Analysis of Xwnt-4 in embryos of Xenopus laevis: a Wnt family member expressed in the brain and floor plate

This study characterizes the temporal and spatial expression during early Xenopus development of Xwnt-4, a member of the Wnt gene family. The Xwnt-4 protein contains all of the sequence motifs that are hallmarks of the Wnt gene family and is 84% identical to the mouse homolog, Wnt-4. The highest level of Xwnt-4 expression occurs during the early neurula stage of development although its expression persists throughout embryogenesis and can be found in the adult testis, brain and epithelium. Consistent with its localization to head and dorsal regions of microdissected embryos, the expression of Xwnt-4 is enhanced in anterodorsalized embryos resulting from treatment with LiCl, and the expression of Xwnt-4 is suppressed in UV-ventralized embryos that lack anterior neural tissue. These results suggested that expression of Xwnt-4 is dependent on the induction of neural tissue. This idea was tested using induction experiments with dorsal or ventral ectoderm from a stage 10 embryo, recombined with dorsal marginal zone mesoderm from the same embryo. Recombinant tissue and ectoderm alone were cultured until stage 14, when Xwnt-4 expression was assayed using Northern analysis. In the recombinant assay, Xwnt-4 expression does not occur in the uninduced ectoderm but is expressed in both the dorsal and ventral recombinants. Xwnt-4 expression in neural ectoderm was confirmed in isolated, induced neural ectoderm, dissected away from the dorsal mesoderm, in a stage 12.5 embryo. Whole-mount in situ hybridization confirmed the dissection studies and demonstrated that Xwnt-4 transcripts are expressed in the dorsal midline of the midbrain, hindbrain and the floor plate of the neural tube. Collectively, the data indicate that Xwnt-4 is a unique member of the Wnt family whose expression is dependent on neural induction. The specific pattern of expression following neural induction suggests that Xwnt-4 plays a role in the early patterning events responsible in the formation of the nervous system in Xenopus.

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Patterning of the neural ectoderm of Xenopus laevis by the amino-terminal product of hedgehog autoproteolytic cleavage

Development ◽

10.1242/dev.121.8.2349 ◽

1995 ◽

Vol 121 (8) ◽

pp. 2349-2360 ◽

Cited By ~ 12

Author(s):

C.J. Lai ◽

S.C. Ekker ◽

P.A. Beachy ◽

R.T. Moon

Keyword(s):

Gene Family ◽

Neural Induction ◽

Neural Tissue ◽

Internal Deletion ◽

Anteroposterior Patterning ◽

Amino Terminal ◽

Neural Genes ◽

Neural Ectoderm ◽

Amino Terminal Domain ◽

Autoproteolytic Cleavage

The patterns of embryonic expression and the activities of Xenopus members of the hedgehog gene family are suggestive of role in neural induction and patterning. We report that these hedgehog polypeptides undergo autoproteolytic cleavage. Injection into embryos of mRNAs encoding Xenopus banded-hedgehog (X-bhh) or the amino-terminal domain (N) demonstrates that the direct inductive activities of X-bhh are encoded by N. In addition, both N and X-bhh pattern neural tissue by elevating expression of anterior neural genes. Unexpectedly, an internal deletion of X-bhh (delta N-C) was found to block the activity of X-bhh and N in explants and to reduce dorsoanterior structures in embryos. As elevated hedgehog activity increases the expression of anterior neural genes, and as delta N-C reduces dorsoanterior structures, these complementary data support a role for hedgehog in neural induction and anteroposterior patterning.

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Establishing embryonic territories in the context of Wnt signaling

The International Journal of Developmental Biology ◽

10.1387/ijdb.200231ja ◽

2020 ◽

Vol 52 ◽

Author(s):

Ian Velloso ◽

Lorena A. Maia ◽

Nathalia G. Amado ◽

Alice H. Reis ◽

Xi He ◽

...

Keyword(s):

Wnt Pathway ◽

Neural Induction ◽

Neural Tissue ◽

Research Groups ◽

Major Player ◽

History Of ◽

Neural Ectoderm ◽

Trunk Organizer ◽

Early Gastrula ◽

Developmental Windows

This review highlights the work that my research group has been developing, together with international collaborators, during the last decade. Since we were able to establish Xenopus laevis experimental model in Brazil we have been focused on understanding early embryonic patterns regarding neural induction and axes establishment. In this context, Wnt pathway appears as a major player and has been much explored by us and other research groups. Here we chose to review three published works that we consider landmarks within the history of our research on the developmental biology field and the neural induction and patterning modern findings. We intend to show how our series of discoveries, when painted together, tells a story that covers crucial developmental windows of early differentiation paths of anterior neural tissue. Being those: 1. Establishing Head organizer in contrast to trunk organizer at early gastrula; 2. deciding between neural ectoderm and epidermis ectoderm at the blastula/gastrula stages, and 3. the gathering of prechordal unique properties at late gastrula/early neurula.

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Schizosaccharomyces pombe ras1 and byr1 are functionally related genes of the ste family that affect starvation-induced transcription of mating-type genes.

Molecular and Cellular Biology ◽

10.1128/mcb.10.2.549 ◽

1990 ◽

Vol 10 (2) ◽

pp. 549-560 ◽

Cited By ~ 43

Author(s):

S A Nadin-Davis ◽

A Nasim

Keyword(s):

Gene Family ◽

Fission Yeast ◽

Mating Type ◽

Growth Cycle ◽

Yeast Cells ◽

Null Alleles ◽

Northern Analysis ◽

Gene Transcript ◽

Type Gene

We have further investigated the function of the ras1 and byr1 genes, which were previously shown to be critical for sexual differentiation in fission yeast cells. Several physiological similarities between strains containing null alleles of these genes supports the idea that ras1 and byr1 are functionally closely related. Furthermore, we have found that byr1 is allelic to ste1, one of at least 10 genes which when mutated can cause sterility. Since ras1 had previously been found to be allelic to ste5, both ras and byr genes are now clearly shown to be a part of the ste gene family, thus confirming their close functional relationship. The observation that the mating-type loci could overcome the sporulation block of ras1 and byr1 mutant strains prompted investigation of the role of the ras-byr pathway in the induction of the mating-type gene transcripts upon nitrogen starvation. By Northern analysis of RNA preparations from strains carrying wild-type or mutant ras1 alleles and grown to different stages of the growth cycle, we have shown that ras1 plays an important role in inducing the Pi transcript of the mating-type loci and the mei3 gene transcript. These observations provide a molecular basis for the role of the ste gene family, including ras1 and byr1, in meiosis and indicate that further characterization of other ste genes would be very useful for elucidating the mechanism of ras1 function in fission yeast cells.

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Spatial aspects of neural induction in Xenopus laevis

Development ◽

10.1242/dev.107.4.785 ◽

1989 ◽

Vol 107 (4) ◽

pp. 785-791 ◽

Cited By ~ 10

Author(s):

E.A. Jones ◽

H.R. Woodland

Keyword(s):

Central Nervous System ◽

Nervous System ◽

Peripheral Nerves ◽

Neural Differentiation ◽

Neural Induction ◽

Neural Tissue ◽

Thoracic Region ◽

Lateral Extent ◽

Tail Tip ◽

Developing Nervous System

A monoclonal antibody, 2G9, has been identified and characterised as a marker of neural differentiation in Xenopus. The epitope is present throughout the adult central nervous system and in peripheral nerves. Staining is first detected in embryos at stage 21 in the thoracic region. By stage 29 it stains the whole central nervous system, except the tail tip. The epitope is present in a 65K Mr protein, and includes sialic acid. The antibody also reacts with neural tissue in mice and axolotls and newts. 2G9 was used to show that both notochord and somites are capable of neural induction, and the stimulus is present as late as stage 22. Attempts to demonstrate the induction of nervous system by developing nervous system (homoiogenetic induction) were unsuccessful. The view that the lateral extent of the nervous system might be determined by that of the inductive stimulus is discussed. Neural induction was detected as early as stage 10 and occurs in embryos without gastrulation and without cell division from stage 7 1/2.

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Early posterior neural tissue is induced by FGF in the chick embryo

Development ◽

10.1242/dev.125.3.473 ◽

1998 ◽

Vol 125 (3) ◽

pp. 473-484 ◽

Cited By ~ 14

Author(s):

K.G. Storey ◽

A. Goriely ◽

C.M. Sargent ◽

J.M. Brown ◽

H.D. Burns ◽

...

Keyword(s):

Chick Embryo ◽

Cell Fate ◽

Neural Induction ◽

Neural Tissue ◽

Primitive Streak ◽

Specific Aspect ◽

Amphibian Embryo ◽

Fgf Signalling ◽

Unique Cell ◽

Neural Cell Fate

Signals that induce neural cell fate in amniote embryos emanate from a unique cell population found at the anterior end of the primitive streak. Cells in this region express a number of fibroblast growth factors (FGFs), a group of secreted proteins implicated in the induction and patterning of neural tissue in the amphibian embryo. Here we exploit the large size and accessibility of the early chick embryo to analyse the function of FGF signalling specifically during neural induction. Our results demonstrate that extraembryonic epiblast cells previously shown to be responsive to endogenous neural-inducing signals express early posterior neural genes in response to local, physiological levels of FGF signal. This neural tissue does not express anterior neural markers or undergo neuronal differentiation and forms in the absence of axial mesoderm. Prospective mesodermal tissue is, however, induced and we present evidence for both the direct and indirect action of FGFs on prospective posterior neural tissue. These findings suggest that FGF signalling underlies a specific aspect of neural induction, the initiation of the programme that leads to the generation of the posterior central nervous system.

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Schizosaccharomyces pombe ras1 and byr1 are functionally related genes of the ste family that affect starvation-induced transcription of mating-type genes

Molecular and Cellular Biology ◽

10.1128/mcb.10.2.549-560.1990 ◽

1990 ◽

Vol 10 (2) ◽

pp. 549-560

Author(s):

S A Nadin-Davis ◽

A Nasim

Keyword(s):

Gene Family ◽

Fission Yeast ◽

Mating Type ◽

Growth Cycle ◽

Yeast Cells ◽

Null Alleles ◽

Northern Analysis ◽

Gene Transcript ◽

Type Gene

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Dual origin of the floor plate in the avian embryo

Development ◽

10.1242/dev.129.20.4785 ◽

2002 ◽

Vol 129 (20) ◽

pp. 4785-4796 ◽

Cited By ~ 6

Author(s):

Jean-Baptiste Charrier ◽

Françoise Lapointe ◽

Nicole M. Le Douarin ◽

Marie-Aimée Teillet

Keyword(s):

Time Window ◽

Gene Expression Pattern ◽

Floor Plate ◽

Avian Embryo ◽

Plate Formation ◽

Unknown Factor ◽

Short Time Window ◽

Neural Ectoderm ◽

Dual Origin ◽

Short Time

Molecular analysis carried out on quail-chick chimeras, in which quail Hensen’s node was substituted for its chick counterpart at the five- to six-somite stage (ss), showed that the floor plate of the avian neural tube is composed of distinct areas: (1) a median one (medial floor plate or MFP) derived from Hensen’s node and characterised by the same gene expression pattern as the node cells (i.e. expression of HNF3β and Shh to the exclusion of genes early expressed in the neural ectoderm such as CSox1); and (2) lateral regions that are differentiated from the neuralised ectoderm (CSox1 positive) and form the lateral floor plate (LFP). LFP cells are induced by the MFP to express HNF3β transiently, Shh continuously and other floor-plate characteristic genes such as Netrin. In contrast to MFP cells, LFP cells also express neural markers such as Nkx2.2 and Sim1. This pattern of avian floor-plate development presents some similarities to floor-plate formation in zebrafish embryos. We also demonstrate that, although MFP and LFP have different embryonic origins in normal development, one can experimentally obtain a complete floor plate in the neural epithelium by the inductive action of either a notochord or a MFP. The competence of the neuroepithelium to respond to notochord or MFP signals is restricted to a short time window, as only the posterior-most region of the neural plate of embryos younger than 15 ss is able to differentiate a complete floor plate comprising MFP and LFP. Moreover, MFP differentiation requires between 4 and 5 days of exposure to the inducing tissues. Under the same conditions LFP and SHH-producing cells only induce LFP-type cells. These results show that the capacity to induce a complete floor plate is restricted to node-derived tissues and probably involves a still unknown factor that is not SHH, the latter being able to induce only LFP characteristics in neuralised epithelium.

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Chordin regulates primitive streak development and the stability of induced neural cells, but is not sufficient for neural induction in the chick embryo

Development ◽

10.1242/dev.125.3.507 ◽

1998 ◽

Vol 125 (3) ◽

pp. 507-519 ◽

Cited By ~ 14

Author(s):

A. Streit ◽

K.J. Lee ◽

I. Woo ◽

C. Roberts ◽

T.M. Jessell ◽

...

Keyword(s):

Neural Induction ◽

Neural Tissue ◽

Primitive Streak ◽

Neural Plate ◽

Neural Cells ◽

Morphogenetic Protein ◽

Neural Markers ◽

Bmp Signalling ◽

The Stability ◽

Area Pellucida

We have investigated the role of Bone Morphogenetic Protein 4 (BMP-4) and a BMP antagonist, chordin, in primitive streak formation and neural induction in amniote embryos. We show that both BMP-4 and chordin are expressed before primitive streak formation, and that BMP-4 expression is downregulated as the streak starts to form. When BMP-4 is misexpressed in the posterior area pellucida, primitive streak formation is inhibited. Misexpression of BMP-4 also arrests further development of Hensen's node and axial structures. In contrast, misexpression of chordin in the anterior area pellucida generates an ectopic primitive streak that expresses mesoderm and organizer markers. We also provide evidence that chordin is not sufficient to induce neural tissue in the chick. Misexpression of chordin in regions outside the future neural plate does not induce the early neural markers L5, Sox-3 or Sox-2. Furthermore, neither BMP-4 nor BMP-7 interfere with neural induction when misexpressed in the presumptive neural plate before or after primitive streak formation. However, chordin can stabilise the expression of early neural markers in cells that have already received neural inducing signals. These results suggest that the regulation of BMP signalling by chordin plays a role in primitive streak formation and that chordin is not sufficient to induce neural tissue.

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

Development ◽

10.1242/dev.121.11.3627 ◽

1995 ◽

Vol 121 (11) ◽

pp. 3627-3636 ◽

Cited By ~ 66

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.

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Expression of Xenopus N-CAM RNA in ectoderm is an early response to neural induction

Development ◽

10.1242/dev.99.3.311 ◽

1987 ◽

Vol 99 (3) ◽

pp. 311-325 ◽

Cited By ~ 70

Author(s):

C.R. Kintner ◽

D.A. Melton

Keyword(s):

Neural Development ◽

Transcriptional Activation ◽

Neural Induction ◽

Early Response ◽

Neural Plate ◽

Cdna Clones ◽

Epidermal Tissue ◽

Early Expression ◽

Neural Ectoderm

We have isolated Xenopus laevis N-CAM cDNA clones and used these to study the expression of N-CAM RNA during neural induction. The results show that the first marked increase in N-CAM RNA levels occurs during gastrulation when mesoderm comes in contact with ectoderm and induces neural development. In situ hybridization results show that the early expression of N-CAM RNA is localized to the neural plate and its later expression is confined to the neural tube. Induction experiments with explanted germ layers show that N-CAM RNA is not expressed in ectoderm unless there is contact with inducing tissue. Together these results suggest an approach to studying how ectoderm is committed to form neural rather than epidermal tissue. Specifically, the data suggest that neural commitment is marked and perhaps mediated by the transcriptional activation of genes, like N-CAM, in the neural ectoderm.

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