On the trail of anxiety

Abstract

With the advances in genome wide screening arrays and sequencing techniques scientists were enabled to examine genetic variations and their effects on behavioral phenotypes. While single nucleotide polymorphisms (SNPs) are the most widely studied form of genomic variations to date, another type of variants has become increasingly important in recent research, the copy number variants (CNVs). These large segments of DNA that can comprise up to several megabasepairs and differ in copy number with respect to a reference genome have been associated with several disorders and behavioral phenotypes before. This study investigated the influence of CNVs on anxiety related behavior. The detection of these variants turned out to be a major challenge since all methods available are biased by limitations of the design of the approach and the subsequent computational analyses. Therefore, three different techniques (next generation sequencing and two distinct whole genome genotyping arrays) were employed to identify CNVs in a CD 1 derived mouse model consisting of two mouse strains showing high (HAB) and low (LAB) anxiety related behavior, respectively. By comparing CNVs in HAB vs. LAB mice with expression data of four distinct brain regions of high relevance to the limbic system (central and basolateral amygdala, cingulate cortex and the hypothalamic paraventricular nucleus), it was shown that CNVs can influence the expression of protein coding genes by the alteration of the genes’ copy number per se. Therefore, the genes mapping into regions where CNVs were detected in HAB vs. LAB mice (by all three detection methods) were suggested to be possible effectors of anxiety related behavior. Amongst these candidate genes those were considered to be the most interesting ones that were additionally found to map into regions of CNVs associated with anxiety related behavior in CD 1 mice. CNVs in these mice were detected by means of a whole genome genotyping array and subsequent processing of the raw data with a novel computational approach that was adapted from existing analysis methods. Furthermore, to test the effect of a specific CNV on anxiety related behavior in vivo, a breeding approach was used to generate animals with a full genetic background of HAB mice except for one LAB derived locus harboring a CNV that included the Glo1 gene. No direct effect on the phenotype could be observed, however, the respective CNV might be involved in the manipulation of anxiety related behavior taken into account the interaction with other factors. Taken together, this study provides not only a comprehensive catalogue of CNVs in HAB/LAB mice but also the evidence that these variants can influence anxiety related behavior. Furthermore, it gives a first insight into the functionality of CNVs with respect to anxiety related behavior. Therefore, this thesis provides a profound basis for multiple advanced studies