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Retinoids regulate gene expression via nuclear retinoic acid receptors, the RARs and RXRs. To investigate the functions of retinoid receptors during early neural development, we expressed a dominant negative RARbeta in early Xenopus embryos. We obtained evidence that dominant negative RARbeta specifically inhibits RAR/RXR heterodimer-mediated, but not RXR(More)
Inductive cell interactions are essential in early embryonic development, but virtually nothing is known about the molecular mechanisms involved. Recently factors resembling fibroblast growth factor and transforming growth factor-beta were shown to be involved in mesoderm induction in Xenopus laevis, suggesting that membrane receptor-mediated signal(More)
The purpose of this study was to make an explicit test of the idea that a retinoid could act as a morphogen, differentially activating genes and specifying anteroposterior (a-p) level in the developing vertebrate central nervous system (CNS). Our approach was to characterize the concentration-dependent effects of retinoic acid (RA) on the neural expression(More)
A previous version of this work was presented as a paper at RIAO 97 conference in Quebec, Canada and included in RIAO 97 proceedings (Arampatzis et al., 1997a). Abstract In this article we describe a retrieval schema which goes beyond the classical information retrieval keyword hypothesis and takes into account also linguistic variation. Guided by the(More)
There is evidence suggesting that pHi elevation can induce differentiation to cement gland, an extremely anterior structure, during the early development of Xenopus laevis (Picard, J. J. (1975) J. Embryol. exp. Morphol. 33, 957-967; Sive, H. L., Hattori, K. and Weintraub, H. (1989) Cell 58, 171-180). We wanted to investigate whether axial development or(More)
Induction of mesoderm during early amphibian embryogenesis can be mimicked in vitro by adding growth factors, including heparin-binding and type-beta transforming growth factors (TGF-beta), to isolated ectoderm explants from Xenopus laevis embryos. Although the mesoderm-inducing factor (MIF) from X. laevis XTC cells (XTC-MIF) has properties similar to(More)
AAx Grammars over a Finite Lattice (agfls), a simple form of two-level grammars admitting quite eecient implementations, are proposed as a formalism to express the syntax of natural languages. In this paper the concepts and notation of agfls are described. A brief example is given of their use in describing a fragment of the English language, followed by a(More)
In this paper a conceptual model for object-oriented analysis is introduced. Three submod-els are described which can be seen as milestones during the analysis phase. Each (sub)model has a corresponding paraphrasing mechanism which may be used (1) to provide a description of the structure of the model and (2) to generate sample instantiations. This(More)
AAx Grammars over a Finite Lattice (agfls), a simple form of two-level grammars admitting quite eecient implementations, are proposed as a formalism to express the syntax of natural languages. In this paper the concepts and notation of agfls are described. A brief example is given of their use in describing a fragment of the English language, followed by a(More)