Unique genetic variation revealed by a microsatellite polymorphism survey in ten wild-derived inbred strains

Genetic analysis of the innate immune responses in wild-derived inbred strains of mice

The vertebrate immune system has evolved to recognize nucleic acids of bacterial and viral origin. Microbial DNA, as well as synthetic oligonucleotides based on these motifs, activates innate immune pathways mediated by the family of Toll-like receptors (TLR) initiating a cascade of signals in immune cells necessary for responses to pathogens. However, not all of the proteins that participate in TLR-mediated responses have been identified. In studies described herein, we observed significant variation in innate immune responses among selected wild-derived strains of mice. Specifically, we show that mice of MOLF/Ei, Czech/Ei, and MSM/Ms strains are hypo-responsive to polyinosinic-polycytidylic acid (poly(I:C)) because of a mutation in Tlr3. In addition, we discovered a hypo-response to cytosine guanine dinucleotide in MOLF/Ei mice and established that it is not linked to Tlr9, but to another locus. Further inquiry revealed that this hypo-response is transmitted as a monogenic dominant trait that can be mapped and cloned through positional cloning methods. These results suggest the existence of a novel molecule that can alter pro-inflammatory signals or activate additional signal transduction pathways. In addition, they support the wild-derived mouse strain as a forward genetic tool for the identification of novel immunological phenotypes.

Genetic control of parasite clearance leads to resistance to Plasmodium berghei ANKA infection and confers immunity

Unprecedented cure after infection with the lethal Plasmodium berghei ANKA was observed in an F2 progeny generated by intercrossing the wild-derived WLA and the laboratory C57BL/6 mouse strains. Resistant mice were able to clear parasitaemia and establish immunity. The observed resistance was disclosed as a combinatorial effect of genetic factors derived from the two parental strains. Genetic mapping of survival time showed that the WLA allele at a locus on chromosome 1 (colocalizing with Berghei resistance 1 (Berr1), a locus associated with resistance to experimental cerebral malaria) increases the probability to resist early death. Also, the C57Bl/6 allele at a novel locus on chromosome 9 (Berr3) confers overall resistance to this lethal Plasmodium infection. This report underlines the value of using wild-derived mouse strains to identify novel genetic factors in the aetiology of disease phenotypes, and provides a unique model for studying parasite clearance and immunity associated with malaria.

Efficient single nucleotide polymorphism discovery in laboratory rat strains using wild rat-derived SNP candidates

Background

The laboratory rat (Rattus norvegicus) is an important model for studying many aspects of human health and disease. Detailed knowledge on genetic variation between strains is important from a biomedical, particularly pharmacogenetic point of view and useful for marker selection for genetic cloning and association studies.

Results

We show that Single Nucleotide Polymorphisms (SNPs) in commonly used rat strains are surprisingly well represented in wild rat isolates. Shotgun sequencing of 814 Kbp in one wild rat resulted in the identification of 485 SNPs as compared with the Brown Norway genome sequence. Genotyping 36 commonly used inbred rat strains showed that 84% of these alleles are also polymorphic in a representative set of laboratory rat strains.

Conclusion

We postulate that shotgun sequencing in a wild rat sample and subsequent genotyping in multiple laboratory or domesticated strains rather than direct shotgun sequencing of multiple strains, could be the most efficient SNP discovery approach. For the rat, laboratory strains still harbor a large portion of the haplotypes present in wild isolates, suggesting a relatively recent common origin and supporting the idea that rat inbred strains, in contrast to mouse inbred strains, originate from a single species, R. norvegicus.

Identification of two cerebral malaria resistance loci using an inbred wild-derived mouse strain

Malaria is a complex infectious disease in which the host/parasite interaction is strongly influenced by host genetic factors. The consequences of plasmodial infections range from asymptomatic to severe complications like the neurological syndrome cerebral malaria induced by Plasmodium falciparum in humans and Plasmodium berghei ANKA in rodents. Mice infected with P. berghei ANKA show marked differences in disease manifestation and either die from experimental cerebral malaria (ECM) or from hemolytic anemia caused by hyperparasitemia (HP). A majority of laboratory mouse strains so far investigated are susceptible to ECM; however, a number of wild-derived inbred strains show resistance. To evaluate the genetic basis of this difference, we crossed a uniquely ECM-resistant, wild-derived inbred strain (WLA) with an ECM susceptible laboratory strain (C57BL/6J). All of the (WLA x C57BL/6J) F(1) and 97% of the F(2) progeny displayed ECM resistance similar to the WLA strain. To screen for loci contributing to ECM resistance, we analyzed a cohort of mice backcrossed to the C57BL/6J parental strain. A genome wide screening of this cohort provided significant linkage of ECM resistance to marker loci in two genetic regions on chromosome 1 (chi(2) = 18.98, P = 1.3 x 10(-5)) and on chromosome 11 (chi(2) = 16.51, P = 4.8 x 10(-5)), being designated Berr1 and Berr2, respectively. These data provide the first evidence of loci associated with resistance to murine cerebral malaria, which may have important implications for the search for genetic factors controlling cerebral malaria in humans.