Orb2 as modulator of Brat and their role at the neuromuscular junction.

How synapses are built and dismantled is a central question in neurobiology. A wide range of proteins and processes from gene transcription to protein degradation are involved. Orb2 regulates mRNA translation depending on its monomeric or oligomeric state to modulate nervous system development and memory. Orb2 is expressed in Drosophila larval brain and neuromuscular junction (NMJ), Orb2 knockdown causes a reduction of synapse number and defects in neuronal morphology. Brain tumor (Brat) is an Orb2 target; it is expressed in larval brain related with cell growth and proliferation. Brat downregulation induces an increase in synapse number and abnormal growth of buttons and branches in neurons. In absence of Orb2, Brat is overexpressed suggesting that Orb2 is negatively regulating Brat mRNA translation. Orb2 or Brat control the expression of specific genes related to neuronal function. Orb2 is required for Liprin and Synaptobrevin transcription meanwhile Brat is required for Synaptobrevin and Synaptotagmin transcription. We present here evidences of a novel genetic mechanism to regulate synapse fine tuning during development and propose an equilibrium between Orb2 conformational state and nervous system formation.