Impaired hippocampal NMDAR-LTP in a transgenic model of NSUN2-deficiency.

Biallelic loss-of-function NSUN2 mutations have recently been associated with cases of Autism Spectrum Condition (ASC), and NSun2-deficiency was also previously shown to cause a severe autosomal recessive intellectually disability disorder syndrome in which patients can sometimes display autistic behaviour. It has been demonstrated that NSUN2 can control protein synthesis rates via direct regulation of RNA methylation, and it is therefore of interest that other studies have suggested protein synthesis-dependent synaptic plasticity dysregulation as a mechanism for learning difficulties in various other autism-expressing conditions and disorders. Here we investigated NMDAR-LTP in a murine transgenic model harbouring loss-of-function mutation in the NSun2 gene and find an impairment of a protein synthesis-dependent form of this synaptic plasticity pathway. Our findings support the idea that NMDAR-LTP mis-regulation may represent a previously underappreciated mechanism associated with autism phenotypes.

Illustrating the Epitranscriptome at Nucleotide Resolution Using Methylation-iCLIP (miCLIP).

Next-generation sequencing technologies have enabled the transcriptome to be profiled at a previously unprecedented speed and depth. This yielded insights into fundamental transcriptomic processes such as gene transcription, RNA processing, and mRNA splicing. Immunoprecipitation-based transcriptomic methods such as individual nucleotide resolution crosslinking immunoprecipitation (iCLIP) have also allowed high-resolution analysis of the RNA interactions of a protein of interest, thus revealing new regulatory mechanisms. We and others have recently modified this method to profile RNA methylation, and we refer to this customized technique as methylation-iCLIP (miCLIP). Variants of miCLIP have been used to map the methyl-5-cytosine (m5C) or methyl-6-adenosine (m6A) modification at nucleotide resolution in the human transcriptome. Here we describe the m5C-miCLIP protocol, discuss how it yields the nucleotide-resolution RNA modification maps, and comment on how these have contributed to the new field of molecular genetics research coined "epitranscriptomics."