Figure 1

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Figure 1. Polarized sources of inductive signals during spinal cord development. (A) Stages in the embryonic development of the spinal cord: The neural plate is generated as a columnar epithelium and is underlain by axial mesoderm cells of the notochord (N), and paraxial mesoderm (later the somites) (S) and is flanked by epidermal ectoderm (ECT). During neurulation, the neural plate buckles at its midline to form the neural folds and a floor plate (F) forms at its midline. The neural tube forms by fusion of the dorsal tips of the neural folds, generating roof plate cells at its dorsal midline and neural crest cells (NC), which emigrate from the dorsal neural tube. Neuroepithelial cells proliferate and differentiate into neurons located at different dorsoventral positions. Subclasses of commissural (C) and association (A) neurons differentiate dorsally, close to the roof plate, whereas motor neurons (M) and ventral interneurons (V) differentiate ventrally near the floor plate. Dorsal root ganglion (DRG) neurons are generated from post-migratory neural crest cells. (B) The diagram shows the source of ventralizing [Sonic Hedgehog (Shh), blue] and dorsalizing (BMPs, orange) inductive signals at sequential stages of spinal cord development. Shh is initially expressed in the axial mesoderm, and BMPs originate in the epidermal ectoderm flanking the lateral edges of the neural plate. At neural fold stages, Shh begins to be expressed by floor plate cells at the midline of the neural plate and BMPs by cells in the dorsal tips of the neural folds. After neural tube closure, BMP expression is lost from the epidermal ectoderm except at the dorsal midline but BMPs are now expressed in the roof plate and adjacent dorsal neural tube. At the onset of neuronal differentiation, BMP expression persists in the dorsal neural tube, and Shh expression is maintained in the floor plate.

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Science, Vol 274, Issue 5290, 1115-1123 , 15 November 1996 [HELP with high resolution image viewing] [Return to Article]
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