Dissecting The Effect Of Conditional Deletion Of Dnmt1 And Dnmt3a Specifically In Interneurons On Learning And Memory

The formation and consolidation of new memories involve a range of molecular and cellular changes,including gene transcription,protein synthesis,and dynamic changes of synaptic plasticity.Some of these changes are generated during the learning process and are maintained throughout lifetime.More and more evidences have indicated that epigenetic mechanisms play a critical role in the regulation of synaptic plasticity,the formation and consolidation of memory by regulating gene transcription.Epigenetic mechanisms include DNA covalent modification?DNA methylation,hydroxymethylation and demethylation?,histone post-translation modification,non-coding RNA regulation,chromatin remodeling,and so on.Among these epigenetic changes,DNA methylation is one of the most fully studied epigenetic modification forms.DNA methylation is critical for many biological processes,such as gene expression regulation,cell fate determination and disease development.DNA methylation is established via DNA methyltransferase?DNMT?enzymes which transfers methyl from s-adenosine methionine?SAM?to the 5th carbon of cytosine residue to form 5-methylcytosine?5mC?.DNMT1 has a high binding activity to hemimethylated DNA?one strand in the DNA double strand is methylated?and mainly serves to maintain methylation.However DNMT3a and DNMT3b cannot distinguish between unmethylated and hemimethylated substrates and thus play a major role in de novo methylation of DNA.The role of DNMTs in learning and memory has been studied mainly in glutamatergic excitatory neurons.However,numerous studies have shown that GABAergic inhibitory neurons also paly important role in brain function,including learning and memory.Therefore,in this study,we used genetic methods to selectively knock out Dnmt3a and Dnmt1 in GABAergic inhibitory neurons,to study the specific role of GABAergic Dnmt3a and Dnmt1in modulating learning and memory processes.We established conditional Dnmt3a and Dnmt1double knock-out?DKO?mice lines,including Dlx5/6-cre;Dnmt?3a,1?^2flox/2flox mice,Pv-cre;Dnmt?3a,1?^2flox/2flox mice and Sst-cre;Dnmt?3a,1?^2flox/2flox mice.Using a series of behavioral paradigms,such as the open field test?OF?,Elevated Plus Maze?EPM?,Rota-Rod,New Object Recognition?NOR?,Object-in-place recognition?NPR?and the Morris water maze,we compared the behavioral performance of these mice.Our results are listed as following:1.Effect of selective deletion of Dnmt3a and Dnmt1 in DLX5/6-expressing GABAergic inhibitory neurons on learning and memory.Dlx5/6-Cre;Dnmt?3a,1?^2flox/2flox mice showed motor learning deficit compared with their littermate control Dnmt?3a,1?^2flox/2flox mice in the Rota-Rod test.Dlx5/6-Cre;Dnmt?3a,1?^2flox/2flox mice showed normal spatial learning but impaired spatial memory.These mutant mice also showed normal object recognition and object-place recognition.2.Effect of selective deletion of Dnmt3a and Dnmt1 in PV⁺GABAergic neurons on learning and memory.Pv-Cre;Dnmt?3a,1?²flox/2floxflox/2flox mice showed normal basal anxiety and normal locomotor activity..Pv-cre;Dnmt?3a,1^?2flox/2flox2flox/2flox mice showed normal motor coordination and normal motor learning in Rota-Rod test.Pv-Cre;Dnmt?3a,1?²flox/2floxflox/2flox mice exhibited spatial memory deficits with intact spatial learning.3.Effects of selective deletion of Dnmt3a and Dnmt1 in Sst⁺GABAergic neurons on learning and memory.Sst-Cre;Dnmt?3a,1?²flox/2floxflox/2flox mice and their littermate control Dnmt3a,1^2flox/2flox mice displayed similar basal anxiety-related behavior and comparable spontaneous activity as tested in OF and EPM.Sst-Cre;Dnmt?3a,1?^2flox/2flox mice showed normal performance in motor coordination and motor learning.Sst-Cre;Dnmt?3a,1?^2flox/2flox mice exhibited similar spatial memory deficits as both Pv-cre;Dnmt?3a,1^?2flox/2flox2flox/2flox mice and Dlx5/6-Cre;Dnmt?3a,1?^2flox/2flox mice.In summary,we conclude that selective deletion of Dnmt3a and Dnmt1 in GABAergic neurons affects motor learning and spatial memory maintenance,while selective deletion of Dnmt3a and Dnmt1 in a subpopulation of PV⁺or Sst⁺interneurons primarily impairs long-term maintenance of spatial memory in mice.