ENU mutagenesis as a tool for understanding lung development and disease

Extensive Homeostatic T Cell Phenotypic Variation within the Collaborative Cross

The Collaborative Cross (CC) is a panel of reproducible recombinant inbred mouse strains with high levels of standing genetic variation, affording an unprecedented opportunity to perform experiments in a small animal model containing controlled genetic diversity while allowing for genetic replicates. Here, we advance the utility of this unique mouse resource for immunology research because it allows for both examination and genetic dissection of mechanisms behind adaptive immune states in mice with distinct and defined genetic makeups. This approach is based on quantitative trait locus mapping: identifying genetically variant genome regions associated with phenotypic variance in traits of interest. Furthermore, the CC can be utilized for mouse model development; distinct strains have unique immunophenotypes and immune properties, making them suitable for research on particular diseases and infections. Here, we describe variations in cellular immune phenotypes across F1 crosses of CC strains and reveal quantitative trait loci responsible for several immune phenotypes.

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The Collaborative Cross models the phenotypic diversity observed in human immunity

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QTL mapping in the CC reveals candidate genes linked to T cell phenotypes

Tinkering and the Origins of Heritable Anatomical Variation in Vertebrates

Evolutionary change comes from natural and other forms of selection acting on existing anatomical and physiological variants. While much is known about selection, little is known about the details of how genetic mutation leads to the range of heritable anatomical variants that are present within any population. This paper takes a systems-based view to explore how genomic mutation in vertebrate genomes works its way upwards, though changes to proteins, protein networks, and cell phenotypes to produce variants in anatomical detail. The evidence used in this approach mainly derives from analysing anatomical change in adult vertebrates and the protein networks that drive tissue formation in embryos. The former indicate which processes drive variation-these are mainly patterning, timing, and growth-and the latter their molecular basis. The paper then examines the effects of mutation and genetic drift on these processes, the nature of the resulting heritable phenotypic variation within a population, and the experimental evidence on the speed with which new variants can appear under selection. The discussion considers whether this speed is adequate to explain the observed rate of evolutionary change or whether other non-canonical, adaptive mechanisms of heritable mutation are needed. The evidence to hand suggests that they are not, for vertebrate evolution at least.

Manipulation of dipeptidylpeptidase 10 in mouse and human in vivo and in vitro models indicates a protective role in asthma

We previously identified dipeptidylpeptidase 10 (DPP10) on chromosome 2 as a human asthma susceptibility gene, through positional cloning. Initial association results were confirmed in many subsequent association studies but the functional role of DPP10 in asthma remains unclear. Using the MRC Harwell N-ethyl-N-nitrosourea (ENU) DNA archive, we identified a point mutation in Dpp10 that caused an amino acid change from valine to aspartic acid in the β-propeller region of the protein. Mice carrying this point mutation were recovered and a congenic line was established (Dpp10^145D). Macroscopic examination and lung histology revealed no significant differences between wild-type and Dpp10^145D/145D mice. However, after house dust mite (HDM) treatment, Dpp10 mutant mice showed significantly increased airway resistance in response to 100 mg/ml methacholine. Total serum IgE levels and bronchoalveolar lavage (BAL) eosinophil counts were significantly higher in homozygotes than in control mice after HDM treatment. DPP10 protein is present in airway epithelial cells and altered expression is observed in both tissue from asthmatic patients and in mice following HDM challenge. Moreover, knockdown of DPP10 in human airway epithelial cells results in altered cytokine responses. These results show that a Dpp10 point mutation leads to increased airway responsiveness following allergen challenge and provide biological evidence to support previous findings from human genetic studies.

This article has an associated First Person interview with the first author of the paper.

Summary: Here, we show a novel mouse model carrying a point mutation in dipeptidylpeptidase 10 (Dpp10). Our data provide evidence that DPP10 might play a protective role in asthma.

Functional analysis of a novel ENU-induced PHD finger 11 (Phf11) mouse mutant

Previously, human genetic studies have shown association between polymorphisms within the gene encoding plant homeodomain zinc finger protein 11 (PHF11) and asthma-related phenotypes. Initial functional studies have suggested that PHF11 may be involved in the immune response through regulation of T cell activities. In order to study further the gene’s functions, we have investigated the mouse Phf11 locus. We have established and characterised a mouse line harbouring a point mutation in the PHD domain of Phf11. Full-length mouse cDNA for Phf11 was obtained by applying rapid amplification of cDNA ends (RACE). All five exons encoding the PHD domain of Phf11 were directly sequenced in 3840 mouse DNA samples from the UK MRC Harwell ENU (N-ethyl-N-nitrosourea)-mutagenised DNA archive. Mice harbouring a valine to alanine substitution, predicted to have a significant functional impact on the PHD zinc finger domain, were re-derived. These Phf11 mutant mice were outcrossed to C3H mice and then backcrossed for ten generations in order to establish a congenic line harbouring the single point mutation in Phf11. Macroscopic examination, haematology and histological examination of lung structure revealed no significant differences between mutant and wild-type mice. After administration of lipopolysaccharide, the level of expression of Il2, NF-kB and Setdb2 were significantly increased in Phf11 mutant homozygous lungs compared to control littermates. Our results provide evidence that Phf11 can operate as a Th1 cell regulator in immune responses. Moreover, our data indicate that these mice may provide a useful model for future studies on Phf11.

A novel ENU-mutation in ankyrin-1 disrupts malaria parasite maturation in red blood cells of mice

The blood stage of the plasmodium parasite life cycle is responsible for the clinical symptoms of malaria. Epidemiological studies have identified coincidental malarial endemicity and multiple red blood cell (RBC) disorders. Many RBC disorders result from mutations in genes encoding cytoskeletal proteins and these are associated with increased protection against malarial infections. However the mechanisms underpinning these genetic, host responses remain obscure. We have performed an N-ethyl-N-nitrosourea (ENU) mutagenesis screen and have identified a novel dominant (haploinsufficient) mutation in the Ank-1 gene (Ank1^MRI23420) of mice displaying hereditary spherocytosis (HS). Female mice, heterozygous for the Ank-1 mutation showed increased survival to infection by Plasmodium chabaudi adami DS with a concomitant 30% decrease in parasitemia compared to wild-type, isogenic mice (wt). A comparative in vivo red cell invasion and parasite growth assay showed a RBC-autonomous effect characterised by decreased proportion of infected heterozygous RBCs. Within approximately 6–8 hours post-invasion, TUNEL staining of intraerythrocytic parasites, showed a significant increase in dead parasites in heterozygotes. This was especially notable at the ring and trophozoite stages in the blood of infected heterozygous mutant mice compared to wt (p<0.05). We conclude that increased malaria resistance due to ankyrin-1 deficiency is caused by the intraerythrocytic death of P. chabaudi parasites.

Genetic and genomic approaches to asthma: new insights for the origins

PURPOSE OF REVIEW

The aim is to update current understanding of the genes identified by the recent genome-wide association studies (GWASs) of asthma and its associated traits. The review also discusses how to dissect the functional roles of novel genes in future research.

RECENT FINDINGS

More than 10 GWAS aimed at identifying the genes underlying asthma and relevant traits have been published in the past 3 years. The largest of these was from the GABRIEL consortium, which discovered that the IL18R1, IL33, SMAD3, ORMDL3, HLA-DQ and IL2RB loci were all significantly associated with asthma. Many novel asthma genes, including those previously identified by positional cloning, are expressed within the respiratory epithelium, emphasizing the importance of epithelial barriers in causing asthma . The genes controlling IgE levels have surprisingly little overlap with the genes mediating asthma susceptibility, suggesting that atopy is secondary to asthma rather than a primary driver of the disease. The next challenge will be the systematic analysis of the precise functions of these genes in the pathogenesis of asthma.

SUMMARY

GWAS have uncovered many novel genes underlying asthma and detailed functional dissection of their roles in asthma will point the way to new therapies for the disease.

An ENU-mutagenesis screen in the mouse: identification of novel developmental gene functions

Background

Mutagenesis screens in the mouse have been proven useful for the identification of novel gene functions and generation of interesting mutant alleles. Here we describe a phenotype-based screen for recessive mutations affecting embryonic development.

Methodology/Principal Findings

Mice were mutagenized with N-ethyl-N-nitrosurea (ENU) and following incrossing the offspring, embryos were analyzed at embryonic day 10.5. Mutant phenotypes that arose in our screen include cardiac and nuchal edema, neural tube defects, situs inversus of the heart, posterior truncation and the absence of limbs and lungs. We isolated amongst others novel mutant alleles for Dll1, Ptprb, Plexin-B2, Fgf10, Wnt3a, Ncx1, Scrib(Scrib, Scribbled homolog [Drosophila]) and Sec24b. We found both nonsense alleles leading to severe protein truncations and mutants with single-amino acid substitutions that are informative at a molecular level. Novel findings include an ectopic neural tube in our Dll1 mutant and lung defects in the planar cell polarity mutants for Sec24b and Scrib.

Conclusions/Significance

Using a forward genetics approach, we have generated a number of novel mutant alleles that are linked to disturbed morphogenesis during development.

Pkd1l1 establishes left-right asymmetry and physically interacts with Pkd2

In mammals, left-right (L-R) asymmetry is established by posteriorly oriented cilia driving a leftwards laminar flow in the embryonic node, thereby activating asymmetric gene expression. The two-cilia hypothesis argues that immotile cilia detect and respond to this flow through a Pkd2-mediated mechanism; a putative sensory partner protein has, however, remained unidentified. We have identified the Pkd1-related locus Pkd1l1 as a crucial component of L-R patterning in mouse. Systematic comparison of Pkd1l1 and Pkd2 point mutants reveals strong phenocopying, evidenced by both morphological and molecular markers of sidedness; both mutants fail to activate asymmetric gene expression at the node or in the lateral plate and exhibit right isomerism of the lungs. Node and cilia morphology were normal in mutants and cilia demonstrated typical motility, consistent with Pkd1l1 and Pkd2 activity downstream of nodal flow. Cell biological analysis reveals that Pkd1l1 and Pkd2 localise to the cilium and biochemical experiments demonstrate that they can physically interact. Together with co-expression in the node, these data argue that Pkd1l1 is the elusive Pkd2 binding partner required for L-R patterning and support the two-cilia hypothesis.

Are there benefits from having two genetic fathers?

In this issue of Biology of Reproduction, Deng and colleagues present a method by which offspring originating from two male mouse genomes can efficiently be produced.