Abstract
Review of key points from previous lesson. History of the T locus and cloning of the Tbxt gene. Potential importance of this gene in tail loss in hominids, following an exon skipping phenomenon specific to humans and apes.
This second lesson begins with a brief review of some of the key points developed in lesson 1, concerning in particular the splicing phenomenon and the basis of tail development in mammals. Next, the history of the Tlocus is summarized, from the first short-tailed mice obtained by irradiation at the Institut Curie in Paris in the 1920s, to the cloning of the gene (Tbxt) at the turn of the millennium, an eventful history that took in the USA before returning to the Institut Pasteur, which illustrates both the birth of mouse genetics, and the fundamental epistemological differences between developmental biology ( classic ), on the one hand (causal embryology), and the genetic approach to development, on the other.
This lesson then focuses on the study of a recent publication implicating this Tbxtgene in the loss of the tail in great apes, some 25 million years ago. The possible cause is the insertion of a small repeat sequence that induces exon skipping and thus the production of a protein slightly shorter than the normal protein, which is nevertheless still present, in the same quantity as the small protein. What are the mechanisms involved in translating this small genetic variation into a variation in tail length ? And how could this simple genetic event, the addition of a tiny DNA fragment, have led to an evolutionary transformation of such magnitude and stability that the outright disappearance of this useful structure ?
