BMP Signaling
in Synapse Development
Retrograde BMP signaling
The neuromuscular junction is a synapse where motor neuron terminals communicate with muscle fibers to control movement, relying on signals to orchestrate its growth, maturation, maintenance, and function.
One of the key signals in Drosophila is retrograde bone morphogenetic protein (BMP) pathway signaling, which belongs to the Transforming Growth Factor- β (TGF-β) superfamily.
BMP ligands are secreted from muscle cells and motor neurons into the synaptic cleft, binding BMP receptors located on motor neuron terminals to activate the Smad transcription factors. Once activated, the Smad complex accumulates into motor neuron nuclei, binding to BMP-responsive DNA motifs embedded into enhancers and silencers to regulate gene expression. Without retrograde BMP signaling, the neuromuscular junction fails to grow properly and form mature synapses. In addition, neurotransmission and presynaptic plasticity, a property of synapses to compensate for neurotransmission loss, are also severely defective.
Understanding how this conserved signaling pathway orchestrates these diverse synaptic functions is highly valuable, offering critical insights into neuromuscular junction physiology and motor neuron diseases.
Our main questions
What genes are directly controlled by the BMP signaling pathway in motor neurons, and what are the molecular mechanisms that regulate them?
What are the functions of these genes at the neuromuscular junction, and how do they integrate with BMP signaling?
Which transcription factors collaborate with the activated Smads to regulate gene transcription in motor neurons?
Our approach and what we discovered
In our laboratory, we use the Drosophila neuromuscular junction as a model system, employing a multidisciplinary approach to explore these questions. We combine computational approaches with RNA-sequencing, gene reporter analysis, and advanced genome engineering techniques, such as CRISPR, to discover novel genes and enhancers. This comprehensive strategy allows us to elucidate the molecular mechanisms involved in BMP signaling at the neuromuscular junction.
Downstream Effector Genes
In this project, we aim to identify novel downstream effector genes in BMP signaling that influence the maturation and growth of synapses. To achieve this, we utilize an RNAseq approach to analyze differentially expressed genes in the Drosophila central nervous system (CNS) in BMP-deficient flies.
Our research has demonstrated that more than 600 genes are activated by BMP signaling in the fly ventral nerve cord, including 453 genes related to neurotransmission. We plan to further investigate the role of these genes in the maturation of the neuromuscular junction.
Our current focus is deciphering the role of the highly BMP-activated ly6 genes cluster, including a novel gene that we have named witty (without maturity), in neuromuscular junction maturation.
Transcription factors regulation in motor neurons
This project aims to identify transcription factors that convert the retrograde BMP signal into gene expression profiles to coordinate neuromuscular junction development, maturation and maintenance.
Using genome-wide RNA interference screens and transgenic reporter assays, we have discovered candidate transcription factors required for BMP target enhancer activation in motor neurons. We are currently characterizing how these transcription factors cooperate with the Smad transcription factors to regulate synaptic genes.
Retrograde BMP signaling
3rd instar Drosophila larva, muscle 4 NMJ. Red represent HRP staining and Cyne shows CSP.
BMP-dependent reporter expression in the ventral nerve cord. 3rd instar Drosophila larva, brain.
