Neural induction and early patterning in vertebrates

Abstract

In vertebrates, the development of the nervous system is triggered by signals from a powerful 'organizing' region of the early embryo during gastrulation. This phenomenon--neural induction--was originally discovered and given conceptual definition by experimental embryologists working with amphibian embryos. Work on the molecular circuitry underlying neural induction, also in the same model system, demonstrated that elimination of ongoing transforming growth factor-β (TGFβ) signaling in the ectoderm is the hallmark of anterior neural-fate acquisition. This observation is the basis of the 'default' model of neural induction. Endogenous neural inducers are secreted proteins that act to inhibit TGFβ ligands in the dorsal ectoderm. In the ventral ectoderm, where the signaling ligands escape the inhibitors, a non-neural fate is induced. Inhibition of the TGFβ pathway has now been demonstrated to be sufficient to directly induce neural fate in mammalian embryos as well as pluripotent mouse and human embryonic stem cells. Hence the molecular process that delineates neural from non-neural ectoderm is conserved across a broad range of organisms in the evolutionary tree. The availability of embryonic stem cells from mouse, primates, and humans will facilitate further understanding of the role of signaling pathways and their downstream mediators in neural induction in vertebrate embryos.

Neural specificity of the RNA-binding protein Elav is achieved by post-transcriptional repression in non-neural tissues

“…For example, loss of the miRNA pathway might reveal a default neural program, which was reported as the ground differentiation state of the vertebrate ectoderm (Chang and Hemmati-Brivanlou, 1998;Ozair et al, 2013). Curiously, Mei-P26 is another factor with specific (although not exclusive) neural expression that is derepressed in non-neuronal miRNA pathway mutant clones (Herranz et al, 2010).…”

Embryoids, organoids and gastruloids: new approaches to understanding embryogenesis

“…The grafted cells contributed to axial mesodermal derivatives (such as the notochord), whereas the nervous system (with the exception of the floor plate) was derived from the host. Importantly, this experiment established that symmetry breaking is caused by localized inductive signals (Ozair et al, 2013;Spemann and Mangold, 1924). In asking how early these symmetry-breaking signals are established, it was shown that two to three blastomeres of an eight-cell stage Xenopus embryo are sufficient to give rise to a second body axis when transplanted into a 64-cell embryo (Gimlich and Gerhart, 1984).…”

Oxygen Tension Within the Neurogenic Niche Regulates Dopaminergic Neurogenesis in the Developing Midbrain

“…T he central nervous system originates from a small number of cells proliferating during early development from the neural plate [1], which reaches a number of hundreds of billions neurons in higher mammals [2]. This process named neurogenesis involves cell division, migration, differentiation, and interaction of cells to form an extremely dynamic, functional network.…”