Dichotomous cis-regulatory motifs mediate the maturation of the neuromuscular junction by retrograde BMP signaling

Abstract

Retrograde bone morphogenetic protein (BMP) signaling at the Drosophila neuromuscular junction (NMJ) has served as a paradigm to study TGF-β-dependent synaptic function and maturation. Yet, how retrograde BMP signaling transcriptionally regulates these functions remains unresolved. Here, we uncover a gene network, enriched for neurotransmission-related genes, that is controlled by retrograde BMP signaling in motor neurons through two Smad-binding cis-regulatory motifs, the BMP-activating (BMP-AE) and silencer (BMP-SE) elements. Unpredictably, both motifs mediate direct gene activation, with no involvement of the BMP derepression pathway regulators Schnurri and Brinker. Genome editing of candidate BMP-SE and BMP-AE within the locus of the active zone gene bruchpilot, and a novel Ly6 gene witty, demonstrated the role of these motifs in upregulating genes required for the maturation of pre- and post-synaptic NMJ compartments. Our findings uncover how Smad-dependent transcriptional mechanisms specific to motor neurons directly orchestrate a gene network required for synaptic maturation by retrograde BMP signaling.

A genome engineered tool set forDrosophilaTGF-β/BMP signaling studies

“…All generated constructs were verified by sequencing. Some of the generated attP,KO as well as some reintegration lines were previously published: tkv [attP, KO] , Tkv-3xHA, pent [attP, KO] and YFP-Pent (Norman et al, 2016;Tracy Cai et al, 2019), Tkv-HAeGFP (Vigano et al, 2021), brk [attP, KO] , HA-Brk, shn [attP, KO] and Shn-HA (Vuilleumier et al, 2022), dally [attP, KO] , YFP-Dally, dlp [attP, KO] and HA-Dlp (Simon et al, 2024).…”