17 TGF-β Family Signaling in Drosophila

In this chapter, we first introduce the general components of the different transforming growth factor-β (TGF-β) family signaling pathways that have been identified in Drosophila . We then describe at which steps and how the signaling pathways are regulated at different developmental stages. We highlight two topics—extracellular ligand distribution and nuclear readout of distinct levels of signaling—in which Drosophila work has provided unique insight in the past decade. For several reviews that discuss other aspects of TGF-β family signaling in Drosophila in more detail, see Affolter et al. (2001), Parker et al. (2004), and Raftery and Sutherland (1999). CORE EFFECTORS OF THE TGF-β FAMILY SIGNALING PATHWAYS IN DROSOPHILA The core components of TGF-β family signaling pathways in Drosophila show a high degree of conservation at the sequence as well as at the functional level with regard to their vertebrate counterparts, that is, the bone morphogenetic protein- (BMP) and activin-signaling pathways. In fact, several genes encoding Drosophila TGF-β family ligands or receptors were identified using polymerase chain reaction (PCR) approaches or by DNA sequence data mining starting from the sequences for mammalian members of the signaling pathway. The number of ligands and receptors encoded by the Drosophila genome is lower than that in vertebrates; seven ligand and five receptor-encoding genes have been identified (Fig. 1) (Parker et al. 2004). Three of the seven ligands, Decapentaplegic (Dpp), Screw (Scw), and Glass bottom boat (Gbb; formerly termed 60A), belong to the subfamily of BMPs, whereas dActivin and Dawdle (Daw) are related to...