Endocrine Regulation of Energy Balance by Drosophila TGF-β/Activins

The Transforming growth factor beta (TGF-beta) family of secreted proteins regulates a variety of key events in normal development and physiology. In mammals, this family, represented by 33 ligands, including TGF-beta, activins, nodal, bone morphogenetic proteins (BMPs), and growth and differentiation factors (GDFs), regulate biological processes as diverse as cell proliferation, differentiation, apoptosis, metabolism, homeostasis, immune response, wound repair, and endocrine functions. In Drosophila, only 7 members of this family are present, with 4 TGF-beta/BMP and 3 TGF-beta/activin ligands. Studies in the fly have illustrated the role of TGF-beta/BMP ligands during embryogenesis and organ patterning, while the TGF-beta/activin ligands have been implicated in the control of wing growth and neuronal functions. In this review, we focus on the emerging roles of Drosophila TGF-beta/activins in inter-organ communication via long-distance regulation, especially in systemic lipid and carbohydrate homeostasis, and discuss findings relevant to metabolic diseases in humans.