The mammalian brain is characterised by the development of a vast neocortex that is superposed to the ancien ‘reptilian’ paleocortex. This distinction derives from how neurones are made: by direct neurogenesis in the paleocortex, and by indirect neurogenesis in the neocortex. But how different parts of the brain decide which developmental mechanism to use? A team of researchers lead by Victor Borrell at the Neuroscience Institute in Alicante (Spain) in collaboration with American and German researchers, as well as SIB scientist Athanasia Tzika in the Department of Genetics and Evolution of the University of Geneva, has discovered that the control of the direct versus indirect neurogenesis depends only on the expression of three genes. To test their hypothesis, the scientists have inverted the process: generating mammalian cortical tissues in the snake and reptilian tissue in the mouse ! These results, published today in the journal Cell, open a new era in our understanding of the development and evolution of the brain.

wheat snake embryo
Corn snake embryo (Pantherophis guttatus) 10 days after laying (experiments on brain development were conducted at earlier stages: between 4 and 6 days after egg laying) - © Athanasia Tzika (UNIGE / SIB)


Cárdenas et al. Evolution of cortical neurogenesis in amniotes controlled by Robo signaling levels. Cell. DOI: