The Role of Maternal VegT in Establishing the Primary Germ Layers in Xenopus Embryos

FoxC1 is an important transcription factor in vertebrate development since its mutation in humans results in Axenfeld-Rieger syndrome. In the mouse, disturbance of its function causes congenital hydrocephalus and abnormalities in the development of various mesodermal derivatives. In this report, we provide one mechanistic basis for the requirement for FoxC1 in vertebrate development. We find that, in Xenopus laevis embryos, FoxC1 expression is regulated by the maternal T-box transcription factor VegT, via the nodal sub-family of TGF␤ signaling transducers. We show that at the late neurula to early tailbud stage, FoxC1 depletion causes the down-regulation of adhesion molecules, EP and E cadherin, as well as members of the Ephrin/EphR signaling families in the mesoderm germ layer resulting in the loss of adhesion and apoptosis of mesodermal cells. Developmental Dynamics 236:2731-2741, 2007.

Section: Affymetrix Analysismentioning

confidence: 99%

“…One major determinant of mesoderm and endodermal fate is the maternal, vegetally located T-box transcription factor VegT (Zhang et al, 1998). VegT directly regulates the earliest expression of zygotic transcription factors and signaling molecules at the late blastula stage when zygotic transcription starts.…”

Section: Introductionmentioning

confidence: 99%

The role of FoxC1 in early Xenopus development

Birsoy

Kofron

et al. 2007

“…3; reviewed in Kavka and Green, 1997). VegT depletion experiments have shown that it is required for the formation of endoderm and the positioning of the other germ layers in the animal-vegetal axis (Zhang et al, 1998). Because there is evidence for both indirect non-cellautonomous action of VegT by means of nodals and direct, cell autonomous action on mesodermal marker genes and that this direct action is dose-dependent (Clements et al, 1999;Kavka and Green, 2000), it may be that VegT serves as an intracellular morphogen, not unlike bicoid in Drosophila (discussed in Kavka and Green, 1997).…”

Section: Early Xenopus Morphogens In Vivo: Not Activin But Nodals?mentioning

confidence: 99%

Morphogen gradients, positional information, and Xenopus: Interplay of theory and experiment

Green

2002

The idea of morphogen gradients has long been an important one in developmental biology. Studies with amphibians and with Xenopus in particular have made significant contributions to demonstrating the existence, identity, and mechanisms of action of morphogens. Mesoderm induction and patterning by activin, nodals, bone morphogenetic proteins, and fibroblast growth factors have been analyzed thoroughly and reveal recurrent and combinatorial roles for these protein growth factor morphogens and their antagonists. The dynamics of nodal-type signaling and the intersection of VegT and ␤-catenin intracellular gradients reveal detailed steps in early long-range patterning. Interpretation of gradients requires sophisticated mechanisms for sharpening thresholds, and the activin-Xbra-Gsc system provides an example of this. The understanding of growth factor signal transduction has elucidated growth factor morphogen action and provided tools for dissecting their direct longrange action and distribution. The physical mechanisms of morphogen gradient establishment are the focus of new interest at both the experimental and theoretical level. General themes and emerging trends in morphogen gradient studies are discussed.

“…The vegetally localized, maternal Tbox transcription factor VegT initiates endoderm formation in Xenopus laevis (Zhang et al, 1998;Xanthos et al, 2001). Vempati and King had previously deposited the full-length sequence of tropicalis VegT (tVegT) in Genbank, which is 93% identical to laevis VegT at the amino acid level.…”

Section: Vegtmentioning

confidence: 99%

“…VegT activity results in the transcription of zygotic endodermal genes (Zhang et al, 1998;Clements et al, 1999;Xanthos et al, 2001), which include the following: nodalrelated proteins (Xnr1,2,4,5,6) and derriere, which are members of the transforming growth factor-beta (TGF␤) growth factor family (Jones et al, 1995;Joseph and Melton, 1997;Sun et al, 1999;Takahashi et al, 2000); homeodomain proteins of the Mixer/Mix/Bix family (Rosa, 1989;Vize, 1996;Henry and Melton, 1998;Tada et al, 1998;Casey et al, 1999); the zinc finger factors Gata 4, 5, and 6 (Jiang and Evans, 1996;Weber et al, 2000;Xanthos et al, 2001); and two closely related HMG domain transcription factors, Sox17␣ and Sox17␤ (Husdon et al, 1997).…”

Section: Introductionmentioning

confidence: 99%

Molecular components of the endoderm specification pathway in Xenopus tropicalis

D'Souza

Lee

Taverner

et al. 2002

Xenopus laevis has been instrumental in elucidating a conserved molecular pathway that regulates vertebrate endoderm specification. However, loss-of-function analysis is required to resolve the precise function of the genes involved. For such analysis, antisense oligos and possibly forward genetics are likely to be more effective in the diploid species Xenopus tropicalis than in the pseudotetraploid Xenopus laevis. Here we have isolated most of the tropicalis genes in the endoderm specification pathway, specifically, tVegT, tMixer, tMix, tBix, tGata6, tSox17␣, tSox17␤, tFoxA1, tHex, and tCerberus, which lack the redundant copies that are found in laevis. In situ hybridization analysis has revealed identical expression patterns between the orthologous tropicalis and laevis endoderm genes, thus suggesting conserved genetic functions. Furthermore, we noted that the smaller tropicalis embryos gave better probe penetration than in laevis whole-mount in situ hybridizations-allowing us to visualize transcripts in the deep endoderm in tropicalis, which is difficult in laevis. This study illustrates how an entire genetic pathway can be quickly transferred from laevis to tropicalis due to high sequence conservation between the sister species and the large number of tropicalis-expressed sequence tags that are now available.