Identification of genetic factors (QTL) of host susceptibility to organ specific bacterial infections in a highly genetically diverse reference mouse population, the Collaborative Cross

Dr. Fuad Iraqi

Infectious diseases are major constraints to human and livestock health world-wide. Current control mechanisms rely primarily on drugs and to a limited degree on vaccination. With the rise of antibiotic resistance in bacteria, there is a need for alternative, effective and affordable control methods. Understanding the nature of genetic susceptibility to bacterial infectious diseases will open new avenues for developing alternative control mechanisms. Here, our primary aim to identify the genetic factors (quantitative trait loci, QTL) that influence susceptibility to respiratory bacterial infectious diseases, which based on the World Health Organisation (WHO) are responsible for nearly half of bacterial infections worldwide, although other diseases will be included as controls. We anticipate finding specific genetic loci responsible for either resistance or susceptibility to infections by the respiratory pathogens. The identification of genetic information of such innate immune will help of understanding why certain hosts succumb to the infection while others do not. Subsequently, by exploiting the complete genome sequence data of the mouse and human, and using comparative mapping approaches, our aim is to identify host resistant/susceptible genes and their biological roles during bacterial infectious in humans. Our reference population and the focal point of the project will be a unique genetically highly diverse set of 180 recombinant inbred mouse lines (RIL) derived from crosses among 8 diverse founder inbred lines. These lines are the first cohort of the Collaborative Cross (CC) population which will eventually comprise 1600 RIL. These mouse RIL were specifically designed to provide a powerful resource for QTL mapping They exhibit about four-fold map expansion, increasing accuracy of QTL map location in proportion, and because of their inbred nature, all genetic contrasts involve homozygotes, thus increasing genetic variation associated with each QTL. In addition, multiple individuals can be phenotype! d in eac
h line reducing environmental sources of variation. In this way, the effective mapping power of the set of RIL is increased many-fold relative to standard F2 mapping populations. The lines will be genotyped with respect to 10,000 single nucleotide polymorphism (SNP) markers (using the commercially available10K mouse SNP chip). The set of RIL are also very cost effective with respect to genotyping costs, since the entire set of RIL need be typed only once, and the same genotyping data will apply to all mapping experiments. The RIL will be challenged by a set of pathogens, including; Klebsiella pneumonaie (colonizes upper respiratory system but causes disease in the lower respiratory system), Mycobacterium tuberculosis (strict lower respiratory pathogen), and Streptococcus pyogenes (upper respiratory infection). As these bacterial pathogens include gram negative and gram positive bacteria, we will also include specific components of these bacteria involved in septic shock namely, lipopolysaccharide (LPS) and (putative) lipoteichoic acid (LTA) for Gram- and Gram+, bacteria, respectively In order to ascertain the specificity of such genetic loci, we will include pathogens/toxins that colonize and cause disease in other sites and organs of the body, namely Shiga toxin for enteric diseases and Brucella melitensis as zoonotic disease colonizing the vaginal tract. Following challenge, the individual mice will be characterized for their response to infection and resistance/susceptibility according to the parameters appropriate for each pathogen or toxin. By use of multi-trait and multi-locus analytical methods that we propose to develop specifically for use in this genetically and phenotypically highly diverse reference population, we will be able to map QTL with unprecedented precision allowing the direct identification of potential candidate genes and their multi-locus epistatic interactions associated with susceptibility to infectious diseases.