A role for the vegetally expressed Xenopus gene Mix.1 in endoderm formation and in the restriction of mesoderm to the marginal zone

Development ◽  
1998 ◽  
Vol 125 (13) ◽  
pp. 2371-2380 ◽  
Author(s):  
P. Lemaire ◽  
S. Darras ◽  
D. Caillol ◽  
L. Kodjabachian
Keyword(s):  
Marginal Zone ◽  
Ectopic Expression ◽  
Homeobox Gene ◽  
Early Response ◽  
Endoderm Differentiation ◽  
Head Formation ◽  
Mutual Repression ◽  
Regulatory Loop ◽  
Strong Activator

We have studied the role of the activin immediate-early response gene Mix.1 in mesoderm and endoderm formation. In early gastrulae, Mix.1 is expressed throughout the vegetal hemisphere, including marginal-zone cells expressing the trunk mesodermal marker Xbra. During gastrulation, the expression domains of Xbra and Mix.1 become progressively exclusive as a result of the establishment of a negative regulatory loop between these two genes. This mutual repression is important for the specification of the embryonic body plan as ectopic expression of Mix.1 in the Xbra domain suppresses mesoderm differentiation. The same effect was obtained by overexpressing VP16Mix.1, a fusion protein comprising the strong activator domain of viral VP16 and the homeodomain of Mix.1, suggesting that Mix.1 acts as a transcriptional activator. Mix.1 also has a role in endoderm formation. It cooperates with the dorsal vegetal homeobox gene Siamois to activate the endodermal markers edd, Xlhbox8 and cerberus in animal caps. Conversely, vegetal overexpression of enRMix.1, an antimorphic Mix.1 mutant, leads to a loss of endoderm differentiation. Finally, by targeting enRMix.1 expression to the anterior endoderm, we could test the role of this tissue during embryogenesis and show that it is required for head formation.

A novel Xenopus mix-like gene milk involved in the control of the endomesodermal fates

Development ◽  
1998 ◽  
Vol 125 (14) ◽  
pp. 2577-2585 ◽  
Author(s):  
V. Ecochard ◽  
C. Cayrol ◽  
S. Rey ◽  
F. Foulquier ◽  
D. Caillol ◽  
...  
Keyword(s):  
Marginal Zone ◽  
Ectopic Expression ◽  
Homeobox Gene ◽  
Early Response ◽  
Response Gene ◽  
Mesodermal Cell ◽  
Early Response Gene ◽  
Mesoderm Formation ◽  
Definition Of ◽  
Early Gastrula

Here we describe a novel Xenopus homeobox gene, milk, related by sequence homology and expression pattern to the vegetally expressed Mix.1. As is the case with Mix.1, milk is an immediate early response gene to the mesoderm inducer activin. milk is expressed at the early gastrula stage in the vegetal cells, fated to form endoderm, and in the marginal zone fated to form mesoderm. During gastrulation, expression of milk becomes progressively reduced in the involuting mesodermal cells but is retained in the endoderm, suggesting that it may play a key role in the definition of the endo-mesodermal boundary in the embryo. Overexpression of milk in the marginal zone blocks mesodermal cell involution, represses the expression of several mesodermal genes such as Xbra, goosecoid, Xvent-1 or Xpo and increases the expression of the endodermal gene, endodermin. In the dorsal marginal zone, overexpression of milk leads to a severe late phenotype including the absence of axial structures. Ectopic expression of milk in the animal hemisphere or in ectodermal explants induces a strong expression of endodermin. Taken together, we propose that milk plays a role in the correct patterning of the embryo by repressing mesoderm formation and promoting endoderm identity.

Suppression of GATA factor activity causes axis duplication in Xenopus

Development ◽  
1998 ◽  
Vol 125 (23) ◽  
pp. 4595-4605 ◽  
Author(s):  
T.G. Sykes ◽  
A.R. Rodaway ◽  
M.E. Walmsley ◽  
R.K. Patient
Keyword(s):  
Cell Fate ◽  
Homeobox Gene ◽  
Dominant Negative ◽  
Gata Factor ◽  
Dorsoventral Axis ◽  
Morphogenetic Protein ◽  
Head Formation ◽  
Bmp Signalling ◽  
Bmp Antagonist

In Xenopus, the dorsoventral axis is patterned by the interplay between active signalling in ventral territories, and secreted antagonists from Spemann's organiser. Two signals are important in ventral cells, bone morphogenetic protein-4 (BMP-4) and Wnt-8. BMP-4 plays a conserved role in patterning the vertebrate dorsoventral axis, whilst the precise role of Wnt-8 and its relationship with BMP-4, are still unclear. Here we have investigated the role played by the GATA family of transcription factors, which are expressed in ventral mesendoderm during gastrulation and are required for the differentiation of blood and endodermal tissues. Injection ventrally of a dominant-interfering GATA factor (called G2en) induced the formation of secondary axes that phenocopy those induced by the dominant-negative BMP receptor. However, unlike inhibiting BMP signalling, inhibiting GATA activity in the ectoderm does not lead to neuralisation. In addition, analysis of gene expression in G2en injected embryos reveals that at least one known target gene for BMP-4, the homeobox gene Vent-2, is unaffected. In contrast, the expression of Wnt-8 and the homeobox gene Vent-1 is suppressed by G2en, whilst the organiser-secreted BMP antagonist chordin becomes ectopically expressed. These data therefore suggest that GATA activity is essential for ventral cell fate and that subsets of ventralising and dorsalising genes require GATA activity for their expression and suppression, respectively. Finally, using G2en, we show that suppression of Wnt-8 expression, in conjunction with blocked BMP signalling, does not lead to head formation, suggesting that the head-suppressing Wnt signal may not be Wnt-8.

Anterior neurectoderm is progressively induced during gastrulation: the role of the Xenopus homeobox gene orthodenticle

Development ◽  
1995 ◽  
Vol 121 (4) ◽  
pp. 993-1004 ◽  
Author(s):  
I.L. Blitz ◽  
K.W. Cho
Keyword(s):  
Expression Patterns ◽  
Functional Characterization ◽  
Ectopic Expression ◽  
Homeobox Gene ◽  
Neural Induction ◽  
Cement Gland ◽  
Spemann's Organizer ◽  
Vertical Contact

In order to study the regional specification of neural tissue we isolated Xotx2, a Xenopus homolog of the Drosophila orthodenticle gene. Xotx2 is initially expressed in Spemann's organizer and its expression is absent in the ectoderm of early gastrulae. As gastrulation proceeds, Xotx2 expression is induced in the overlying ectoderm and this domain of expression moves anteriorly in register with underlying anterior mesoderm throughout the remainder of gastrulation. The expression pattern of Xotx2 suggests that a wave of Xotx2 expression (marking anterior neurectoderm) travels through the ectoderm of the gastrula with the movement of underlying anterior (prechordal plate) mesoderm. This expression of Xotx2 is reminiscent of the Eyal-Giladi model for neural induction. According to this model, anterior neural-inducing signals emanating from underlying anterior mesoderm transiently induce anterior neural tissues after vertical contact with the overlying ectoderm. Further patterning is achieved when the ectoderm receives caudalizing signals as it comes in contact with more posterior mesoderm during subsequent gastrulation movements. Functional characterization of the Xotx2 protein has revealed its involvement in differentiation of the anterior-most tissue, the cement gland. Ectopic expression of Xotx2 in embryos induces extra cement glands in the skin as well as inducing a cement gland marker (XAG1) in isolated animal cap ectoderm. Microinjection of RNA encoding the organizer-specific homeo-domain protein goosecoid into the ventral marginal zone results in induction of the Xotx2 gene. This result, taken in combination with the indistinguishable expression patterns of Xotx2 and goosecoid in the anterior mesoderm suggests that Xotx2 is a target of goosecoid regulation.

The role of the msh homeobox gene during Drosophila neurogenesis: implication for the dorsoventral specification of the neuroectoderm

Development ◽  
1997 ◽  
Vol 124 (16) ◽  
pp. 3099-3109 ◽  
Author(s):  
T. Isshiki ◽  
M. Takeichi ◽  
A. Nose
Keyword(s):  
Cell Fate ◽  
Neural Development ◽  
Ectopic Expression ◽  
Homeobox Gene ◽  
Loss Of Function ◽  
Spinal Cord Development ◽  
Dorsal Portion ◽  
Msx Genes

Development of the Drosophila central nervous system begins with the delamination of neural and glial precursors, called neuroblasts, from the neuroectoderm. An early and important step in the generation of neural diversity is the specification of individual neuroblasts according to their position. In this study, we describe the genetic analysis of the msh gene which is likely to play a role in this process. The msh/Msx genes are one of the most highly conserved families of homeobox genes. During vertebrate spinal cord development, Msx genes (Msx1-3) are regionally expressed in the dorsal portion of the developing neuroectoderm. Similarly in Drosophila, msh is expressed in two longitudinal bands that correspond to the dorsal half of the neuroectoderm, and subsequently in many dorsal neuroblasts and their progeny. We showed that Drosophila msh loss-of-function mutations led to cell fate alterations of neuroblasts formed in the dorsal aspect of the neuroectoderm, including a possible dorsal-to-ventral fate switch. Conversely, ectopic expression of msh in the entire neuroectoderm severely disrupted the proper development of the midline and ventral neuroblasts. The results provide the first in vivo evidence for the role of the msh/Msx genes in neural development, and support the notion that they may perform phylogenetically conserved functions in the dorsoventral patterning of the neuroectoderm.

The Homeobox Gene cut Interacts Genetically With the Homeotic Genes proboscipedia and Antennapedia

Genetics ◽  
1998 ◽  
Vol 149 (1) ◽  
pp. 131-142
Author(s):  
Laura A Johnston ◽  
Bruce D Ostrow ◽  
Christine Jasoni ◽  
Karen Blochlinger
Keyword(s):  
Expression Patterns ◽  
Significant Proportion ◽  
Ectopic Expression ◽  
Homeobox Gene ◽  
Homeodomain Protein ◽  
Homeotic Genes ◽  
Loss Of Function ◽  
Regulation Of Expression ◽  
Segmental Identity

Abstract The cut locus (ct) codes for a homeodomain protein (Cut) and controls the identity of a subset of cells in the peripheral nervous system in Drosophila. During a screen to identify ct-interacting genes, we observed that flies containing a hypomorphic ct mutation and a heterozygous deletion of the Antennapedia complex exhibit a transformation of mouthparts into leg and antennal structures similar to that seen in homozygous proboscipedia (pb) mutants. The same phenotype is produced with all heterozygous pb alleles tested and is fully penetrant in two different ct mutant backgrounds. We show that this phenotype is accompanied by pronounced changes in the expression patterns of both ct and pb in labial discs. Furthermore, a significant proportion of ct mutant flies that are heterozygous for certain Antennapedia (Antp) alleles have thoracic defects that mimic loss-of-function Antp phenotypes, and ectopic expression of Cut in antennal discs results in ectopic Antp expression and a dominant Antp-like phenotype. Our results implicate ct in the regulation of expression and/or function of two homeotic genes and document a new role of ct in the control of segmental identity.

Xenopus VegT RNA is localized to the vegetal cortex during oogenesis and encodes a novel T-box transcription factor involved in mesodermal patterning

Development ◽  
1996 ◽  
Vol 122 (12) ◽  
pp. 4119-4129 ◽  
Author(s):  
J. Zhang ◽  
M.L. King
Keyword(s):  
Transcription Factor ◽  
Xenopus Oocytes ◽  
Nuclear Protein ◽  
Marginal Zone ◽  
Ectopic Expression ◽  
Developmental Pathways ◽  
T Box ◽  
Vegetal Cortex ◽  
Head Formation ◽  
Lateral Mesoderm

An RNA localized to the vegetal cortex of Xenopus oocytes encodes a novel T-box protein (VegT) capable of inducing either dorsal or posterior ventral mesoderm at different times in development. VegT is a nuclear protein and its C-terminal domain can activate transcription in a yeast reporter assay, observations consistent with VegT functioning as a transcription factor. Zygotic expression is dynamic along the dorsoventral axis, with transcripts first expressed in the dorsal marginal zone. By the end of gastrulation, VegT is expressed exclusively in posterior ventral and lateral mesoderm and is excluded from the notochord. Later expression is confined to a subset of Rohon-Beard cells, a type of primary sensory neuron. In animal cap assays, VegT is capable of converting prospective ectoderm into ventral lateral mesoderm. Such ectopic expression of VegT induces its own expression as well as that of Xwnt-8 in caps, suggesting that a Wnt pathway may be involved. Mis-expression of VegT in dorsal animal blastomeres fated to contribute to brain suppresses head formation. Our results suggest that VegT is a localized transcription factor, which operates sequentially in several developmental pathways during embryogenesis, including dorsoventral and posterior patterning of mesoderm.

Activating and repressing signals in head development: the role of Xotx1 and Xotx2

Development ◽  
1997 ◽  
Vol 124 (9) ◽  
pp. 1733-1743 ◽  
Author(s):  
M. Andreazzoli ◽  
M. Pannese ◽  
E. Boncinelli
Keyword(s):  
Retinoic Acid ◽  
Ectopic Expression ◽  
Convergent Extension ◽  
Negative Interference ◽  
Head Development ◽  
Tail Development ◽  
Head Formation ◽  
Organizer Activity ◽  
Tail Organizer

Xotx1 and Xotx2 are two Xenopus homologues of the Drosophila orthodenticle gene that are specifically expressed in presumptive head regions that do not undergo convergent extension movements during gastrulation. We studied the function of Xotx1 and compared it with that of Xotx2. Ectopic expression of each of the two genes has similar effects in impairing trunk and tail development. Experimental evidence suggests that posterior deficiencies observed in microinjected embryos are due to negative interference with convergent extension movements. Transplantations of putative tail-forming regions showed that, while Xotx1 overexpression inhibits tail organizer activity, Xotx2 overexpression is able to turn a tail organizer into a head organizer. Finally, Xotx1 and Xotx2 are activated by factors involved in head formation and repressed by a posteriorizing signal like retinoic acid. Taken together, these data suggest that Xotx genes are involved in head-organizing activity. They also suggest that the head organizer may act not only stimulating the formation of anterior regions, but also repressing the formation of posterior structures.

Regional specification of muscle progenitors in Drosophila: the role of the msh homeobox gene

Development ◽  
1998 ◽  
Vol 125 (2) ◽  
pp. 215-223 ◽  
Author(s):  
A. Nose ◽  
T. Isshiki ◽  
M. Takeichi
Keyword(s):  
Progenitor Cells ◽  
Special Class ◽  
Muscle Fibers ◽  
Ectopic Expression ◽  
Homeobox Gene ◽  
Somatic Musculature

The somatic musculature in the abdominal hemisegments of Drosophila consists of 30 uniquely identifiable muscle fibers. Previous studies have suggested that the muscle diversity originates in a special class of myoblasts, called muscle founders, that are formed by the division of muscle progenitors. However, the mechanisms that locate and specify the muscle progenitors/founders are largely unknown. In this study, we first used a novel marker, rP298-LacZ, to chart the development of muscle progenitors/founders during the formation of distinct groups of mature muscles. We then determined the function of the muscle segment homeobox (msh) gene in myogenesis. msh encodes a homeobox-containing protein, vertebrate homologues of which are known as Msxs. We show that msh is expressed in the dorsal and lateral domains of muscle progenitors and is required for the specification of the progenitor cells. Ectopic expression of msh in the entire mesoderm inhibits the proper development of the normally msh-negative muscle progenitors in the dorsolateral domain. These results suggest that msh plays a role in regional specification of muscle progenitors/founders.

Sign in / Sign up

Export Citation Format

Share Document