title: Brain tumor regulates neuromuscular synapse growth and endocytosis in Drosophila by suppressing mad expression.
abstract: The precise regulation of synaptic growth is critical for the proper formation and plasticity of functional neural circuits. Identification and characterization of factors that regulate synaptic growth and function have been under intensive investigation. Here we report that brain tumor (brat), which was identified as a translational repressor in multiple biological processes, plays a crucial role at Drosophila neuromuscular junction (NMJ) synapses. Immunohistochemical analysis demonstrated that brat mutants exhibited synaptic overgrowth characterized by excess satellite boutons at NMJ terminals, whereas electron microscopy revealed increased synaptic vesicle size but reduced density at active zones compared with wild-types. Spontaneous miniature excitatory junctional potential amplitudes were larger and evoked quantal content was lower at brat mutant NMJs. In agreement with the morphological and physiological phenotypes, loss of Brat resulted in reduced FM1-43 uptake at the NMJ terminals, indicating that brat regulates synaptic endocytosis. Genetic analysis revealed that the actions of Brat at synapses are mediated through mothers against decapentaplegic (Mad), the signal transduction effector of the bone morphogenetic protein (BMP) signaling pathway. Furthermore, biochemical analyses showed upregulated levels of Mad protein but normal mRNA levels in the larval brains of brat mutants, suggesting that Brat suppresses Mad translation. Consistently, knockdown of brat by RNA interference in Drosophila S2 cells also increased Mad protein level. These results together reveal an important and previously unidentified role for Brat in synaptic development and endocytosis mediated by suppression of BMP signaling.
authors.affiliation: Key Laboratory of Molecular and Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China.
authors.forename: Wenwen
authors.initials: W
authors.lastname: Shi
authors.forename: Yan
authors.initials: Y
authors.lastname: Chen
authors.forename: Guangming
authors.initials: G
authors.lastname: Gan
authors.forename: Dan
authors.initials: D
authors.lastname: Wang
authors.forename: Jinqi
authors.initials: J
authors.lastname: Ren
authors.forename: Qifu
authors.initials: Q
authors.lastname: Wang
authors.forename: Zhiheng
authors.initials: Z
authors.lastname: Xu
authors.forename: Wei
authors.initials: W
authors.lastname: Xie
authors.forename: Yong Q
authors.initials: YQ
authors.lastname: Zhang
mesh_terms: D000818:Animals; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism*; D004331:Drosophila melanogaster; D004705:Endocytosis / Q000502:physiology*; D005260:Female; D005456:Fluorescent Dyes / Q000493:pharmacokinetics; D008297:Male; D008854:Microscopy, Electron; D016296:Mutagenesis; D009469:Neuromuscular Junction / Q000378:metabolism* / Q000648:ultrastructure; D009473:Neuronal Plasticity / Q000502:physiology*; D011726:Pyridinium Compounds / Q000493:pharmacokinetics; D000644:Quaternary Ammonium Compounds / Q000493:pharmacokinetics; D034741:RNA, Small Interfering / Q000235:genetics; D015398:Signal Transduction / Q000502:physiology; D013569:Synapses / Q000378:metabolism* / Q000648:ultrastructure; D013572:Synaptic Vesicles / Q000502:physiology / Q000648:ultrastructure; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
chemical_list: D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; C073804:FM1 43; D005456:Fluorescent Dyes; C112506:MAD protein, Drosophila; D011726:Pyridinium Compounds; D000644:Quaternary Ammonium Compounds; D034741:RNA, Small Interfering; D014157:Transcription Factors; C412783:brat protein, Drosophila