Genetic basis of thermal nociceptive sensitivity and brain weight in a BALB/c reduced complexity cross: BALB/cJ vs BALB/cByJ Spinal Cord RNAseq

We found BALB/cByJ mice showed enhanced sensitivity on the 53.5°C hot plate and mechanical stimulation in the von Frey test compared to BALB/cJ mice and replicated decreased gross brain weight in BALB/cByJ versus BALB/cJ. We then identified a quantitative trait locus (QTL) on chromosome 13 for hot plate sensitivity (LOD = 10.7; p < 0.001; peak = 56 Mb) and a QTL for brain weight on chromosome 5 (LOD = 8.7; p < 0.001). Expression QTL mapping of brain tissues identified H2afy (56.07 Mb) as the top transcript with the strongest association at the hot plate locus (FDR = 0.0002) and spliceome analysis identified differential exon usage within H2afy associated with the same locus. These data are spinal cord RNAseq to confirm differential expression of H2afy and other candidate genes. 16 Male and Female BALB/cJ vs BALB/cByJ (N=4/group) mice underwent pain testing at KUMC (PMID:35088629), were sacrificed, spinal cord tissues collected an preserved in RNAlater. RNA was extracted in RNAlater-preserved tissue using Trizol (Qiagen), ethanol precipitation, filtering columns (Qiagen), DNAse digestion (Qiagen), and elution with RNAse and nucleotide free water (Yazdani et al., 2015) and diluted to 100 ng/ul. RNA library preparation (poly-A selection) and RNA-seq were conducted at the University of Chicago Genomics Facility on an Illumina NovaSEQ6000 using a NovaSEQ SP-100 bp flowcell/reagent cassette. We used the R/Bioconductor package “scruff” to conduct demultiplexing, read alignment, read counting, quality checking and data visualization (Wang et al., 2019). Reads were trimmed for quality using Trimmomatic (Bolger et al., 2014). Trimmed reads were then aligned to the mm10 mouse reference genome (Ensembl) to generate BAM files for alignment using STAR (Dobin et al., 2013). For differential gene analysis in the spinal cord, the featureCounts read summarization program was used to count reads mapping to the “exon” feature in a GTF file obtained from Ensembl (GRCm38). Genes without 10 reads per million in at least 3 samples were excluded from analysis using EdgeR 51, and differential gene expression analysis of normalized counts was conducted using an appropriate design matrix, and reported using the topTable function.