Patterning the Vertebrate Neuraxis

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Science  15 Nov 1996:
Vol. 274, Issue 5290, pp. 1109-1115
DOI: 10.1126/science.274.5290.1109


  • Fig. 1.

    Acquisition of AP pattern during neural induction in Xenopus. In the late gastrula, shown in hemisection, involuted cells have reached the anterior pole of the presumptive CNS. Radial signals (white arrows) from the leading-edge endoderm (yellow) and the mesoderm (orange) induce neural fate in the overlying ectoderm (blue). Forebrain (dark pink) is induced by leading-edge endoderm and mesoderm. More posterior levels of the ectoderm are activated (light pink) and transformed by a graded posteriorizing activity (green). The yellow arrow shows the route of planar signals.

  • Fig. 2.

    Patterns of cell organization in the 3-day embryonic chick hindbrain. Superimposed on the rhombomere pattern (r1 to r7) are the reticular neurons (left side) and the motor neurons (right side). Reticular neurons are classified (and colored blue or green) according to axonal trajectory. Motor neurons (in the right side basal plate, B) are classified as somatomotor (yellow), innervating extrinsic eye muscles (IV, troclear; VI, abducens); branchiomotor (orange), innervating branchial muscles in the first arch (V, trigeminal), second arch (VII, facial), and third arch (IX, glossopharyngeal); and vestibuloacoustic efferents (red), which share the VIIth nerve exit point (dotted circle) with the facial motor neurons in the alar plate (A). F, floor plate.

  • Fig. 3.

    Stages leading to cell compartmentation and rhombomere boundary (yellow) formation in the chick embryo. An adhesion differential between adjacent domains (blue, green) segregates cells at the interfaces. Although the molecular basis of the differential adhesion is unknown, it follows the same two-segment repeat as displayed by Krox-20 and other genes shown in Fig. 4. Molecules with boundary-restricted expression (yellow) include Plzf (39), Fgf-3 (40), vimentin (38), low-PSA-NCAM, and laminin (23). Stages numbers refer to normal chick development.

  • Fig. 4.

    Summary of the correlation of gene expression with specific rhombomeres, compiled from analysis in mouse and chick embryos. (Top) Odd-numbered rhombomeres are indicated in blue and even-numbered rhombomeres in green, with each segment designated as r1 to r7. The rod-like notochord and overlying floorplate are indicated in black. The vertical yellow lines indicate the boundaries between rhombomeres. The patterns of gene expression are depicted in arbitrary colors with the darkest colors indicating the highest levels of expression. Related genes are indicated by the same color for convenience: Hox homeobox genes (orange), Eph family tyrosine kinase receptors (blue), Eph receptor ligands (green), retinoid- or signaling-related genes (magenta), and early expressed transcription factors (dark purple).

  • Fig. 5.

    Early midbrain patterning. In an early neural tube stage embryo, Fgf-8 (green) is expressed in a ring of cells at the isthmus, the constriction between the mesencephalic vesicle (M), and rhombomere 1 (r1). Wnt-1 (yellow) is expressed in a ring of cells immediately rostral to Fgf-8 and along the dorsal midline. Both En-1 and En-2 (blue) are expressed in gradients that decrease anteriorly and posteriorly from the isthmus. Sonic hedgehog (Shh) expression, at the ventral midline, is shown in red. T, telencephalon; D, diencephalon; SC, spinal cord; N, notochord.