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Title: Xmc, a novel Xenopus laevis organiser gene regulating gastrulation movements
Author: Frazzetto, Giovanni
ISNI:       0000 0001 3483 6306
Awarding Body: University of London
Current Institution: University College London (University of London)
Date of Award: 2002
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The Xenopus (or Spemann-Mangold) organiser is a powerful signalling centre responsible for establishing the main body plan. It instructs indifferent, competent tissue to follow certain paths of development: it neuralises ectoderm and dorsalises mesoderm and endoderm. In addition to its inductive capabilities, the organiser governs the morphogenetic movements occurring during gastrulation. Gastrulation in vertebrates is a highly dynamic process, driven mainly by convergent extension of internal mesodermal cells, by which all three germ layers are patterned within an embryo with recognizable antero-posterior and dorso-ventral polarity. In search for genes expressed in the organiser, an in situ hybridisation screen was carried out on a cDNA subtracted library enriched for organiser genes. Such library was constructed by Suppressive Subtractive Hybridisation, subtracting a Dorsal Marginal Zone cDNA population with an egg cDNA population. 6% of the genes isolated in the screen exhibited differential expression in the organiser. One of them was termed Xmc, an acronym for Xenopus marginal coil. Xmc encodes a protein containing two widely spaced evolutionarily non-conserved coiled coils. Immuno-localisation studies reveal Xmc protein is found in vesicular aggregates in the cytoplasm and associated with the inner plasma membrane. Xmc is expressed in a dynamic fashion around the blastoporal circumpherence, in mesodermal cells undergoing morphogenetic movements, in a pattern similar to bona fide FGF target genes. Likewise, Xmc expression can be induced by ectopic XeFGF signalling and the early mesodermal expression is dependent on FGF receptor-mediated signaling. Morpholino-mediated translational "knock-down" of Xmc results in embryos that display a reduced elongation of the antero-posterior axis and in a pronounced inhibition of convergent extension movements in embryos and dorsal marginal zone explants. The execution of convergent extension movements normally relies to accurate formation and differentiation of mesodermal tissue. Xmc loss-of-function does not interfere with mesoderm induction or maintenance per se. These results suggest that Xmc is a novel FGF target gene that is specifically required for morphogenetic movements during gastrulation in Xenopus, but is dispensable for the concomitant patterning of mesoderm.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Xenopus marginal coil