Vertebrate Embryo: Neural Patterning

Abstract

Neural patterning is the process of providing regional identities in neural cells in accordance with their location in the neural tube. Allocation of regional identities is prerequiscent for the following processes of neuronal circuit formation. The neural tube is longitudinal among the body axis thus having anterior–posterior polarity (rostral–caudal in aves, future superior–inferior in adult human). It also has dorsal–ventral polarity and right and left sides. Neural patterning commences as the neural induction takes place progressively in the anterior to posterior direction. By signalling and tissue interaction, the neural tube is divided into the forebrain, midbrain, hindbrain and the spinal cord along the anterior–posterior axis. Further divisions follow to produce differentiation of functional compartments that are defined by the combinatorial expression of molecular markers. The same principle, the initial subdivision by signalling followed by refined compartmentalisation, applies to the acquisition of dorsal–ventral specification as well.

Key Concept

  • Depending on the actual position in the body, cells are specified with respect to the position (positional specification), thus positional identity is acquired. Cells then interpret their positions to differentiate accordingly, thus spatial patterns are formed (see Wolpert, 2011).
  • Neural patterning is the process through which neural progenitors acquire positional identities. The initial allocation of positional information is governed by signalling mechanisms. This is followed by expression of transcription factors, such as Hox genes for the anterior–posterior axis.

Keywords: anterior–posterior; Hox genes; retinoids; fibroblast growth factors; Wnt; dorsal–ventral; BMP (bone morphogenetic protein); Shh (sonic hedgehog)

Figure 1. A–P patterning of the CNS. The scheme is based on chick development. D, dorsal; V, ventral. The first 4–5 somites, called occipital somites, are incorporated into head structures.
Figure 2. Examples of Hox expression in chick embryos revealed by in situ hybridisation with ribonucleic acid (RNA) probes. (a) Hoxb1; (b) Hoxb4; (c) Hoxb9. Arrows indicate anterior‐most boundary of expression in the neural tube: (a) at rhombomere 4, (b) at rhombomere 6/7 boundary, in (c) the somite level 12–13. Most Hox genes show continuous expression in the neural tube and in somites, the latter of which is at more posterior levels. With regard to Hoxb1, the expression is initially seen posterior to rhombomere 4 (inclusive) at early stages; however, the expression domain in the neural tube is split into two: one restricted to rhombomere 4 and another posterior to rhombomere 6/7 boundary, as seen in (a).
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Further Reading

Gilbert SF (2013) Developmental Biology, 10th edn. Chapter 8, Early development in vertebrates: Amphibians and fish; Chapter 9, Early development in vertebrates: Birds and Mammals Boston, MA: Sinauer Associates.

Slack J (2012) Essential Developmental Biology, 3rd edn. Chichester, UK: Wiley‐Blackwell.

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How to Cite close
Itasaki, Nobue(Feb 2015) Vertebrate Embryo: Neural Patterning. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0000737.pub3]