean interesting insights into the parallel evolution of the two species and to observe how different variants of basic cellular processes have been tried and tested in the evolutionary process. The present paper reviews the basic signalling pathways responsible for the maintenance of the undifferentiated state in mESC and hESC and analyses some specific aspects of the molecular physiology that are unique to the particular species