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The zinc finger and BTB domain-containing 11 gene (zbtb11) is expressed in the Xenopus anterior neuroectoderm, but the molecular nature of the Zbtb11 protein during embryonic development remains to be elucidated. Here, we show the role of Zbtb11 in anterior patterning of the neuroectoderm and the cooperative action with the transcription factor Otx2. Both overexpression and knockdown of zbtb11 caused similar phenotypes: expanded expression of the posterior gene gbx2 in the neural plate, and later microcephaly with reduced eyes, suggesting that a proper level of zbtb11 expression is necessary for normal patterning of the neuroectoderm, including eye formation. Co-immunoprecipitation assays showed that Zbtb11 formed a complex with itself and with a phosphomimetic and repressive form of Otx2, suggesting that Zbtb11 forms a dimer or oligomer and interacts with Otx2 in a phosphorylation-dependent manner. Reporter analysis further showed that Zbtb11 enhanced the activity of the phosphomimetic Otx2 to repress a silencer element of the posterior gene meis3. These data suggest that Zbtb11 coordinates with phosphorylated Otx2 to specify the anterior neuroectoderm by repressing posterior genes. [ABSTRACT FROM AUTHOR]

Extracellular factors belonging to the TGF-β family play pivotal roles in the formation and patterning of germ layers during early Xenopus embryogenesis. Here, we show that the vg1 and nodal3 genes of Xenopus laevis are present in gene clusters on chromosomes XLA1L and XLA3L, respectively, and that both gene clusters have been completely lost from the syntenic S chromosome regions. The presence of gene clusters and chromosome-specific gene loss were confirmed by cDNA FISH analyses. Sequence and expression analyses revealed that paralogous genes in the vg1 and nodal3 clusters on the L chromosomes were also altered compared to their Xenopus tropicalis orthologs. X. laevis vg1 and nodal3 paralogs have potentially become pseudogenes or sub-functionalized genes and are expressed at different levels. As X. tropicalis has a single vg1 gene on chromosome XTR1, the ancestral vg1 gene in X. laevis appears to have been expanded on XLA1L. Of note, two reported vg1 genes, vg1(S20) and vg1(P20), reside in the cluster on XLA1L. The nodal3 gene cluster is also present on X. tropicalis chromosome XTR3, but phylogenetic analysis indicates that nodal3 genes in X. laevis and X. tropicalis were independently expanded and/or evolved in concert within each cluster by gene conversion. These findings provide insights into the function and molecular evolution of TGF-β family genes in response to allotetraploidization.

The interplay between transcription factors and chromatin dictates gene regulatory network activity. Germ layer specification is tightly coupled with zygotic gene activation and, in most metazoans, is dependent upon maternal factors. We explore the dynamic genome-wide interactions of Foxh1, a maternal transcription factor that mediates Nodal/TGF-β signaling, with cis-regulatory modules (CRMs) during mesendodermal specification. Foxh1 marks CRMs during cleavage stages and recruits the co-repressor Tle/Groucho in the early blastula. We highlight a population of CRMs that are continuously occupied by Foxh1 and show that they are marked by H3K4me1, Ep300, and Fox/Sox/Smad motifs, suggesting interplay between these factors in gene regulation. We also propose a molecular "hand-off" between maternal Foxh1 and zygotic Foxa at these CRMs to maintain enhancer activation. Our findings suggest that Foxh1 functions at the top of a hierarchy of interactions by marking developmental genes for activation, beginning with the onset of zygotic gene expression.

To explore the origins and consequences of tetraploidy in the African clawed frog, we sequenced the Xenopus laevis genome and compared it to the related diploid X. tropicalis genome. We characterize the allotetraploid origin of X. laevis by partitioning its genome into two homoeologous subgenomes, marked by distinct families of 'fossil' transposable elements. On the basis of the activity of these elements and the age of hundreds of unitary pseudogenes, we estimate that the two diploid progenitor species diverged around 34 million years ago (Ma) and combined to form an allotetraploid around 17-18 Ma. More than 56% of all genes were retained in two homoeologous copies. Protein function, gene expression, and the amount of conserved flanking sequence all correlate with retention rates. The subgenomes have evolved asymmetrically, with one chromosome set more often preserving the ancestral state and the other experiencing more gene loss, deletion, rearrangement, and reduced gene expression.

In the K1.8 beam-line at Hadron Experimental Facility of J-PARC, a new magnetic spectrometer S-2S is being installed. S-2S was designed to achieve a high momentum resolution of Δp/p = 6 × 10−4 in FWHM. Several strangeness-physics programs which require the high resolution will be realized by S-2S. The present article introduces J-PARC E70 (missing-mass spectroscopy of Ξ12Be) and E94 (missing-mass spectroscopy of Λ7Li, Λ10B, and Λ12C) experiments.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ydbio.2005.10.043 Byline: Young Ryun Cha, Shuji Takahashi, Christopher V.E. Wright Keywords: Morpholino; Xnr; Xlefty/Xantivin; Xbrachyury; Organizer; Mesendoderm induction; Gastrulation; Xenopus laevis Abstract: Dynamic spatiotemporal expression of the nodal gene and its orthologs is involved in the dose-dependent induction and patterning of mesendoderm during early vertebrate embryogenesis. We report loss-of-function studies that define a high degree of synergistic negative regulation on the Xenopus nodal-related genes (Xnrs) by extracellular Xenopus antivin/lefty (Xatv/Xlefty)-mediated functional antagonism and Brachyury-mediated transcriptional suppression. A strong knockdown of Xlefty/Xatv function was achieved by mixing translation- and splicing-blocking morpholino oligonucleotides that target both the A and B alloalleles of Xatv. Secreted and cell-autonomous inhibitors of Xnr signaling were used to provide evidence that Xnr-mediated induction was inherently long-range in this situation in the large amphibian embryo, essentially being capable of spreading over the entire animal hemisphere. There was a greater expansion of the Organizer and mesendoderm tissues associated with dorsal specification than noted in previous Xatv knockdown experiments in Xenopus, with consequent exogastrulation and long-term maintenance of expanded axial tissues. Xatv deficiency caused a modest animal-ward expansion of the marginal zone expression territory of the Xnr1 and Xnr2 genes. In contrast, introducing inhibitory Xbra-En.sup.R fusion constructs into Xatv-deficient embryos caused a much larger increase in the level and spatial extent of Xnr expression. However, in both cases (Xatv/Xlefty-deficiency alone, or combined with Xbra interference), Xnr2 expression was constrained to the superficial cell layer, suggesting a fundamental tissue-specific competence in the ability to express Xnrs, an observation with direct implications regarding the induction of endodermal vs. mesodermal fates. Our experiments reveal a two-level suppressive mechanism for restricting the level, range, and duration of Xnr signaling via extracellular inhibition by Xatv/Xlefty coupled with potent indirect transcriptional repression by Xbra. Author Affiliation: Department of Cell and Developmental Biology, Program in Developmental Biology, Vanderbilt University School of Medicine, 465 21st Avenue South, Nashville, TN 37232, USA Article History: Received 2 August 2005; Revised 20 October 2005; Accepted 28 October 2005

Neural differentiation is induced by inhibition of BMP signaling. Secreted inhibitors of BMP such as Chordin from the Spemann organizer contribute to the initial step of neural induction. Xenopus Smad-interacting protein-1 gene (XSIP1) is expressed in neuroectoderm from the early gastrula stage through to the neurula stage. XSIPI is able to inhibit BMP signaling and overexpression of XS1PI induces neural differentiation. To clarify the function of XSIP1 in neural differentiation, we performed a loss-of-function study of XSIP1. Knockdown of XSIP1 inhibited SoxD expression and neural differentiation. These results indicate that XS1P1 is essential for neural induction. Furthermore, loss-of-function experiments showed that SoxD is essential for XSIP1 transcription and for neural differentiation. However, inhibition of XSIP1 translation prevented neural differentiation induced by SoxD; thus, SoxD was not sufficient to mediate neural differentiation. Expression of XSIPI was also required for inhibition of BMP signaling. Together, these results suggest that XSIP1 and SoxD interdependently function to maintain neural differentiation. Keywords: XSIP1; Xenopus; Neural induction; [delta]EF1/ZFH family; SoxD; BMP; Zinc finger

In vertebrates, nodal-related genes are crucial for specifying mesendodermal cell fates. Six nodal-related genes have been identified in Xenopus, but only one, nodal, has been identified in the mouse. The Xenopus nodal-related gene 3 (Xnr3), however, lacks the mesoderminducing activity of the other five nodal-related genes in Xenopus, and can directly induce neural tissue in animal caps by antagonizing BMP signals. In this study, we isolated three clones of the Xenopus (Silurana) tropicalis nodal-related gene 3 (Xmr3) and analyzed their function. The Xtnr3 genes show high homology to Xnr3 and have the same activity. Southern blot and genomic PCR analyses indicate that the X. tropicalis genome has duplications in the Xtnr3 gene sequences and our three clones represent separate gene loci. We also found a partial clone of Xtnr3 that coded for the N-terminal part of its pro-region. Surprisingly, this sequence also induced neural tissue by antagonizing BMP signals, and its coded protein physically associated with BMP4 mature protein. Furthermore, we showed that the pro-region of Xnr5 has the same activity. Together, these findings indicate that the pro-region of nodal-related genes acts antagonistically towards BMP signals, which identifies a novel mechanism for the inhibition of BMP signaling. [c] 2003 Elsevier Inc. All rights reserved. Keywords: Xnr3; Nodal; BMP; TGF-[beta] superfamily; Pro-region; Neural induction; Xenopus laevis; Xenopus tropicalis

Four nodal-related genes (Xnr1-4) have been isolated in Xenopus to date, and we recently further identified two more, Xnr5 and Xnr6. In the present functional study, we constructed cleavage mutants of Xnr5 (cmXnr5) and Xnr6 (cmXnr6) which were expected to act in a dominant-negative manner. Both cmXnr5 and cmXnr6 inhibited the activities of Xnr5 and Xnr6 in co-overexpression experiments, cmXnr5 also inhibited the activity of Xnr2, Xnr4, Xnr6, derriere, and BVg1, but did not inhibit the activity of Xnr1 or activin. Misexpression of cmXnr5 led to a severe delay in initiation of gastrulation and phenotypic changes, including defects in anterior structures, which were very similar to those seen in maternal VegT-depleted embryos. Further, although the expression of Xnr1, Xnr2, and Xnr4 was not delayed in these embryos, it was markedly reduced. Injection of cmXnr5 had no notable effect on expression of Xnr3, Xnr6, derriere, or siamois. Several mesodermal and endodermal markers also showed delayed and decreased expression during gastrulation in cmXnr5-injected embryos. These results suggest that, in early Xenopus embryogenesis, nodal-related genes may heterodimerize with other TGF-[beta] ligands, and further that one nodal-related gene alone is insufficient for mesendoderm formation, which may require the cooperative interaction of multiple nodal-related genes. Key Words: nodal; cleavage mutant; Xenopus; TGF-[beta] superfamily; Xnr5; Xnr6.

Amyloid precursor protein (APP), which gives rise to the amyloid beta/A4 protein known to form tissue deposits in the brains of patients with Alzheimer's disease, builds a complex by acting as a receptor to G-O, a GTP-binding protein in the brain. GTP-gamma-S caused APP to fail to react to G-O. It is therefore feasible that Alzheimer's disease results from the malfunctioning of the APP-G-O system produced by structural changes in APP.