The expression of Delta ligands in the sponge Amphimedon queenslandica suggests an ancient role for Notch signaling in metazoan development

In the present report we analyze the structure of the five A. queenslandica Deltas using bioinformatic methods, and characterize their developmental expression via whole mount in situ hybridization and histological staining.Sequence analysis of the A. queenslandica Delta ligands highlights the conservation of their extracellular domains. This contrasts with the divergence of their intracellular regions, each of which is predicted to bear a unique repertoire of protein interaction motifs. In keeping with this diversity, these ligands are expressed differentially and dynamically throughout A. queenslandica embryogenesis, both in cell type specific patterns and broader regional domains. Notably, this expression coincides with the development of the photosensitive larval pigment ring, the non-ciliated cuboidal cells located at the anterior pole of the larva, and the intraepithelial flask cells and globular cells that are presumed to have sensory and/or secretory roles.Based on the dynamic and complex patterns of expression of these Delta ligands and the Notch receptor, we propose that the Notch signaling pathway is involved in regulating the development of diverse cell types in A. queenslandica. From these observations we infer that Notch signaling is a conserved feature of metazoan development, ancestrally contributing to cell determination, patterning and differentiation processes.Intercellular signaling pathways drive animal development by facilitating cellular communication and the coordination of morphogenetic processes. Of the major developmental signaling pathways, comparative studies have revealed that core components of the Wnt, Notch, transforming growth factor β (TGFβ) and receptor tyrosine kinase (RTK) pathways are encoded in the genomes of representative species from all major extant animal clades [1,2]. Here, we focus on the evolution of one of these pathways, the Notch signaling pathway, which provides a mechanism for short-range, localized signaling betw