Changes in dorsoventral but not rostrocaudal regionalization of the chick neural tube in the absence of cranial notochord, as revealed by expression of Engrailed‐2

Abstract

Notochord has been implicated in previous studies in both the dorsoventral and rostrocaudal patterning of the developing neural tube. This possibility has been further explored by analyzing the expression of Engruiled-2 in chick embryos developing with cranial notochord defects. Control embryos containing intact notochords expressed Engruiled-2 protein within the neural tube and in a subset of the neural crest and overlying surface ectoderm at the future mesencephalon and cranial metencephalon levels. Within the neural tube, expression was confined to cell nuclei in the roof plate and lateral walls; floor plate nuclei directly overlying the notochord typically failed to show expression. After surgical removal of Hensen's node, the source of notochord precursor cells, embryos were cultured through neurulation and assayed for expression of Engrailed-2 protein. All embryos that partially or completely lacked cranial notochord expressed Engrailed-2 in a pattern similar to that of control embryos containing intact notochords, except that when notochord and floor plate were absent, Engrailed-2 was also expressed in the most ventral part of the neural tube. These results indicate that 1) Engruiled-2 expression is suppressed in the most ventral neural tube owing to induction of the floor plate by the notochord, and 2) that the presence of an underlying notochord is not required for correct rostrocaudal expression, suggesting that multiple pathways act in the patterning of the rudiment of the central nervous system. 0 1992 Wiley-Liss, Inc.

Positioning of the midbrain-hindbrain boundary organizer through global posteriorization of the neuroectoderm mediated by Wnt8 signaling

“…Work in several species suggests that signals from the anterior mesendoderm or notochord might regulate the expression of Engrailed genes in the neural plate (Hemmati-Brivanlou et al, 1990;Ang and Rossant, 1993;Darnell and Schoenwolf, 1997;Shamim et al, 1999). However, these findings are inconsistent with node removal experiments, which reveal correct AP patterning, including En2 expression, in the absence of axial mesendoderm (Darnell et al, 1992), and a role in refining rostrocaudal pattern has been suggested instead (Rowan et al, 1999;Camus et al, 2000). Moreover, in mouse or in zebrafish that lack the notochord, a well-formed neuraxis develops (Ang and Rossant, 1994;Weinstein et al, 1994;Klingensmith et al, 1999;Shih and Fraser, 1996;Saude et al, 2000).…”

Comparative study of shape, course, and disintegration of the rostral notochord in some vertebrates, especially humans

“…According to Darnell et al (1992), however, notochordless chick embryos have a normal overall pattern of chick En-2 protein expression. Furthermore, Gardner and Barald (1992) found Enprotein to appear in the "prechordal plate" and anterior notochord only some time after its expression in the mes-metencephalic neuroepithelium above.…”

Regulative ability of the prospective cardiogenic and vasculogenic areas of the primitive streak during avian gastrulation

“…Embryos for antiquail labeling were removed from cultures, fixed with 2% paraformaldehyde in 0.1 M phosphate buffer, washed with PBS, and then processed for whole-mount labeling as described by Darnell et al (1992). Briefly, embryos were treated with Triton X-100, to facilitate antibody penetration into tissues, and labeled overnight at 4°C with a 1:1,000 dilution of supernatant obtained from antiquail-secreting hybridoma cells.…”