Grunz H et al. (1995), The role of vertical and planar signals during ...

XB-ART-19678

Int J Dev Biol 1995 Jun 01;393:539-43.

Show Gene links Show Anatomy links

The role of vertical and planar signals during the early steps of neural induction.

Grunz H , Schüren C , Richter K .

???displayArticle.abstract???
The classical Einsteck-test (Spemann and Mangold, Roux Arch. Dev. Biol. 100: 599-638, 1924) and data from total exogastrulae (Holtfreter, 1933) suggest that vertical signals are transmitted between the chordamesoderm (organizer) and reacting ectoderm in the early phase of neural induction. In contrast to these results with Axoloti (urodeles), several authors observed the expression of neural specific genes in Xenopus exogastrulae, isolated dorsal blastopore lip with adjacent ectoderm (open-face explants) and Keller-sandwiches. Our data with Xenopus (anurans) also show that the expression of neural specific genes takes place in exogastrulae. However, when we prepared open face explants and exogastrula-like structures by microdissection at very early gastrula stage, the signal of a class II beta-tubulin, characteristic of terminal neural differentiation, is not found in the ectoderm. These results suggest that planar signals transmitted from the chordamesoderm into the ectodermal part can fairly be excluded under these experimental conditions. In similar experiments with Triturus alpestris we could not observe either the differentiation of neural structures in the ectodermal part of exogastrulae. These results confirm earlier experiments of Holtfreter performed with Ambystoma mexicanum (Axoltl) embryos. On the basis of the published data of different authors and our results, we cannot exclude the existence of planar signals for early and/or transient expressed genes before the onset of gastrulation in Xenopus, which make the neuroectoderm susceptible for the response to vertical signals during gastrulation. On the other hand our experiments with Triturus alpestris suggest that planar neural signals are unlikely in this species. These differences between Triturus and Xenopus embryos are discussed in the context of the peculiarities in morphological structure, competence and speed of development of the two species.

???displayArticle.pubmedLink??? 7577445
???displayArticle.link??? Int J Dev Biol

Species referenced: Xenopus laevis
Genes referenced: tubb2b

???attribute.lit??? ???displayArticles.show???

Fig. 3. Neural signals and differentiation in exogastrulae and open-face explants. (A) Pseudoexogastrulae (Xenopus) prepared by microdissection described in Fig. 1. After 24 h the exogastrulae were fixed for whole-mount in situ hybridization with a neural specific f3-tubulin. The signal (neural specific tubulin) is seen only in the intermediate zone between the ectoderm and the endomesoderm farrows). (B) Open-face explant without the superficial/ayer prepared by the technique described in Fig 2. The signal of the neural-specific beta-tubulins seen in the intermediate zone between chordamesoderm and ectoderm (ee) only (arrows). (C) Open-face explant with superficial and inner layers prepared by the technique described in Fig. 2. The signal of the neural specific r3-tubulin is expressed in the intermediate zone between chordamesoderm and ectoderm (ec) only (arrow). The other explant on the left side also shows faint staining in the middle part of the ectoderm (arrowhead). (D) Histological section of an open-face explant contains a few neural cells (neu) in the vicinity of notochord (no) only. ce, cement gland in the ectodermal part of the explant. The blue color in this micrograph represents anilin-blue (normal histology), which has stained the mucous material of the cement gland. tEl A selection of pseudoexogastrulae (Triturus alpestris) prepared by microdissection descnbed under Fig. 1. After 10 days culture at 2OoC the ectoderm has separated from the endomesoderm (end) and has differentiated into atypical (ciliated) epidermis (ec). IF) Histological section of the explant of panel E (arrow) shows that archencephalic brain structures (eye with lens, arrow) have differentiated in the intermediate zone between atypical epldermls(ec) and the endomesodermal area only. Most of the ectodermal parr (only one third is shown) has differentiated into atypical epidermis (ciliated) epidermis only. notochord (no), somites(so).