ABSTRACT: The molecular etiology of invididual differences in complex behavior traits and susceptibility to psychiatric illness remains incomplete. Using an unbiased genetic approach in a mouse model, Quantitative Trait Loci (QTL) influencing anxiety-like behaviors and beta-carboline-induced seizure vulnerability have been mapped to the distal portion of mouse chromosome 10 and an interval specific congenic strain (ISCS; A.B6chr10; 66 cM to telomere) was developed. This A.B6chr10 strain facilitated defining the behavioral influences of this region as well as gene expression profiling to identify candidate gene(s) underlying this QTL. By microarray studies, an unsuspected E3 Ubiquitin Ligase, Ring Finger 41 (Rnf41 / Neuregulin Receptor Degrading Protein1; Nrdp1) was differentially expressed in the region of interest, comparing the hippocampi of A/J vs A.B6chr10 mice as well as A/J vs B6 mice. By RT-PCR, Rnf41 expression levels were significantly increased 1.5 and 1.3-fold in the hippocampi of C57BL6/J and A.B6chr10 mice compared to A/J mice, respectively. In addition, protein levels of Rnf41 were increased in hippocampi of B6 mice compared to A/J mice across postnatal development with a 5.5-fold difference at P56. Among LxS recombinant inbred mice (N=33), Rnf41 hippocampal mRNA expression levels were significantly correlated with open field behavior (r= .454, p=.0073). Re-analyzing a microarray database of human post-mortem prefrontal cortex (Brodmannâ??s Area 46/10), RNF41 mRNA expression levels were reduced significantly in patients with major depression and bipolar disorder compared to unaffected controls. Overall, Rnf41 is a pleiotropic candidate gene for anxiety-like behaviors, depression, and vulnerability to seizures. RNF41 and its binding partners provide novel etiological pathways for influencing behavior, highlighting a potential role for the ubiquitin proteasome system in psychiatric illness. Keywords: strain difference, genetic variation Microarray Affymetrix GeneChip: From three independent pools (3 hippocampi /pool) of total RNA for each line, probe was labeled, hybridized as one pool per GeneChip, using a total of six mouse MOE 430 arrays (Affymetrix, Santa Clara, CA). The sequential steps of reverse transcriptions, purification of ds cDNA, in vitro transcription and labeling of cRNA with biotin (Enzo BioArray High Yield RNA Transcript Labeling Kit), fragmentation of cRNA, hybridization to gene chips in a Affymetrix fluidics station 400 system, staining with streptavidin-phycoerythrin, washings, and scannings with a GeneArray Scanner were performed as described in the detailed protocols of the Affymetrix GeneChip Expression Analysis Technical Manual (Affymetrix, Santa Clara, CA) by the UTSW Microarray Core. The Affymetrix two GeneChip MOE 430 A and B set contains more than 45,000 probe sets, interrogating the expression level of 34,000 mouse gene transcripts. Illumina Microarray For the P0.5 microarray study, total RNA from a whole brain was individually used per Sentrix Mouse-6 BeadChip (Illumina, San Diego, CA), allowing individual samples to be evaluated and an increased sample size, namely six P0.5 mouse brains for each of three lines (A/J, B6, A.B6chr10). The Sentrix Mouse-6 BeadChip contains total 47,769 gene-specific, 70-mer oligonucleotide probes. Total RNA from each brain tissue of P0.5 mice was extracted in Trizol as above, reverse transcribed, labeled, and hybridized with a microarray according to the manufacturerâ??s detailed protocol (Illumina, San Diego, Ca.). Briefly, total RNA was reverse transcribed, then in vitro transcribed to cRNA and labeled with biotin-16-UTP. The labeled probe was hybridized to Illumina's Sentrix mouse-6 Expression BeadChips (Illumina, San Diego, CA), washed, and scanned with Illumina's BeadStation 500GX Genetic Analysis System in the UTSW Microarray core.
