Drosophila neuromuscular synapse assembly and function require the TGF-β type I receptor saxophone and the transcription factor Mad

Transforming growth factor-βs (TGF-β) comprise a superfamily of secreted proteins with diverse functions in patterning and cell division control. TGF-β signaling has been implicated in synapse assembly and plasticity in both vertebrate and invertebrate systems. Recently, wishful thinking, a Drosophila gene that encodes a protein related to BMP type II receptors, has been shown to be required for the normal function and development of the neuromuscular junction (NMJ). These findings suggest that a TGF-β-related ligand activates a signaling cascade involving type I and II receptors and the Smad family of transcription factors to orchestrate the assembly of the NMJ. Here we demonstrate that the TGF-β type I receptor Saxophone and the downstream transcription factor Mothers against dpp (Mad) are essential for the normal structural and functional development of the Drosophila NMJ, a synapse that displays activity-dependent plasticity.