Positive and negative signals modulate formation of the Xenopus cement gland

Development ◽  
1996 ◽  
Vol 122 (9) ◽  
pp. 2739-2750 ◽  
Author(s):  
L. Bradley ◽  
D. Wainstock ◽  
H. Sive
Keyword(s):  
Potent Inhibitor ◽  
Neural Plate ◽  
Cement Gland ◽  
Cell Interactions ◽  
Potent Inducer ◽  
Negative Cell ◽  
Complex Process ◽  
Dorsal Mesoderm ◽  
Dorsal Ectoderm ◽  
Early Gastrula

The cement gland is a simple secretory organ that marks the anterior-most dorsal ectoderm in Xenopus embryos. In this study, we examine the timing of cement gland induction and the cell interactions that contribute to cement gland formation. Firstly, we show that the outer ectodermal layer, from which the cement gland arises, becomes specified as cement gland by mid-gastrula. Curiously, at early gastrula, the inner layer of the dorsal ectoderm, which does not contribute to the mature cement gland, is strongly and transiently specified as cement gland. Secondly, we show that the mid-gastrula dorsoanterior yolky endoderm, which comes to underlie the cement gland primordium, is a potent inducer of cement gland formation and patterning. The cement gland itself has an anteroposterior pattern, with the gene XA expressed only posteriorly. Dorsoanterior yolky endoderm greatly enhances formation of large, patterned cement glands in partially induced anterodorsal ectoderm, but is unable to induce cement gland in naive animal caps. Neural tissue is induced less frequently than cement gland by the dorsoanterior yolky endoderm, suggesting that the endoderm induces cement gland directly. Thirdly, we demonstrate that the ventral ectoderm adjacent to the cement gland attenuates cement gland differentiation late during gastrulation. The more distant ventral mesendoderm is also a potent inhibitor of cement gland formation. These are the first data showing that normal ventral tissues can inhibit cement gland differentiation and suggest that cement gland size and position may be partly regulated by negative signals. Previous work has shown that cement gland can be induced by neural plate and by dorsal mesoderm. Together, these data suggest that cement gland induction is a complex process regulated by multiple positive and negative cell interactions.

XIPOU 2 is a potential regulator of Spemann's Organizer

Development ◽  
1997 ◽  
Vol 124 (6) ◽  
pp. 1179-1189 ◽  
Author(s):  
S.E. Witta ◽  
S.M. Sato
Keyword(s):  
Gene Expression ◽  
Wnt Pathway ◽  
Marginal Zone ◽  
Branchial Arch ◽  
Class Iii ◽  
Domain Family ◽  
Potent Inducer ◽  
Pou Domain ◽  
Spemann's Organizer ◽  
Dorsal Mesoderm

XIPOU 2, a member of the class III POU-domain family, is expressed initially at mid-blastula transition (MBT) and during gastrulation in the entire marginal zone mesoderm, including Spemann's Organizer (the Organizer). To identify potential targets of XIPOU 2, the interaction of XIPOU 2 with other genes co-expressed in the Organizer was examined by microinjecting XIPOU 2's mRNA into the lineage of cells that contributes to the Organizer, head mesenchyme and prechordal plate. XIPOU 2 suppresses the expression of a number of dorsal mesoderm-specific genes, including gsc, Xlim-1, Xotx2, noggin and chordin, but not Xnot. As a consequence of the suppression of dorsal mesoderm gene expression, bone morphogenetic factor-4 (Bmp-4), a potent inducer of ventral mesoderm, is activated in the Organizer. Gsc is a potential target of XIPOU 2. XIPOU 2 is capable of binding a class III POU protein binding site (CATTAAT) that is located within the gsc promoter, in the activin-inducible (distal) element. Furthermore, XIPOU 2 suppresses the activation of the gsc promoter by activin signaling. At the neurula and tailbud stages, dorsoanterior structures are affected: embryos displayed micropthalmia and the loss of the first branchial arch, as detected by the expression of pax-6, Xotx2 and en-2. By examining events downstream from the Wnt and chordin pathways, we determined that XIPOU 2, when overexpressed, acts specifically in the Organizer, downstream from GSK-3beta of the Wnt pathway and upstream from chordin. The interference in dorsalizing events caused by XIPOU 2 was rescued by chordin. Thus, in addition to its direct neuralizing ability, in a different context, XIPOU 2 has the potential to antagonize dorsalizing events in the Organizer.

A study of the properties, morphogenetic potencies and prospective fate of outer and inner layers of ectodermal and chordamesodermal regions during gastrulation, in various Anuran amphibians

Development ◽  
1983 ◽  
Vol 75 (1) ◽  
pp. 67-86
Author(s):  
T. A. Dettlaff
Keyword(s):  
Outer Layer ◽  
Normal Development ◽  
Neural Plate ◽  
Ependymal Cells ◽  
Epithelial Layer ◽  
Bombina Bombina ◽  
Cell Layers ◽  
The Brain ◽  
Early Gastrula

In both the ectodermal and the chordamesodermal regions of Anuran embryos, the outer layer of cells possesses epithelial properties and has the same restricted morphogenetic potencies. It is thus interchangeable between the regions, capable of epiboly and, when underlain by notochord material, of the formation of bottle-shaped cells as at the blastoporal groove, and invagination. When taken from the chordamesoderm region, this outer layer has no inducing effect on the ectoderm of the early gastrula. In normal development the outer layer of the neural plate takes an active part in forming the neural tube cavity. It gives rise to the neuroepithelial roof of the diencephalon and medulla oblongata and, when underlain by neuroblasts that develop from the inner cell layers, to ependymal cells of the brain wall. The outer layer of the notochord material is included in the epithelial layer underlying the roof of the gastrocoel - the hypochordal plate. The inner layers of these regions consist of loosely arranged cells and normally have no epithelial properties although, when taken from the ectoderm region, they may acquire such properties upon long-term contact with the environment. However they have wide morphogenetic potencies; the differences in these potencies between cells taken from the various presumptive regions being less than the differences between outer and inner cell layers in each region. Maps are provided which show the arrangement of presumptive rudiments in the ectoderm and chordamesoderm on sagittal sections through Bombina bombina embryos in early and late gastrulation.

Geminin, a neuralizing molecule that demarcates the future neural plate at the onset of gastrulation

Development ◽  
1998 ◽  
Vol 125 (16) ◽  
pp. 3247-3258 ◽  
Author(s):  
K.L. Kroll ◽  
A.N. Salic ◽  
L.M. Evans ◽  
M.W. Kirschner
Keyword(s):  
Cell Fate ◽  
Sequence Similarity ◽  
Coiled Coil ◽  
Gene Families ◽  
Neural Plate ◽  
Dominant Negative ◽  
Expression Cloning ◽  
Bmp4 Expression ◽  
Neural Cell Fate ◽  
Early Gastrula

In an expression cloning screen in Xenopus embryos, we identified a gene that when overexpressed expanded the neural plate at the expense of adjacent neural crest and epidermis. This gene, which we named geminin, had no sequence similarity to known gene families. We later discovered that geminin's neuralizing domain was part of a bifunctional protein whose C-terminal coiled-coil domain may play a role in regulating DNA replication. We report here on the neuralizing function of geminin. The localization, effect of misexpression and activity of a dominant negative geminin suggest that the product of this gene has an essential early role in specifying neural cell fate in vertebrates. Maternal geminin mRNA is found throughout the animal hemisphere from oocyte through late blastula. At the early gastrula, however, expression is restricted to a dorsal ectodermal territory that prefigures the neural plate. Misexpression of geminin in gastrula ectoderm suppresses BMP4 expression and converts prospective epidermis into neural tissue. In ectodermal explants, geminin induces expression of the early proneural gene neurogenin-related 1 although not itself being induced by that gene. Later, embryos expressing geminin have an expanded dorsal neural territory and ventral ectoderm is converted to neurons. A putative dominant negative geminin lacking the neuralizing domain suppresses neural differentiation and, when misexpressed dorsally, produces islands of epidermal gene expression within the neurectodermal territory, effects that are rescued by coexpression of the full-length molecule. Taken together, these data indicate that geminin plays an early role in establishing a neural domain during gastrulation.

scholarly journals The patterning and functioning of protrusive activity during convergence and extension of the Xenopus organiser

Development ◽  
1992 ◽  
Vol 116 (Supplement) ◽  
pp. 81-91 ◽  
Author(s):  
Ray Keller ◽  
John Shih ◽  
Carmen Domingo
Keyword(s):  
Spinal Cord ◽  
Nervous System ◽  
Marginal Zone ◽  
Tissue Differentiation ◽  
Tissue Interactions ◽  
Dorsal Mesoderm ◽  
Convergence And Extension ◽  
Early Gastrula ◽  
Ventral Explants ◽  
Anterior Posterior

We discuss the cellular basis and tissue interactions regulating convergence and extension of the vertebrate body axis in early embryogenesls of Xenopus. Convergence and extension occur in the dorsal mesoderm (prospective notochord and somite) and in the posterior nervous system (prospective hindbrain and spinal cord) by sequential cell intercalations. Several layers of cells intercalate to form a thinner, longer array (radial intercalation) and then cells intercalate in the mediolateral orientation to form a longer, narrower array (mediolateral intercalation). Fluorescence microscopy of labeled mesodermal cells in explants shows that protrusive activity is rapid and randomly directed until the midgastrula stage, when it slows and is restricted to the medial and lateral ends of the cells. This bipolar protrusive activity results in elongation, alignment and mediolateral intercalation of the cells. Mediolateral intercalation behavior (MIB) is expressed in an anterior-posterior and lateral-medial progression in the mesoderm. MIB is first expressed laterally in both somitic and notochordal mesoderm. From its lateral origins in each tissue, MIB progresses medially. If convergence does not bring the lateral boundaries of the tissues closer to the medial cells in the notochordal and somitic territories, these cells do not express MIB. Expression of tissue-specific markers follows and parallels the expression of MIB. These facts argue that MIB and some aspects of tissue differentiation are induced by signals emanating from the lateral boundaries of the tissue territories and that convergence must bring medial cells and boundaries closer together for these signals to be effective. Grafts of dorsal marginal zone epithelium to the ventral sides of other embryos, to ventral explants and to UV-ventralized embryos show that it has a role in organising convergence and extension, and dorsal tissue differentiation among deep mesodermal cells. Grafts of involuting marginal zone to animal cap tissue of the early gastrula shows that convergence and extension of the hindbrain-spinal cord are induced by planar signals from the involuting marginal zone.

Fibroblast growth factor is a direct neural inducer, which combined with noggin generates anterior-posterior neural pattern

Development ◽  
1995 ◽  
Vol 121 (11) ◽  
pp. 3627-3636 ◽  
Author(s):  
T.M. Lamb ◽  
R.M. Harland
Keyword(s):  
Neural Induction ◽  
Neural Tissue ◽  
Mesoderm Induction ◽  
Gastrula Stage ◽  
Neural Patterning ◽  
The Third ◽  
Dorsal Mesoderm ◽  
Early Gastrula ◽  
Anterior Posterior ◽  
Mesodermal Tissue

Neural tissue in developing Xenopus embryos is induced by signals from the dorsal mesoderm. Induction of anterior neural tissue could be mediated by noggin, a secreted polypeptide found in dorsal mesoderm. We show that bFGF, a known mesoderm inducer of blastula staged ectoderm, induces neural tissue from gastrula stage ectoderm. The type of neural tissue induced by bFGF from stage 10.25 ectoderm is posterior, as marked by Hox B9 expression. When bFGF and noggin are combined on early gastrula stage ectoderm, a more complete neural pattern is generated and no mesodermal tissue is detected. Explants treated with noggin and bFGF elongate and display distinct anterior and posterior ends marked by otx2 and Hox B9 expression, respectively. Furthermore, treatment of early gastrula ectoderm with noggin and bFGF results in the induction of En-2, a marker of the midbrain-hindbrain junction and Krox 20, a marker of the third and fifth rhombomeres of the hindbrain. Neither of these genes is induced by noggin alone or bFGF alone at this stage, suggesting a synergy in anterior-posterior neural patterning. The response of later gastrula (stage 11–12) ectoderm to bFGF changes so that Krox 20 and En-2 are induced by bFGF alone, while induction of more posterior tissue marked by Hox B9 is eliminated. The dose of bFGF affects the amount of neural tissue induced, but has little effect on the anterior-posterior character, rather the age of the ectoderm treated is the determinant of the response. Thus, an FGF signal may account for posterior neural induction, and anterior-posterior neural patterning could be partly explained by the actions of noggin and FGF, together with the changing response of the ectoderm to these factors.

Differential gene expression in the anterior neural plate during gastrulation of Xenopus laevis

Development ◽  
1989 ◽  
Vol 105 (4) ◽  
pp. 779-786 ◽  
Author(s):  
M. Jamrich ◽  
S. Sato
Keyword(s):  
Gene Expression ◽  
Xenopus Laevis ◽  
Neural Induction ◽  
Neural Plate ◽  
Cement Gland ◽  
Cdna Clones ◽  
Differential Gene ◽  
Anteroposterior Polarity ◽  
Xenopus Laevis Embryos ◽  
Anterior Neural Plate

We have isolated three cDNA clones that are preferentially expressed in the cement gland of early Xenopus laevis embryos. These clones were used to study processes involved in the induction of this secretory organ. Results obtained show that the induction of this gland coincides with the process of neural induction. Genes specific for the cement gland are expressed very early in the anterior neural plate of stage-12 embryos. This suggests that the anteroposterior polarity of the neural plate is already established during gastrulation. At later stages of development, two of the three genes have secondary sites of expression. The expression of these genes can be induced in isolated animal caps by incubation in 10 mM-NH4Cl, a treatment that is known to induce cement glands.

scholarly journals XASH genes promote neurogenesis in Xenopus embryos

Development ◽  
1994 ◽  
Vol 120 (12) ◽  
pp. 3649-3655 ◽  
Author(s):  
B. Ferreiro ◽  
C. Kintner ◽  
K. Zimmerman ◽  
D. Anderson ◽  
W.A. Harris
Keyword(s):  
Neural Development ◽  
Neural Induction ◽  
Neural Tissue ◽  
Neural Plate ◽  
Binding Partner ◽  
Helix Loop Helix ◽  
Neural Genes ◽  
Dorsal Ectoderm ◽  
Bhlh Transcription Factors ◽  
Beta Tubulin Gene

Neural development in Drosophila is promoted by a family of basic helix-loop-helix (bHLH) transcription factors encoded within the Achaete Scute-Complex (AS-C). XASH-3, a Xenopus homolog of the Drosophila AS-C genes, is expressed during neural induction within a portion of the dorsal ectoderm that gives rise to the neural plate and tube. Here, we show that XASH-3, when expressed with the promiscuous binding partner XE12, specifically activates the expression of neural genes in naive ectoderm, suggesting that XASH-3 promotes neural development. Moreover, XASH-3/XE12 RNA injections into embryos lead to hypertrophy of the neural tube. Interestingly, XASH-3 misexpression does not lead to the formation of ectopic neural tissue in ventral regions, suggesting that the domain of XASH proneural function is restricted in the embryo. In contrast to the neural inducer noggin, which permanently activates the NCAM gene, the activation of neural genes by XASH-3/XE12 is not stable in naive ectoderm, yet XASH-3/XE12 powerfully and stably activates NCAM, Neurofilament and type III beta-tubulin gene expression in noggin-treated ectoderm. These results show that the XASH-3 promotes neural development, and suggest that its activity depends on additional factors which are induced in ectoderm by factors such as noggin.

The homeobox gene Siamois is a target of the Wnt dorsalisation pathway and triggers organiser activity in the absence of mesoderm

Development ◽  
1996 ◽  
Vol 122 (10) ◽  
pp. 3055-3065 ◽  
Author(s):  
G. Carnac ◽  
L. Kodjabachian ◽  
J.B. Gurdon ◽  
P. Lemaire
Keyword(s):  
Gene Expression ◽  
Target Genes ◽  
Homeobox Gene ◽  
Neural Tissue ◽  
Wnt Signalling ◽  
Cement Gland ◽  
Signalling Pathway ◽  
Mesoderm Induction ◽  
Embryonic Cells ◽  
Dorsal Mesoderm

Siamois, a Xenopus zygotic homeobox gene with strong dorsalising activity, is expressed in the dorsal-vegetal organiser known as the Nieuwkoop centre. We show that, in contrast to Spemann organiser genes such as goosecoid, chordin and noggin, Siamois gene expression is not induced following overexpression of mesoderm inducers in ectodermal (animal cap) cells. However, Siamois is induced by overexpressing a dorsalising Wnt molecule. Furthermore, like Wnt, Siamois can dorsalise ventral mesoderm and cooperate with Xbrachyury to generate dorsal mesoderm. These results suggest that Siamois is a mediator of the Wnt-signalling pathway and that the synergy between the Wnt and mesoderm induction pathways occurs downstream of the early target genes of these two pathways. Overexpression of Siamois in animal cap cells reveals that this gene can act in a non vegetal or mesodermal context. We show the following. (1) Animal cap cells overexpressing Siamois secrete a factor able to dorsalise ventral gastrula mesoderm in tissue combination experiments. (2) The Spemann organiser-specific genes goosecoid, Xnr-3 and chordin, but not Xlim.1, are activated in these caps while the ventralising gene Bmp-4 is repressed. However, the dorsalising activity of Siamois-expressing animal caps is significantly different from that of noggin- or chordin-expressing animal caps, suggesting the existence of other dorsalising signals in the embryo. (3) Ectodermal cells overexpressing Siamois secrete a neuralising signal and can differentiate into cement gland and, to a lesser extent, into neural tissue. Hence, in the absence of mesoderm induction, overexpression of Siamois is sufficient to confer organiser properties on embryonic cells.

Timing and cell interactions underlying neural induction in the chick embryo

Development ◽  
1999 ◽  
Vol 126 (11) ◽  
pp. 2505-2514
Author(s):  
D.K. Darnell ◽  
M.R. Stark ◽  
G.C. Schoenwolf
Keyword(s):  
Neural Induction ◽  
Primitive Streak ◽  
Model System ◽  
Neural Plate ◽  
Neural Specification ◽  
Organizer Activity ◽  
Plate Morphology ◽  
Improved Model ◽  
Differentiation Event ◽  
Early Gastrula

Previous studies on neural induction have identified regionally localized inducing activities, signaling molecules, potential competence factors and various other features of this important, early differentiation event. In this paper, we have developed an improved model system for analyzing neural induction and patterning using transverse blastoderm isolates obtained from gastrulating chick embryos. We use this model to establish the timing of neural specification and the spatial distribution of perinodal cells having organizer activity. We show that a tissue that acts either as an organizer or as an inducer of an organizer is spatially co-localized with the prospective neuroectoderm immediately rostral to the primitive streak in the early gastrula. As the primitive streak elongates, this tissue with organizing activity and the prospective neuroectoderm rostral to the streak separate. Furthermore, we show that up to and through the mid-primitive streak stage (i.e., stage 3c/3+), the prospective neuroectoderm cannot self-differentiate (i.e., express neural markers and acquire neural plate morphology) in isolation from tissue with organizer activity. Signals from the organizer and from other more caudal regions of the primitive streak act on the rostral prospective neuroectoderm and the latter gains potency (i.e., is specified) by the fully elongated primitive streak stage (i.e., stage 3d). Transverse blastoderm isolates containing non-specified, prospective neuroectoderm provide an improved model system for analyzing early signaling events involved in neuraxis initiation and patterning.

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