The reversibility of cellular determination: An evolutive pattern of epigenetic plasticity

Until the middle of the 20th century, embryogenesis patterns were considered as based on a rigid, unidirectional ontogenetic development, whose nuclear programming yields an irreversibility feature for cellular determination. Further empirical pieces of evidence have provided new insights about a certain reversibility to cellular determination, finding new biomolecular mechanisms (nuclear reprogramming, dedifferentiation, transdifferentiation) which have clearly shown that such a reversibility exists, warranting a certain cellular plasticity inside cell cycle; moreover, they seem mainly ruled by epigenetic factors. In this framework, evolution can be viewed as a systemic transformation of the spatiotemporal epigenetic organization, and the maintenance of the stable final adult stage includes a possibility of dedifferentiation at the particular points of ontogenetic development leading to the achievement of the final stage though the alternate sets of epigenetic trajectories. This paper is aimed to briefly outline historically the main aspects which have led to define the mechanisms of cellular plasticity, highlighting the chief empirical facts supporting it and the related still unresolved problematic issues.