Strain-specific Modifiers Research Articles

Inbred SJL mice recapitulate human resistance to Cryptococcus infection due to differential immune activation.

Cryptococcosis studies often utilize the common C57BL/6J mouse model. Unfortunately, infection in these mice fails to replicate the basic course of human disease, particularly hampering immunological studies. This work demonstrates that SJL/J mice can recapitulate human infection better than other mouse strains. The immunological response to Cryptococcus infection in SJL/J mice was markedly different from C57BL/6J and much more productive in combating this infection. Characterization of infected mice demonstrated strain-specific genetic linkage and differential regulation of multiple important immune-relevant genes in response to Cryptococcus infection. While our results validate many of the previously identified immunological features of cryptococcosis, we also demonstrate limitations from previous mouse models as they may be less translatable to human disease. We concluded that SJL/J mice more faithfully recapitulate human cryptococcosis serving as an exciting new animal model for immunological and genetic studies.

Genetic background modifies phenotypic severity and longevity in a mouse model of Niemann-Pick disease type C1.

ABSTRACTNiemann-Pick disease type C1 (NPC1) is a rare, fatal neurodegenerative disorder characterized by lysosomal accumulation of unesterified cholesterol and glycosphingolipids. These subcellular pathologies lead to phenotypes of hepatosplenomegaly, neurological degeneration and premature death. NPC1 is extremely heterogeneous in the timing of clinical presentation and is associated with a wide spectrum of causative NPC1 mutations. To study the genetic architecture of NPC1, we have generated a new NPC1 mouse model, Npc1em1Pav. Npc1em1Pav/em1Pav mutants showed notably reduced NPC1 protein compared to controls and displayed the pathological and biochemical hallmarks of NPC1. Interestingly, Npc1em1Pav/em1Pav mutants on a C57BL/6J genetic background showed more severe visceral pathology and a significantly shorter lifespan compared to Npc1em1Pav/em1Pav mutants on a BALB/cJ background, suggesting that strain-specific modifiers contribute to disease severity and survival. QTL analysis for lifespan of 202 backcross N2 mutants on a mixed C57BL/6J and BALB/cJ background detected significant linkage to markers on chromosomes 1 and 7. The discovery of these modifier regions demonstrates that mouse models are powerful tools for analyzing the genetics underlying rare human diseases, which can be used to improve understanding of the variability in NPC1 phenotypes and advance options for patient diagnosis and therapy.This article has an associated First Person interview with the first author of the paper.

Congenic Mice Confirm That Collagen X Is Required for Proper Hematopoietic Development

The link between endochondral skeletal development and hematopoiesis in the marrow was established in the collagen X transgenic (Tg) and null (KO) mice. Disrupted function of collagen X, a major hypertrophic cartilage matrix protein, resulted in skeletal and hematopoietic defects in endochondrally derived tissues. Manifestation of the disease phenotype was variable, ranging from perinatal lethality in a subset of mice, to altered lymphopoiesis and impaired immunity in the surviving mice. To exclude contribution of strain specific modifiers to this variable manifestation of the skeleto-hematopoietic phenotype, C57Bl/6 and DBA/2J collagen X congenic lines were established. Comparable disease manifestations confirmed that the skeleto-hematopoietic alterations are an inherent outcome of disrupted collagen X function. Further, colony forming cell assays, complete blood count analysis, serum antibody ELISA, and organ outgrowth studies established altered lymphopoiesis in all collagen X Tg and KO mice and implicated opportunistic infection as a contributor to the severe disease phenotype. These data support a model where endochondral ossification-specific collagen X contributes to the establishment of a hematopoietic niche at the chondro-osseous junction.

Sox7 and Sox17 are strain-specific modifiers of the lymphangiogenic defects caused by Sox18 dysfunction in mice

Developmental defects caused by targeted gene inactivation in mice are commonly subject to strain-specific modifiers that modulate the severity of the phenotype. Although several genetic modifier loci have been mapped in mice, the gene(s) residing at these loci are mostly unidentified, and the molecular mechanisms of modifier action remain poorly understood. Mutations in Sox18 cause a variable phenotype in the human congenital syndrome hypotrichosis-lymphedema-telangiectasia, and the phenotype of Sox18-null mice varies from essentially normal to completely devoid of lymphatic vasculature and lethal, depending on the strain of the mice, suggesting a crucial role for strain-specific modifiers in this system. Here we show that two closely related Group F Sox factors, SOX7 and SOX17, are able to functionally substitute for SOX18 in vitro and in vivo. SOX7 and SOX17 are not normally expressed during lymphatic development, excluding a conventional redundancy mechanism. Instead, these genes are activated specifically in the absence of SOX18 function, and only in certain strains. Our studies identify Sox7 and Sox17 as modifiers of the Sox18 mutant phenotype, and reveal their mechanism of action as a novel mode of strain-specific compensatory upregulation.

Cumulative ligand activity of NODAL mutations and modifiers are linked to human heart defects and holoprosencephaly

The cyclopic and laterality phenotypes in model organisms linked to disturbances in the generation or propagation of Nodal-like signals are potential examples of similar impairments resulting in birth defects in humans. However, the types of gene mutation(s) and their pathogenetic combinations in humans are poorly understood. Here we describe a mutational analysis of the human NODAL gene in a large panel of patients with phenotypes compatible with diminished NODAL ligand function. Significant reductions in the biological activity of NODAL alleles are detected among patients with congenital heart defects (CHD), laterality anomalies ( e.g. left–right mis-specification phenotypes), and only rarely holoprosencephaly (HPE). While many of these NODAL variants are typical for family-specific mutations, we also report the presence of alleles with significantly reduced activity among common population variants. We propose that some of these common variants act as modifiers and contribute to the ultimate phenotypic outcome in these patients; furthermore, we draw parallels with strain-specific modifiers in model organisms to bolster this interpretation.

Expression of Jak2V617F causes a polycythemia vera–like disease with associated myelofibrosis in a murine bone marrow transplant model

AbstractAn acquired somatic mutation, Jak2V617F, was recently discovered in most patients with polycythemia vera (PV), chronic idiopathic myelofibrosis (CIMF), and essential thrombocythemia (ET). To investigate the role of this mutation in vivo, we transplanted bone marrow (BM) transduced with a retrovirus expressing either Jak2 wild-type (wt) or Jak2V617F into lethally irradiated syngeneic recipient mice. Expression of Jak2V617F, but not Jak2wt, resulted in clinicopathologic features that closely resembled PV in humans. These included striking elevation in hemoglobin level/hematocrit, leukocytosis, megakaryocyte hyperplasia, extramedullary hematopoiesis resulting in splenomegaly, and reticulin fibrosis in the bone marrow. Histopathologic and flow cytometric analyses showed an increase in maturing myeloid lineage progenitors, although megakaryocytes showed decreased polyploidization and staining for acetylcholinesterase. In vitro analysis of primary cells showed constitutive activation of Stat5 and cytokine-independent growth of erythroid colony-forming unit (CFU-E) and erythropoietin hypersensitivity, and Southern blot analysis for retroviral integration indicated that the disease was oligoclonal. Furthermore, we observed strain-specific differences in phenotype, with Balb/c mice demonstrating markedly elevated leukocyte counts, splenomegaly, and reticulin fibrosis compared with C57Bl/6 mice. We conclude that Jak2V617F expression in bone marrow progenitors results in a PV-like syndrome with myelofibrosis and that there are strain-specific modifiers that may in part explain phenotypic pleiotropy of Jak2V617F-associated myeloproliferative disease in humans.

Haploinsufficient Bmp4 ocular phenotypes include anterior segment dysgenesis with elevated intraocular pressure

BackgroundGlaucoma is a blinding disease usually associated with high intraocular pressure (IOP). In some families, abnormal anterior segment development contributes to glaucoma. The genes causing anterior segment dysgenesis and glaucoma in most of these families are not identified and the affected developmental processes are poorly understood. Bone morphogenetic proteins (BMPs) participate in various developmental processes. We tested the importance of Bmp4 gene dosage for ocular development and developmental glaucoma.ResultsBmp4+/- mice have anterior segment abnormalities including malformed, absent or blocked trabecular meshwork and Schlemm's canal drainage structures. Mice with severe drainage structure abnormalities, over 80% or more of their angle's extent, have elevated IOP. The penetrance and severity of abnormalities is strongly influenced by genetic background, being most severe on the C57BL/6J background and absent on some other backgrounds. On the C57BL/6J background there is also persistence of the hyaloid vasculature, diminished numbers of inner retinal cells, and absence of the optic nerve.ConclusionsWe demonstrate that heterozygous deficiency of BMP4 results in anterior segment dysgenesis and elevated IOP. The abnormalities are similar to those in human patients with developmental glaucoma. Thus, BMP4 is a strong candidate to contribute to Axenfeld-Rieger anomaly and other developmental conditions associated with human glaucoma. BMP4 also participates in posterior segment development and wild-type levels are usually critical for optic nerve development on the C57BL/6J background. Bmp4+/- mice are useful for studying various components of ocular development, and may allow identification of strain specific modifiers affecting a variety of ocular phenotypes.

Mutations in mouse Aristaless-like4 cause Strong's luxoid polydactyly.

Mutations that affect vertebrate limb development provide insight into pattern formation, evolutionary biology and human birth defects. Patterning of the limb axes depends on several interacting signaling centers; one of these, the zone of polarizing activity (ZPA), comprises a group of mesenchymal cells along the posterior aspect of the limb bud that express sonic hedgehog (Shh) and plays a key role in patterning the anterior-posterior (AP) axis. The mechanisms by which the ZPA and Shh expression are confined to the posterior aspect of the limb bud mesenchyme are not well understood. The polydactylous mouse mutant Strong's luxoid (lst) exhibits an ectopic anterior ZPA and expression of Shh that results in the formation of extra anterior digits. Here we describe a new chlorambucil-induced deletion allele, lstAlb, that uncovers the lst locus. Integration of the lst genetic and physical maps suggested the mouse Aristaless-like4 (Alx4) gene, which encodes a paired-type homeodomain protein that plays a role in limb patterning, as a strong molecular candidate for the Strong's luxoid gene. In genetic crosses, the three lst mutant alleles fail to complement an Alx4 gene-targeted allele. Molecular and biochemical characterization of the three lst alleles reveal mutations of the Alx4 gene that result in loss of function. Alx4 haploinsufficiency and the importance of strain-specific modifiers leading to polydactyly are indicative of a critical threshold requirement for Alx4 in a genetic program operating to restrict polarizing activity and Shh expression in the anterior mesenchyme of the limb bud, and suggest that mutations in Alx4 may also underlie human polydactyly.

Control of expression and methylation of a hepatitis B virus transgene by strain-specific modifiers.

In transgenic animals, genotype-specific modifiers exert a control over transgene methylation and expression that may or may not be position dependent. These factors belong to different classes, some of them possibly related to modifiers of position-effect variegation in Drosophila. The study of hepatitis B virus (HBV) gene expression in transgenic mice has revealed the existence of many factors influencing transcription, including hormones and tissue-specific transcription factors. We now report the effect of genotype-specific modifiers on HBV surface antigen (HBsAg) expression and transgene methylation. Compared with the C57BL/6 background, the DBA/2 and 129sv backgrounds cause enhancement of HBsAg expression, with little or not effect on transgene methylation or transcription. In contrast, a single cross with a BALB/c mouse is responsible for de novo methylation and silencing of the transgene in all offspring. Several modifiers appear to segregate in the progeny of a transgenic E36 male mouse crossed with (C57BL/6 x BALB/c) F1 females, with the emergence of a high-expressor group. Our observations suggest that different modifiers act cooperatively, at both the transcriptional and post-transcriptional levels, as part of a complex system regulating transgene expression. This transgenic model provides a system to genetically map new mouse strain-specific modifiers, some of them involved in epigenetic modification and transcription control.

Quantitative control of gene expression by nucleocytoplasmic interactions in early mouse embryos: consequence for reprogrammation by nuclear transfer.

HSP 70.1 is one of the first genes to be expressed in the mouse embryo at the time of zygotic genome activation. We studied the regulation of this gene, using a transgene associating HSP 70.1 promoter and the firefly luciferase reporter gene, which allows the precise quantification of HSP 70.1 level of expression on individual embryos. In the present work, we show first that the level of HSP 70.1 expression at the two-cell stage is significantly higher (around two-fold) in embryos whose maternal cytoplasm is from C3H strain than with BALB/c strain. We verified that this difference is not an artefact of the use of transgenic embryos, of the time of first cleavage, or of in vitro culture. This regulation of HSP 70.1 level of expression is controlled by strain-specific maternal modifiers and is independent of replication, syngamy, and mitosis. Following nuclear transfer, reactivation of HSP 70.1 is also subjected to the same epigenetic influence. Only the strain-of-origin of the recipient cytoplast modulates the level of HSP 70.1 reprogrammation; the origin of donor nucleus is not significant, demonstrating the reversibility of this strain effect. These results point out the importance of the quality of recipient cytoplast in the intensity of gene reprogrammation, which may be of importance for nuclear transfer efficiency.

Genomic imprinting: Lessons from mouse transgenes

Genomic imprinting is a non-Mendelian form of inheritance that results in an expression difference between the two parental alleles of an autosomal locus. The study of mouse transgenes has providede us with descriptions of a variety of imprinting or parent-of-origin effects, thereby anticipating similar inheritance phenomena in non-transgenic mice. Many mouse transgenes exhibit parent-of-origin behavior only on mixed strain backgrounds, whereas others are imprinted on inbred strain backgrounds. In the former cases, the parent-of-origin effects are due to strain-specific modifiers of DNA methylation and expression. These are inherited in a parent-specific fashion and exert their effects after fertilization. In the latter cases, true germline transgene imprinting, the creation of an imprinted locus occurs in a series of sequential steps. First, there is an erasure of the imprint from the previous generation in both male and female fetal germ cells. Second, upon completion of gametogenesis, distinctive methylation patterns have been placed on the transgens sequences of the two mature gametes. Third, only one of these inherited patterns is maintained in the early, pre-implantation embryo. The pattern of the other parental allele is erased. Finally, the methylation pattern of the alleles evolve in the later stages of development, but nonetheless the methylation difference (imprint) of the locus persists. Transgene imprinting behaviors, either on mixed strain backgrounds and on inbred genetic backgrounds, have counterparts in endogenous genetic phenomena.