Brain enlargement with rostral bias in larvae from a spontaneously occurring female variant line of Xenopus; role of aberrant embryonic Wnt/β-catenin signaling.

Increased brain size and its rostral bias are hallmarks of vertebrate evolution, but the underlying developmental and genetic basis remains poorly understood. To provide clues to understanding vertebrate brain evolution, we investigated the developmental mechanisms of brain enlargement observed in the offspring of a previously unrecognized, spontaneously occurring female variant line of Xenopus that appears to reflect a genetic variation. Brain enlargement in larvae from this line showed a pronounced rostral bias that could be traced back to the neural plate, the primordium of the brain.

FGF/MAPK/Ets signaling in Xenopus ectoderm contributes to neural induction and patterning in an autonomous and paracrine manner, respectively.

FGF and anti-BMP signals from the Spemann organizer of mesodermal origin are essential for Xenopus neural development from gastrula ectoderm. However, the detailed cellular and molecular mechanisms of signaling, especially those underlying the neural induction process, are still controversial. We show here that the expression of early neural marker genes such as sox2 and otx2 is suppressed both in vivo and in vitro, when ectoderm cells are loaded with a dominant-negative construct of Ets transcription factors or a translation-blocking antisense FGF2 MO or FGF8 MO, respectively.

Polypyrimidine tract-binding protein is required for the repression of gene expression by all-trans retinoic acid.

All-trans retinoic acid is a key regulator of early development. High concentrations of retinoic acid interfere with differentiation and migration of neural crest cells. Here we report that a dinucleotide repeat in the cis-element of Snail2 (previously known as Slug) gene plays a role in repression by all-trans retinoic acid.

Competition for ligands between FGFR1 and FGFR4 regulates Xenopus neural development.

Cell-surface-localized receptors and their extracellular ligands usually comprise distinct families and promote diversity of signal transduction regulation. The number of available ligand molecules is often the limiting factor for receptor activation during interpretation of the signal by the responding cell. Limited ligand availability in a particular area of tissue should lead to local competition between different members of a receptor family for binding and subsequent activation.

Expression cloning of Xenopus zygote arrest 2 (Xzar2) as a novel epidermalization-promoting factor in early embryos of Xenopus laevis.

In vertebrates, BMPs are known to induce epidermal fate at the expense of neural fate. To further explore the molecular mechanisms of epidermal differentiation, we have developed an expression cloning system for isolating cDNAs that encode intrinsic proteins with epidermal-inducing activity. Under our conditions, 92.

Caenorhabditis elegans Rab escort protein (REP-1) differently regulates each Rab protein function and localization in a tissue-dependent manner.

Rab proteins play a critical role in intracellular vesicle trafficking and require post-translational modification by adding lipids at the C-terminus for proper functions. This modification is preceded by the formation of a trimeric protein complex with the Rab escort protein (REP) and the Rab geranylgeranyltransferase (RabGGTase). However, the genetic hierarchy among these proteins and the tissue-specificity of each protein function are not yet clearly understood.

Melatonin signaling regulates locomotion behavior and homeostatic states through distinct receptor pathways in Caenorhabditis elegans.

Melatonin is a hormone that controls circadian rhythms and seasonal behavioral changes in vertebrates. Recent studies indicate that melatonin participates in diverse physiological functions including the modulation of neural activities. Melatonin is also detected in many other organisms that do not exhibit obvious circadian rhythms, but their precise functions are not known.

Involvement of a Xenopus nuclear GTP-binding protein in optic primordia formation.

Using a subtracted Xenopus cDNA library based on the differential sensitivity of anterior and posterior genes to retinoic acid, we isolated a novel Xenopus nuclear GTP-binding protein (XGB). XGB is expressed prominently in the optic primordia at the tailbud stage. The N-terminal region of XGB contains a set of GTP-binding protein motifs, and the C-terminal region contains two putative nuclear localization signals and two coiled regions.

Regulation of Slug transcription in embryonic ectoderm by beta-catenin-Lef/Tcf and BMP-Smad signaling.

Neural crest is formed at the boundary of epidermal and neural ectoderm. To understand the molecular mechanism of neural crest formation, we focused on the transcriptional regulation of the Slug gene. In the upstream sequence of the chicken Slug gene, we have identified potential binding sites for transcription factors, such as Lef/Tcf and Smad1.

Functional role of a novel ternary complex comprising SRF and CREB in expression of Krox-20 in early embryos of Xenopus laevis.

Krox-20, originally identified as a member of "immediate-early" genes, plays a crucial role in the formation of two specific segments in the hindbrain during early development of the vertebrate nervous system. Here we cloned a genomic sequence of Xenopus Krox-20 (XKrox-20) and studied functions of a promoter element in the flanking sequence and associated transcription factors, which function in early Xenopus embryos. Using the luciferase reporter assay system, we showed that the 5' flanking sequence was sufficient to induce luciferase activities when the reporter construct was injected into embryos at the eight-cell stage.

Integration of multiple signal transducing pathways on Fgf response elements of the Xenopus caudal homologue Xcad3.

Early neural patterning along the anteroposterior (AP) axis appears to involve a number of signal transducing pathways, but the precise role of each of these pathways for AP patterning and how they are integrated with signals that govern neural induction step is not well understood. We investigate the nature of Fgf response element (FRE) in a posterior neural gene, Xcad3 (Xenopus caudal homologue) that plays a crucial role of posterior neural development. We provide evidence that FREs of Xcad3 are widely dispersed in its intronic sequence and that these multiple FREs comprise Ets-binding and Tcf/Lef-binding motifs that lie in juxtaposition.