Cómo construir un tubo neural: la genética molecular del desarrollo neuroembriológico

Abstract

The 'new neuroembryology' combines classical morphogenesis with new molecular genetic data on the programming of neural differentiation and the interactions of transcription products of various developmental genes. The neuroepithelium is generated from the primitive (Hensen's) node in birds and mammals, homologous with the dorsal lip of the amphibian gastula. The developing neural placode is 'induced' by the notochord, which initiates the differentiation of the floor plate, a ventral midline ependyma. This induction is effected by a gene called Sonic hedgehog, which also is a strong ventralizing influence and induces motor neuron differentiation. Various families of genes program neural tube differentiation with dorsoventral or ventrodorsal gradients, rostrocaudal gradients and mediolateral gradients. Genes that establish the primordial axes of differentiation are 'organizer genes' and those involved with the identity of specific structures are 'regulatory genes'. Some developmental genes continue to be expressed in adult life and preserve the unique identity of specific cellular types. The neural tube is divided into compartments or segments known as neuromeres (or rhombomeres in the hindbrain) with physical and chemical barriers that limit cell migration between segments; the entire spinal cord is formed from rhombomere 8. Both extrinsic and intrinsic mechanical factors contribute to bend the neural placode to form the neural tube [REV NEUROL 1999; 28: 110-6].