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The Brachyury (T) gene is required for mesoderm formation in the mouse. In this paper we describe the cloning and expression of a Xenopus homolog of Brachyury, Xbra. As with Brachyury in the mouse, Xbra is expressed in presumptive mesodermal cells around the blastopore, and then in the notochord. We show that expression of Xbra occurs as a result of(More)
The protein XTC-MIF, a Xenopus homologue of activin A and a potent mesoderm-inducing factor, can induce responding animal pole explants to form several different cell types in a dose-dependent manner, higher doses eliciting more dorso-anterior tissues. This graded response, characteristic of classically postulated morphogens, may underlie pattern formation,(More)
The potent mesoderm-inducing factors activin and FGF are present as maternally synthesized proteins in embryos of X. laevis. We show that activin can act on explanted blastomeres to induce at least five different cell states ranging from posterolateral mesoderm to dorsoanterior organizer mesoderm. Each state is induced in a narrow dose range bounded by(More)
The growth factor activin elicits mesodermal fates when applied to prospective ectodermal cells of the Xenopus blastula stage embryo. Previous experiments with dissociated cells showed that there are at least five different responses separated by closely spaced, sharp dose thresholds. Here we investigate this multithreshold activin response further using(More)
Embryonic development requires cell movements whose coordination is robust and reproducible. A dramatic example is the primary body axis of vertebrates: despite perturbation, cells in prospective axial tissue coordinate their movements to make an elongated body axis. The spatial cues coordinating these movements are not known. We show here that cells(More)
In both invertebrate and vertebrate embryonic central nervous systems, deep cells differentiate while superficial (ventricular) epithelial cells remain in a proliferative, stem cell state. The conserved polarity protein PAR-1, which is basolaterally localised in epithelia, promotes and is required for differentiating deep layer cell types, including(More)
The formation of blood in the embryo is dependent on bone morphogenetic protein (BMP), but how BMP signaling intersects with other regulators of hematopoietic development is unclear. Using embryonic stem (ES) cells, we show that BMP4 first induces ventral-posterior (V-P) mesoderm and subsequently directs mesodermal cells toward blood fate by activating(More)
The mesoderm of Xenopus laevis and other amphibia is formed through an inductive interaction during which cells of the vegetal hemisphere act on cells of the animal hemisphere. Two groups of factors mimic the effects of the vegetal hemisphere. One group consists of members of the fibroblast growth factor (FGF) family, while the other is related to(More)
We present direct evidence of an activator-inhibitor system in the generation of the regularly spaced transverse ridges of the palate. We show that new ridges, called rugae, that are marked by stripes of expression of Shh (encoding Sonic hedgehog), appear at two growth zones where the space between previously laid rugae increases. However, inter-rugal(More)