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Using an expression cloning strategy that relies on a functional assay, we have cloned a novel Xenopus homeobox-containing gene, Siamois. Embryos injected in a ventral-vegetal blastomere with as little as 5 pg of Siamois mRNA develop a complete secondary axis, but the progeny of the injected cells do not participate in the secondary axis formation. In(More)
The first chordates appear in the fossil record at the time of the Cambrian explosion, nearly 550 million years ago. The modern ascidian tadpole represents a plausible approximation to these ancestral chordates. To illuminate the origins of chordate and vertebrates, we generated a draft of the protein-coding portion of the genome of the most studied(More)
Although the proteins that read the gene regulatory code, transcription factors (TFs), have been largely identified, it is not well known which sequences TFs can recognize. We have analyzed the sequence-specific binding of human TFs using high-throughput SELEX and ChIP sequencing. A total of 830 binding profiles were obtained, describing 239 distinctly(More)
Siamois, a Xenopus zygotic homeobox gene with strong dorsalising activity, is expressed in the dorsal-vegetal organiser known as the Nieuwkoop centre. We show that, in contrast to Spemann organiser genes such as goosecoid, chordin and noggin, Siamois gene expression is not induced following overexpression of mesoderm inducers in ectodermal (animal cap)(More)
The choice/no-choice method provides a means of obtaining unbiased estimates of the performance characteristics of strategies. The three experiments in the study illustrate the method's usefulness for testing predictions of alternative models of strategy choice. The experiments focused on 20- and 70-year-olds' choices among mental calculation, use of a(More)
This study reports a longitudinal investigation of French 2nd graders' acquisition of single-digit multiplication skill. Speed, accuracy, and strategy use were assessed 3 times within the year when children learned multiplication. The data showed that improvements in speed and accuracy that generally accompany learning can reflect at least 4 types of(More)
Although an induction event is required for the formation of mesoderm in Xenopus embryos, it is not clear that this induction is wholly sufficient to give rise to a correctly patterned mesodermal layer. We have studied the expression of the two genes, goosecoid and Xwnt-8, in Xenopus gastrulae in which cell-cell communication, and therefore mesoderm(More)
Neural induction constitutes the first step in the generation of the vertebrate nervous system from embryonic ectoderm. Work with Xenopus ectodermal explants has suggested that epidermis is induced by BMP signals, whereas neural fates arise by default following BMP inhibition. In amniotes and ascidians, however, BMP inhibition does not appear to be(More)
With little more than 330 cells, two thirds within the sensory vesicle, the CNS of the tadpole larva of the ascidian Ciona intestinalis provides us with a chordate nervous system in miniature. Neurulation, neurogenesis and its genetic bases, as well as the gene expression territories of this tiny constituency of cells all follow a chordate plan, giving rise(More)
BACKGROUND In Xenopus, the endoderm germ layer is derived from the vegetal blastomeres of cleavage-stage embryos. Cell transplantation experiments have revealed that the endodermal fate becomes gradually fixed during the late blastula stages. Sox17alpha, Mix.1, Mixer and GATA-4 encode vegetal zygotic transcription factors with endoderm-inducing activity.(More)