RESUMEN
Retrograde signaling plays an important role in synaptic homeostasis, growth, and plasticity. A retrograde signal at the neuromuscular junction (NMJ) of Drosophila controls the homeostasis of neurotransmitter release. Here, we show that this retrograde signal is regulated by the postsynaptic activity of Ca2+/calmodulin-dependent protein kinase II (CaMKII). Reducing CaMKII activity in muscles enhances the signal and increases neurotransmitter release, while constitutive activation of CaMKII in muscles inhibits the signal and decreases neurotransmitter release. Postsynaptic inhibition of CaMKII increases the number of presynaptic, vesicle-associated T bars at the active zones. Consistently, we show that glutamate receptor mutants also have a higher number of T bars; this increase is suppressed by postsynaptic activation of CaMKII. Furthermore, we demonstrate that presynaptic BMP receptor wishful thinking is required for the retrograde signal to function. Our results indicate that CaMKII plays a key role in the retrograde control of homeostasis of synaptic transmission at the NMJ of Drosophila.
Asunto(s)
Proteínas de Unión al Calcio , Proteínas Quinasas Dependientes de Calcio-Calmodulina/fisiología , Unión Neuromuscular/enzimología , Unión Neuromuscular/fisiología , Proteínas de Saccharomyces cerevisiae , Transmisión Sináptica/fisiología , Animales , Animales Modificados Genéticamente , Calcio/farmacología , Proteína Quinasa Tipo 2 Dependiente de Calcio Calmodulina , Proteínas Quinasas Dependientes de Calcio-Calmodulina/genética , Relación Dosis-Respuesta a Droga , Drosophila melanogaster , Electrofisiología , Potenciales Postsinápticos Excitadores/genética , Potenciales Postsinápticos Excitadores/fisiología , Regulación Enzimológica de la Expresión Génica , Genes de Insecto , Inmunohistoquímica , Manosiltransferasas/metabolismo , Manosiltransferasas/fisiología , Glicoproteínas de Membrana/metabolismo , Microscopía Electrónica , Músculos/metabolismo , Músculos/fisiología , Mutagénesis , Proteínas del Tejido Nervioso/metabolismo , Unión Neuromuscular/ultraestructura , Neuronas/metabolismo , Neuronas/fisiología , Neurotransmisores , Fragmentos de Péptidos/fisiología , Terminales Presinápticos/enzimología , Terminales Presinápticos/ultraestructura , Teoría Cuántica , Receptores AMPA/genética , Receptores AMPA/fisiología , SinaptotagminasRESUMEN
Highwire (Hiw), a putative RING finger E3 ubiquitin ligase, negatively regulates synaptic growth at the neuromuscular junction (NMJ) in Drosophila. hiw mutants have dramatically larger synaptic size and increased numbers of synaptic boutons. Here we show that Hiw binds to the Smad protein Medea (Med). Med is part of a presynaptic bone morphogenetic protein (BMP) signaling cascade consisting of three receptor subunits, Wit, Tkv, and Sax, in addition to the Smad transcription factor Mad. When compared to wild-type, mutants of BMP signaling components have smaller NMJ size, reduced neurotransmitter release, and aberrant synaptic ultrastructure. BMP signaling mutants suppress the excessive synaptic growth in hiw mutants. Activation of BMP signaling, which in wild-type does not cause additional growth, in hiw mutants does lead to further synaptic expansion. These results reveal a balance between positive BMP signaling and negative regulation by Highwire, governing the growth of neuromuscular synapses.
Asunto(s)
Proteínas Morfogenéticas Óseas/metabolismo , Diferenciación Celular/genética , Proteínas de Drosophila/metabolismo , Drosophila melanogaster/crecimiento & desarrollo , Proteínas del Tejido Nervioso/metabolismo , Unión Neuromuscular/crecimiento & desarrollo , Animales , Proteínas Morfogenéticas Óseas/genética , Tamaño de la Célula/genética , Proteínas de Unión al ADN/genética , Proteínas de Unión al ADN/metabolismo , Proteínas de Drosophila/genética , Drosophila melanogaster/metabolismo , Drosophila melanogaster/ultraestructura , Microscopía Electrónica , Neuronas Motoras/citología , Neuronas Motoras/metabolismo , Mutación/genética , Proteínas del Tejido Nervioso/genética , Unión Neuromuscular/metabolismo , Unión Neuromuscular/ultraestructura , Terminales Presinápticos/metabolismo , Terminales Presinápticos/patología , Terminales Presinápticos/ultraestructura , Unión Proteica/genética , Receptores de Superficie Celular/genética , Receptores de Superficie Celular/metabolismo , Receptores de Factores de Crecimiento Transformadores beta/genética , Receptores de Factores de Crecimiento Transformadores beta/metabolismo , Transducción de Señal/genética , Proteína Smad4 , Transmisión Sináptica/genética , Transactivadores/genética , Transactivadores/metabolismoRESUMEN
The synaptic adhesion molecules neurexin and neuroligin alter the development and function of synapses and are linked to autism in humans. Here, we found that Caenorhabditis elegans neurexin (NRX-1) and neuroligin (NLG-1) mediated a retrograde synaptic signal that inhibited neurotransmitter release at neuromuscular junctions. Retrograde signaling was induced in mutants lacking a muscle microRNA (miR-1) and was blocked in mutants lacking NLG-1 or NRX-1. Release was rapid and abbreviated when the retrograde signal was on, whereas release was slow and prolonged when retrograde signaling was blocked. The retrograde signal adjusted release kinetics by inhibiting exocytosis of synaptic vesicles (SVs) that are distal to the site of calcium entry. Inhibition of release was mediated by increased presynaptic levels of tomosyn, an inhibitor of SV fusion.