C.elegans MiR-83 Regulates The Function Of GABAergic Synapses By Inhibiting The Target UNC-52 Expression.

It has been reported that GABAergic synapses play important roles in the formation of neural products,construction of neural circuits,and development and function of mammalian nervous system.In mammals,more and more evidences show that anxiety and depression are due to the damage of GABA neurotransmitter in the early life.Moreover,the dysfunction of GABAergic neural circuits in cortex are related to various human neurodevelopmental disorders,including schizophrenia,autism and epilepsy.C.elegans is a good model to study neural development.It has been known that there are 302 neurons,and 2000 NMJs in the hermaphrodite worm.Although C.elegans nervous system is simpler than that in mammals,the genes of its nervous system are more homologous to them in mammals,including GABAergic synaptic genes.MicroRNAs(miRNAs)is a kind of small non-coding RNA,which are widespread found in recent years.They inhibit the target gene expressions by binding the 3'UTR of the target genes.Some evidences have showed that mi RNAs regulate the development of synapses at every stage,such as dendritic formation,synapse maturation and synapse development.But little is known that the function of miRNAs in GABAergic synapses.In our lab,we screened the mi RNAs involved in regulating the function of GABAegic synapses from the mi RNA mutant strains library,by the both PTZ(the GABA antagonists),and aldicarb(acetylcholinesterase inhibitors)hypersensitivity models.We found that mir-83 mutant worms are both sensitive to PTZ and aldicarb,suggesting that mir-83 is related to the function of GABAergic synapses.mir-29 is the mammalian homologs of mir-83.It is reported that mir-29 is related to the development and disorder of nervous system,and the neural cell death and apoptosis.Some results also showed that mir-29 is associated with the increased expression of Alzheimer's beta site lyse amyloid precursor protein 1(BACE1).In order to know the molecular mechanisms that mir-83 regulates the GABAergic synaptic function.We first identified unc-52 is one of the target genes of mir-83,by using bioinformatics methods,RT-PCR and luciferase analysis.Next,we constructed mir-83;unc-52 double mutants,and found the sensitivities to both PTZ and aldicarb in mir-83 mutant worms,were suppressed by unc-52 mutation.This suggested that mir-83 regulated GABAergic synaptic function by inhibiting its target gene unc-52 expression.Then,we can use specific markers of GABAA receptors unc-49::GFP in GABAergic postsynaptic membrane,and found that the density of GABAA receptors on postsynaptic membrane was decreased significantly in mir-83 mutant worms.This means that mir-83 regulates the distribution of GABAA receptor by suppressing unc-52 expression.In addition,the defects of axon growth in GABAergic motor neurons were found in mir-83 mutants,by the specific marker unc-47p::GFP.However,deletion of unc-52 did not restore this defect of mir-83 mutants.These results suggest that mir-83 can regulate the axon growth of GABAergic neurons,but not depending on its target gene unc-52.Our studies revealed the molecular mechanism of C.elegans mir-83 regulating the GABAergic synapses.These results built the base of studying mammalian miRNAs involved in regulating GABAergic synapses,and lead a new direction of studying the mechanism of neurological disease pathogenesis related to GABAergic synapses.