To explore the origins and consequences of tetraploidy in the African clawed frog, we sequenced the Xenopus laevis genome and compared it to the related diploid X. tropicalis genome. We demonstrate the allotetraploid origin of X. laevis by partitioning its genome into two homeologous subgenomes, marked by distinct families of “fossil” transposable elements. Based on the activity of these elements and the age of hundreds of unitary pseudogenes, we estimate that the two diploid progenitor species diverged ~34 million years ago (Mya) and combined to form an allotetraploid ~17–18 Mya. 56% of all genes are retained in two homeologous copies. Protein function, gene expression, and the amount of flanking conserved sequence all correlate with retention rates. The subgenomes have evolved asymmetrically, with one chromosome set more often preserving the ancestral state and the other experiencing more gene loss, deletion, rearrangement, and reduced gene expression.

No abstract

No abstract

␤-Catenin is efficiently phosphorylated by glycogen synthase kinase-3␤ in the Axin complex in the cytoplasm, resulting in the down-regulation. In response to Wnt, ␤-catenin is stabilized and translocated into the nucleus where it stimulates gene expression through Tcf/Lef. Here we report a novel protein, designated Duplin (for axis duplication inhibitor), which negatively regulates the function of ␤-catenin in the nucleus. Duplin was located in the nucleus. Duplin bound directly to the Armadillo repeats of ␤-catenin, thereby inhibiting the binding of Tcf to ␤-catenin. It did not affect the stability of ␤-catenin but inhibited Wnt-or ␤-catenin-dependent Tcf activation. Furthermore, expression of Duplin in Xenopus embryos inhibited the axis formation and ␤-catenin-dependent axis duplication, and prevented the ␤-catenin's ability to rescue ventralizing phenotypes induced by ultraviolet light irradiation. Thus, Duplin is a nuclear protein that inhibits ␤-catenin signaling.

No abstract

No abstract

Axam has been identified as a novel Axin-binding protein that inhibits the Wnt signaling pathway. We studied the molecular mechanism by which Axam stimulates the downregulation of ␤-catenin.

No abstract