The Wingless Signaling Pathway Is Directly Involved inDrosophilaHeart Development

AbstractHeart development in both vertebrates andDrosophilais initiated by bilaterally symmetrical primordia that may be of equivalent embryological origin: the anterior lateral plate mesoderm in vertebrates and the dorsal-most mesoderm in arthropods. These mesodermal progenitors then merge into a heart tube at the ventral midline (vertebrates) or the dorsal midline (Drosophila). These observations suggest that there may be similarities between vertebrate and invertebrate heart development. The homeobox gene,tinman,is required for heart as well as visceral mesoderm formation inDrosophila,and at least one of several vertebrate genes with similarities in protein sequence and cardiac expression totinmanis crucial for heart development in vertebrates. Inductive signals are also required forDrosophilaheart development: The secreted gene product ofwingless(wg) is critical for heart development during a time period distinct from its function in segmentation and neurogenesis. Here, we show thatwgis epistatic to hedgehog (hh), another secreted segmentation gene product, in its requirement for heart formation. We also provide evidence show that downstream ofwgin the signal transduction cascade,dishevelled(dsh,a pioneer protein) andarmadillo(arm, β-catenin homolog) are mediating the cardiogenic Wg signal. In particular, overexpression ofdshcan restore heart formation in the absence ofwgfunction. We discuss the possibility that Wg signaling is part of a combinatorial mechanism to specify the cardiac mesoderm