Mechanism And Function Of Drosophila Neuroligin3 Proteolytic Cleavage

Neuroligins(Nlgs)are postsynaptic adhesion molecules that are essential for synaptic development and function.Mutations in Nlgs have been implicated in cognitive diseases such as autism.The functions of autism-associated Nlgs are modulated by their post-translational modifications,such as proteolytic cleavage of rodent Nlg1 by matrix metalloproteinase(MMP)-9/a disintegrin and metalloproteinase(ADAM)-10 to regulate neuronal activity and of Drosophila Nlg2(DNlg2),the latter of which is needed for its trafficking and maturation.A previous study has shown that there are different endogenous forms of DNlg3 in Drosophila heads,indicating it may undergo proteolytic processing.However,the molecular mechanism and function underlying DNlg3 proteolytic processing is unknown.In our present study,using a broad range of experimental methods including biochemistry,molecular biology,genetic studies and behavior analysis,we reveal a novel proteolytic mechanism that is essential for DNlg3 maturation and function in the central nervous system.DNlg3 undergoes proteolytic cleavage in the nervous system specifically.We identify that tumor necrosis factor a-converting enzyme(TACE)cleaves DNlg3 exclusively at its extracellular acetylcholinesterase-like domain(A520-N532)to generate the N-terminal fragment(NTF)and the short membrane-anchored fragment(sDNlg3).Interestingly,DNlg3 is constitutively processed in an activity-independent manner.Intriguingly,DNlg3 is cleaved intracellularly in the Golgi apparatus before it arrived at the cell surface,a unique cleavage mechanism that is distinct from 'conventional' ectodomain shedding of membrane proteins,including rodent Nlgl.Genetic studies show that sDNlg3 is essential for maintaining proper locomotor activity in Drosophila.In addition,ectopic sDNlg3 in muscles is functional which promotes GluRIIA recruitment at NMJ,suggesting that sDNlg3 is a mature form both in neurons and muscles.In summary,our results reveal a unique cleavage mechanism of DNlg3 and a neuron-specific role for DNlg3 maturation in the regulation of Drosophila behavior.Our study may provide a new insight into a cleavage mechanism of Nlgs maturation in the nervous system.