Browsing by Author "Pandur, P."

The Wnt family of secreted glycoproteins is involved in the regulation of diverse developmental processes. The classical Wnt/beta -catenin pathway has been thoroughly investigated resulting in the identification of a plethora of components involved in the activation of beta -catenin target genes. Moreover, two additional Wnt-triggered pathways have been identified. These various signalling cascades require at least one component that confers signalling specificity. This function is fulfilled at least in part by the Wnt receptor Frizzled. The recent identification of a potential Frizzled co-receptor, an LDL-receptor-related-protein (LRP),((1-3)) sheds more light on Wnt-signal transduction specificity and promises more exciting revelations. BioEssays 23:207-210, 2001. (C) 2001 John Wiley & Sons, Inc.

Popeye genes code for putative transmembrane proteins that are predominantly expressed in heart and skeletal muscle. Here we report on the isolation and expression of a previously unknown Xenopus member of this family, Xenopus Popeye-1 (Xpop-1). Xpop-1 is 60-65% identical to other vertebrate Pop-1 genes at the protein level. Whole-mount in situ hybridization studies revealed a highly specific expression of Xpop-1 whose transcripts are restricted to the embryonic heart and become enriched in the forming ventricle. Interestingly, unlike other known vertebrate Popeye genes, Xpop-1 is exclusively expressed in cardiac tissue and absent from skeletal muscle. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.

Formation of the vertebrate heart requires a complex interplay of several temporally regulated signalling cascades(1). In Xenopus laevis, cardiac specification occurs during gastrulation and requires signals from the dorsal lip and underlying endoderm(2). Among known Xenopus Wnt genes, only Wnt-11 shows a spatiotemporal pattern of expression that correlates with cardiac specification, which indicates that Wnt-11 may be involved in heart development(3,4). Here we show, through loss- and gain-of-function experiments, that XWnt-11 is required for heart formation in Xenopus embryos and is sufficient to induce a contractile phenotype in embryonic explants. Treating the mouse embryonic carcinoma stem cell line P19 with murine Wnt-11 conditioned medium triggers cardiogenesis, which indicates that the function of Wnt-11 in heart development has been conserved in higher vertebrates. XWnt-11 mediates this effect by non-canonical Wnt signalling, which is independent of beta-catenin and involves protein kinase C and Jun amino-terminal kinase. Our results indicate that the cardiac developmental program requires non-canonical Wnt signal transduction.