Mesenchymal phenotype as a hallmark of undifferentiated states

The mesenchymal phenotype has long been related to either the structural support or the transition between two subsequent epithelial stages. Although this view is generally correct in certain contexts of embryonic development as well as of adult anatomy, it has been challenged by recent advances from convergent fields of research that showed how the presence of mesenchymal traits may hallmark states of intrinsic plasticity and stem cell identity both in physiological and pathological contexts. Following this line, the present review summarizes studies that support the hypothesis that the partially or fully mesenchymal phenotype might represent a general paradigm of stem cell plasticity underlying embryonic development, regenerative potential as well as their pathological counterparts.