GSE60262
Quantitative Analysis of Wild Type and Dicer1-ifKO Hippocampal Transcriptomes (mRNA and small RNA) Through Next Generation Sequencing (smallRNA-Seq).
Methods: CaMKIIa-creERT2 (Erdmann et al., 2007) and Dicer1f/f (Harfe et al., 2005) were crossed to produce inducible forebrain-restricted Dicer1 knockout mice (Dicer-ifKO) mice. Hippocampal small RNA profiles of 3-month-old wild-type (WT) and (Dicer-ifKO) mice were generated by deep sequencing, in triplicate, using Illumina HiSeq 2500. Each sample included total RNA isolated from the hippocampus of 3 mice. In total, 12 mice per genotype were used. After trimming of the adapter sequences and masking for low-complexity or low-quality sequence, the inserts were sorted in separated files according to their lengths. The reads in which no match of the adapter sequences is found were discarded. Inserts of length 18-50 were pooled together and mapped to reference genome (GRCm38/mm10) using Burrows-Wheeler Alignment Tool (BWA) v.0.5.9. We used BWA to map the inserts with a maximum of 2 mismatches. Inserts mapping to several positions on the reference sequences with the same mapping quality were attributed at random to one of the position with a mapping quality of 0. Files were further processed using Samtools v.0.1.18 to get binary files (BAM). Read count quantitations were obtained using Seqmonk (0.26.0). We counted reads that mapped to annotated features (miRNAs, 2035; miscRNA, 491; mRNA 76938; rRNA, 341; snoRNA, 1602; snRNA, 1431; tRNAs, 26248; tRNA, 22). The DESeq2 R package from Bioconductor was used to normalize the counts and perform the differential expression analysis. Results: We mapped about 17-22 million sequence reads per sample to the mouse genome (build GRCm38/mm10) and quantified 109,108 annotated features. DESeq2 R package was used to normalize the counts and perform the differential expression. Differential analysis output was filtered by FDR threshold (padj < 0.1). This approach led us to identify 119 annotated features (including 96 miRNAs) that were differentially regulated in the mouse hippocampus upon Dicer ablation. Conclusions: We extend here the characterization of inducible forebrain-restricted Dicer1 mutants confirming the initial memory improvement. Moreover, we describe several novel phenotypes associated with early Dicer loss in the mature brain including an exacerbated response to seizures, increased CA1 neuron excitability, a pronounced weight gain and enhanced induction of immediate early genes (IEGs) in relevant neuronal nuclei. To identify candidate genes that could explain these phenotypes, we conducted two complementary genomic screens for the miRNAs primarily affected and their targets. Overall, our results explain both the initial and late consequences of Dicer loss in excitatory neurons and indicate that Dicer and the miRNA system play a critical role regulating neuronal homeostasis and responsiveness. Overall design: Hippocampal small RNA profiles of 3-month-old wild-type (WT) and Dicer-ifKO (3 weeks upon tamoxifen administration) male mice were generated by deep sequencing, in triplicate, using Illumina HiSeq 2500. Each sample included total RNA isolated from the hippocampus of 3 mice. In total, 12 mice per genotype were used.