In Drosophila, planar cell polarity (PCP) signaling is mediated by the receptor Frizzled (Fz) and transduced by Dishevelled (Dsh). Wingless (Wg) signaling also requires Dsh and may utilize DFz2 as a receptor. Using a heterologous system, we show that Dsh is recruited selectively to the membrane by Fz but not DFz2, and this recruitment depends on the DEP domain but not the PDZ domain in Dsh. A mutation in the DEP domain impairs both membrane localization and the function of Dsh in PCP signaling, indicating that translocation is important for function. Further genetic and molecular analyses suggest that conserved domains in Dsh function differently during PCP and Wg signaling, and that divergent intracellular pathways are activated. We propose that Dsh has distinct roles in PCP and Wg signaling. The PCP signal may selectively result in focal Fz activation and asymmetric relocalization of Dsh to the membrane, where Dsh effects cytoskeletal reorganization to orient prehair initiation.
The segment polarity gene dishevelled (dsh) of Drosophila is required for pattern formation of the embryonic segments and the adult imaginal discs. dsh encodes the earliest-acting and most specific known component of the signal transduction pathway of Wingless, an extracellular signal homologous to Wnt1 in mice. We have previously described the isolation and characterization of the Dvl1 mouse dsh homolog. We report here the isolation of a second mouse dsh homolog, Dvl2, which maps to chromosome 11. The Dvl2 amino acid sequence is equally related to the dsh sequence as is that of Dvl1, but Dvl2 is most similar to the Xenopus homolog Xdsh. However, unlike the other vertebrate dsh homologs. Like the other genes, Dvl2 is ubiquitously expressed throughout most of embryogenesis and is expressed in many adult organs. We have developed an assay for dsh function in fly embryos, and show that Dvl2 can partially rescue the segmentation defects of embryos devoid of dsh. Thus, Dvl2 encodes a mammalian homolog of dsh which can transduce the Wingless signal.
In Drosophila, the Wingless and Notch signaling pathways function in m any of the same developmental patterning events. Genetic analysis demonstrates that the dishevelled gene, which encodes a molecule previously implicated in implementation of the Winglass signal, interacts antagonistically with Notch and one of its known ligands, Delta. A direct physical interaction between Dishevelled and the Notch carboxyl terminus, distal to the cdc10/ankyrin repeats, suggests a mechanism for this interaction. It is proposed that Dishevelled, in addition to transducing the Wingless signal, blocks Notch signaling directly, thus providing a molecular mechanism for the inhibitory cross talk observed between these pathways.
Signaling factors of the Wnt proto-oncogene family are implicated in dorsal axis formation during vertebrate development, but the molecular mechanism of this process is not known. Studies in Drosophila have indicated that the dishevelled gene product is required for wingless (Wnt1 homolog) signal transduction. We demonstrate that injection of mRNA encoding a Xenopus homolog of dishevelled (Xdsh) into prospective ventral mesodermal cells triggers a complete dorsal axis formation in Xenopus embryos. Lineage tracing experiments show that cells derived from the injected blastomere contribute to anterior and dorsal structures of the induced axis. In contrast to its effect on mesoderm, overexpression of Xdsh mRNA in prospective ectodermal cells triggers anterior neural tissue differentiation. These studies suggest that Wnt signal transduction pathway is conserved between Drosophila and vertebrates and point to a role for maternal Xdsh product in dorsal axis formation and in neural induction.
The Wnt genes encode conserved secreted proteins that play a role in normal development and tumorigenesis. Little is known about the signal transduction pathways of Wnt gene products. One of the best characterized Wnt family members is the Drosophila segment polarity gene wingless. We have investigated whether segment polarity genes with a wingless-like phenotype mediate the wingless signal. We used a wingless transgene controlled by a heat-shock promoter for genetic epistasis experiments. We show that wingless acts through dishevelled and armadillo to affect the expression of the homeobox gene engrailed and cuticle differentiation.
The Drosophila Wnt-1 homolog, wingless (wg), is involved in the signaling of patterning information in several contexts. In the embryonic epidermis, Wg protein is secreted and taken up by neighboring cells, in which it is required for maintenance of engrailed transcription and accumulation of Armadillo protein. The dishevelled (dsh) gene mediates these signaling events as well as wg-dependent induction across tissue layers in the embryonic midgut. dsh is also required for the development processes in which wg functions in adult development. Overall, cells lacking dsh are unable to adopt fates specified by Wg. dsh functions cell autonomously, indicating that it is involved in the response of target cells to the Wg signal. dsh is expressed uniformly in the embryo and encodes a novel protein with no known catalytic motifs, although it shares a domain of homology with several junction-associated proteins. Our results demonstrate that dsh encodes a specific component of Wg signaling and illustrate that Wnt proteins may utilize a novel mechanism of extracellular signal transduction.
In the Drosophila embryo dishevelled (dsh) function is required by target cells in order to respond to wingless (wg, the homolog of Wnt-1), demonstrating a role for dsh in Wnt signal transduction. We have isolated a mouse homolog of the Drosophila dsh segment polarity gene. The 695-amino-acid protein encoded by the mouse dishevelled gene (Dvl-1) shares 50% identity (65% similarity) with dsh. Similarity searches of protein and DNA data bases revealed that Dvl-1 encodes an otherwise novel polypeptide. While no functional motifs were identified, one region of Dvl-1 was found to be similar to a domain of discs large-1 (dlg), a Drosophila tumor suppressor gene. In the embryo, Dvl-1 is expressed in most tissues, with uniformly high levels in the central nervous system. From 7.5 days postcoitum Dvl-1 is expressed throughout the developing brain and spinal cord, including those regions expressing Wnt-1 and En. Expression of Dvl-1 in adult mice was found to be widespread, with brain and testis exhibiting the highest levels. The majority of Dvl-1 expression in the adult cerebellum is in the granular cell layer, similar to the pattern seen for engrailed-2 (En-2). Throughout postnatal development of the brain Dvl-1 is highly expressed in areas of high neuronal cell density.