[Morphologic plasticity as a component of cognition]

Two recent developmental genetics studies suggest an important role for transcription factors of the homeodomain protein class in the morphogenesis of cerebral structures and the form and extent of the various domains that constitute the nervous system (Krumlauf, 1994; Rubenstein and Puelles, 1994). Our team recently took a look at the hypothesis that the same transcription parameters have a function in axonal growth and recognition of paths and targets. It has been shown that cortical or spinal medullary neurons are capable of responding, by a change in axonal growth rate, to regulation of the activity of certain transcription factors (Prochiantz and Théodore, 1995). This demonstration was facilitated by a particular property of the DNA binding region of the transcription factors. This property consists in crossing plasmic membranes and addressing cell nuclei directly (Prochiantz, 1996). The homeodomain proteins are expressed not only during development but also in adulthood. It is possible that their continuous expression or reactivation may be associated with the morphological changes in neurons observed in the mature nervous system. The latter hypothesis will be discussed on the basis of our current knowledge of the expression and role of the transcription factors. The authors will draw some conclusions regarding the possibility of considering these nuclear factors as agents of cerebral plasticity and as targets of potential pharmacological value.