title: Nodal-related gene Xnr5 is amplified in the Xenopus genome.
abstract: In Xenopus, six nodal-related genes (Xnrs) have been identified to date. We found numerous tandem duplications of Xnr5 in the Xenopus laevis and Xenopus tropicalis genomes that involve highly conserved copies of coding and regulatory regions. The duplicated versions of Xnr5 were expressed in both the superficial and deep layer of dorsal endoderm and in the deep layer of ventral endoderm, where the initial inducers of mesendoderm formation would be expected to be localized. Overexpression of secreted inhibitors of Xnrs led to a substantially enhanced transcription of the duplicated Xnr5 genes and Xnr6 in embryos. Therefore, Xnr5 and Xnr6 have a novel feedback loop to inhibit transcription of Xnr5 and Xnr6. These results suggest that the initialization of a strong Xnr5 and Xnr6 signal is enabled by the rapid transcription from multiple genes. The novel feedback loop may negatively regulate transcription of Xnr5s and Xnr6 to limit overproduction of these potent inducers, with the Xnr5/Xnr6 signal then activating positive (Xnrs) and negative (Xlefty) loops, which regulate the range of mesodermal tissues produced.
authors.affiliation: Department of Cell and Developmental Biology, Program in Developmental Biology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-8240, USA.
authors.forename: Shuji
authors.initials: S
authors.lastname: Takahashi
authors.forename: Yasuko
authors.initials: Y
authors.lastname: Onuma
authors.forename: Chika
authors.initials: C
authors.lastname: Yokota
authors.forename: Joby J
authors.initials: JJ
authors.lastname: Westmoreland
authors.forename: Makoto
authors.initials: M
authors.lastname: Asashima
authors.forename: Christopher V E
authors.initials: CV
authors.lastname: Wright
mesh_terms: D000818:Animals; D001483:Base Sequence; D018076:DNA, Complementary / Q000302:isolation & purification; D004625:Embryo, Nonmammalian; D005784:Gene Amplification; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D014644:Genetic Variation; D055458:Left-Right Determination Factors; D008969:Molecular Sequence Data; D055456:Nodal Signaling Ligands; D012689:Sequence Homology, Nucleic Acid; D016212:Transforming Growth Factor beta / Q000378:metabolism; D029867:Xenopus Proteins / Q000235:genetics* / Q000302:isolation & purification; D014982:Xenopus laevis / Q000235:genetics*
chemical_list: D018076:DNA, Complementary; D055458:Left-Right Determination Factors; D055456:Nodal Signaling Ligands; D016212:Transforming Growth Factor beta; D029867:Xenopus Proteins; C418882:nodal5 protein, Xenopus