Reprogramming cellular identity - historical introduction

The first lecture reviewed the history of cloning and reprogramming - starting with the germ plasm theory proposed at the end of the XIX th century by German biologists August Weismann and Wilhelm Roux. In essence, these researchers postulated that the germ cells that ensure the transmission of the species' characteristics must possess all the information contained in the fertilized egg nucleus. However, this information would be lost during somatic cell differentiation. This theory of embryonic development therefore implied a discontinuity between soma and germ line, and thus opposed Jean-Baptiste Lamarck's theory of the transmission of acquired traits. However, nuclear transfer cloning experiments in the 1950s and 1960s demonstrated that somatic cell differentiation is a reversible process, since a whole animal could be obtained from a somatic cell nucleus. In other words, this work established that differentiation results from the differential expression of genes rather than their elimination during successive cell divisions. The lecture recalled that, of course, examples of natural cloning abound in the plant kingdom, particularly in grapevines. We then described the many attempts at cloning in different mammalian species, as well as potential applications and ethical limitations in humans. Emphasis was placed on the discovery and manipulation of embryonic stem cells in mice, which paved the way for obtaining the first induced pluripotent stem cells from somatic cells.