[Show abstract][Hide abstract] ABSTRACT: Vertebrate organs show consistent left-right (L-R) asymmetry in placement and patterning. To identify genes involved in this process we performed an ENU-based genetic screen. Of 135 lines analyzed 11 showed clear single gene defects affecting L-R patterning, including 3 new alleles of known L-R genes and mutants in novel L-R loci. We identified six lines (termed "gasping") that, in addition to abnormal L-R patterning and associated cardiovascular defects, had complex phenotypes including pulmonary agenesis, exencephaly, polydactyly, ocular and craniofacial malformations. These complex abnormalities are present in certain human disease syndromes (e.g., HYLS, SRPS, VACTERL). Gasping embryos also show defects in ciliogenesis, suggesting a role for cilia in these human congenital malformation syndromes. Our results indicate that genes controlling ciliogenesis and left-right asymmetry have, in addition to their known roles in cardiac patterning, major and unexpected roles in pulmonary, craniofacial, ocular and limb development with implications for human congenital malformation syndromes.
[Show abstract][Hide abstract] ABSTRACT: N'-ethyl-N'-nitrosourea (ENU) is a powerful germline mutagen used in conjunction with phenotype-driven screens to generate novel mouse mutants. ENU also induces genetic lesions in somatic cells and dosage requires optimization between maximum germline mutation rate versus induced sterility and tumourigenesis that compromise the welfare and fecundity of the ENU-treated males. Here, we present our experience with BALB/cAnNCrl and C57BL/6J mice in terms of the pathology induced by ENU and its impact on breeding. In both mouse strains, morbidity and mortality rises with ENU dose. In more than 75% of C57BL/6J males, morbidity and mortality were attributable to the development of malignant T-lymphoblastic lymphoma. Approximately 50% of ENU-treated BALB/cAnNCrl males develop early malignant T-lymphoblastic lymphoma, but the cohort that survives develops late-onset lung carcinoma. Within strains, the latency of these clinically important tumour(s) was not dosage-dependent, but the proportion of mice developing tumours and consequently removed from the breeding programme increased with ENU dosage. The median number of offspring per ENU-treated C57BL/6J male in standard matings with C3H/HeH females decreased with increasing dosage. The two most important underlying causes for lower male fecundity were increased infertility in the highest dosage group and reduced numbers of litters born to the remaining fertile C57BL/6J males due to a higher incidence of morbidity. These findings have allowed us to refine breeding strategy. To maximize the number of offspring from each ENU-treated male, we now rotate productive males between two cages to expose them to more females. This optimizes the number of mutation carrying offspring while reducing the number of ENU-treated males that must be generated.
[Show abstract][Hide abstract] ABSTRACT: The development of the mammalian brain is dependent on extensive neuronal migration. Mutations in mice and humans that affect neuronal migration result in abnormal lamination of brain structures with associated behavioral deficits. Here, we report the identification of a hyperactive N-ethyl-N-nitrosourea (ENU)-induced mouse mutant with abnormalities in the laminar architecture of the hippocampus and cortex, accompanied by impaired neuronal migration. We show that the causative mutation lies in the guanosine triphosphate (GTP) binding pocket of alpha-1 tubulin (Tuba1) and affects tubulin heterodimer formation. Phenotypic similarity with existing mouse models of lissencephaly led us to screen a cohort of patients with developmental brain anomalies. We identified two patients with de novo mutations in TUBA3, the human homolog of Tuba1. This study demonstrates the utility of ENU mutagenesis in the mouse as a means to discover the basis of human neurodevelopmental disorders.
[Show abstract][Hide abstract] ABSTRACT: Otitis media (OM), inflammation of the middle ear, remains the most common cause of hearing impairment in children. It is also the most common cause of surgery in children in the developed world. There is evidence from studies of the human population and mouse models that there is a significant genetic component predisposing to OM, yet nothing is known about the underlying genetic pathways involved in humans. We identified an N-ethyl-N-nitrosourea-induced dominant mouse mutant Junbo with hearing loss due to chronic suppurative OM and otorrhea. This develops from acute OM that arises spontaneously in the postnatal period, with the age of onset and early severity dependent on the microbiological status of the mice and their air quality. We have identified the causal mutation, a missense change in the C-terminal zinc finger region of the transcription factor Evi1. This protein is expressed in middle ear basal epithelial cells, fibroblasts, and neutrophil leukocytes at postnatal day 13 and 21 when inflammatory changes are underway. The identification and characterization of the Junbo mutant elaborates a novel role for Evi1 in mammalian disease and implicates a new pathway in genetic predisposition to OM.
[Show abstract][Hide abstract] ABSTRACT: The generation of anti-DNA auto-antibodies is characteristic for the human autoimmune condition systemic lupus erythematosus (SLE) and its animal models. However, the contribution of the toll-like receptor (TLR) system of innate immunity receptors and, in particular, TLR9 to this B cell-mediated autoimmune process remains controversial. Here we report that in a novel murine model of SLE, based on hyper-reactive B cell activation mediated by mutant phospholipase Cg2, the genetic deficiency of TLR9 does not protect from spontaneous anti-DNA auto-antibody formation and glomerulonephritis. On the contrary, disease induction is aggravated and additional nucleolar antibody specificity develops in autoimmune TLR9-deficient mice. In vitro studies demonstrate that, in autoimmune-prone mice, dual signaling via the B cell receptor and non-CpG DNA results in synergistic B cell activation in a TLR9-independent manner. These results suggest that engagement of a TLR9-independent DNA activation pathway may promote autoimmunity, while TLR9 signaling can ameliorate SLE-like immune pathology in vivo.
International Immunology 09/2006; 18(8):1211-9. DOI:10.1093/intimm/dxl067 · 2.54 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The C57BL/6J mouse displays glucose intolerance and reduced insulin secretion. The genetic locus underlying this phenotype was mapped to nicotinamide nucleotide transhydrogenase (Nnt) on mouse chromosome 13, a nuclear-encoded mitochondrial protein involved in beta-cell mitochondrial metabolism. C57BL/6J mice have a naturally occurring in-frame five-exon deletion in Nnt that removes exons 7-11. This results in a complete absence of Nnt protein in these mice. We show that transgenic expression of the entire Nnt gene in C57BL/6J mice rescues their impaired insulin secretion and glucose-intolerant phenotype. This study provides direct evidence that Nnt deficiency results in defective insulin secretion and inappropriate glucose homeostasis in male C57BL/6J mice.
[Show abstract][Hide abstract] ABSTRACT: Specification and differentiation of the megakaryocyte and erythroid lineages from a common bipotential progenitor provides a well studied model to dissect binary cell fate decisions. To understand how the distinct megakaryocyte- and erythroid-specific gene programs arise, we have examined the transcriptional regulation of the megakaryocyte erythroid transcription factor GATA1. Hemopoietic-specific mouse (m)GATA1 expression requires the mGata1 enhancer mHS-3.5. Within mHS-3.5, the 3' 179 bp of mHS-3.5 are required for megakaryocyte but not red cell expression. Here, we show mHS-3.5 binds key hemopoietic transcription factors in vivo and is required to maintain histone acetylation at the mGata1 locus in primary megakaryocytes. Analysis of GATA1-LacZ reporter gene expression in transgenic mice shows that a 25-bp element within the 3'-179 bp in mHS-3.5 is critical for megakaryocyte expression. In vitro three DNA binding activities A, B, and C bind to the core of the 25-bp element, and these binding sites are conserved through evolution. Activity A is the zinc finger transcription factor ZBP89 that also binds to other cis elements in the mGata1 locus. Activity B is of particular interest as it is present in primary megakaryocytes but not red cells. Furthermore, mutation analysis in transgenic mice reveals activity B is required for megakaryocyte-specific enhancer function. Bioinformatic analysis shows sequence corresponding to the binding site for activity B is a previously unrecognized motif, present in the cis elements of the Fli1 gene, another important megakaryocyte-specific transcription factor. In summary, we have identified a motif and a DNA binding activity likely to be important in directing a megakaryocyte gene expression program that is distinct from that in red cells.
[Show abstract][Hide abstract] ABSTRACT: The identification of specific genetic loci that contribute to inflammatory and autoimmune diseases has proved difficult due to the contribution of multiple interacting genes, the inherent genetic heterogeneity present in human populations, and a lack of new mouse mutants. By using N-ethyl-N-nitrosourea (ENU) mutagenesis to discover new immune regulators, we identified a point mutation in the murine phospholipase Cg2 (Plcg2) gene that leads to severe spontaneous inflammation and autoimmunity. The disease is composed of an autoimmune component mediated by autoantibody immune complexes and B and T cell independent inflammation. The underlying mechanism is a gain-of-function mutation in Plcg2, which leads to hyperreactive external calcium entry in B cells and expansion of innate inflammatory cells. This mutant identifies Plcg2 as a key regulator in an autoimmune and inflammatory disease mediated by B cells and non-B, non-T haematopoietic cells and emphasizes that by distinct genetic modulation, a single point mutation can lead to a complex immunological phenotype.
[Show abstract][Hide abstract] ABSTRACT: N-ethyl-N-nitrosourea (ENU) introduces mutations throughout the mouse genome at relatively high efficiency. Successful high-throughput phenotype screens have been reported and alternative screens using sequence-based approaches have been proposed. For the purpose of generating an allelic series in selected genes by a sequence-based approach, we have constructed an archive of over 4000 DNA samples from individual F1 ENU-mutagenized mice paralleled by frozen sperm samples. Together with our previously reported archive, the total size now exceeds 6000 individuals. A gene-based screen of 27.4 Mbp of DNA, carried out using denaturing high-performance liquid chromatography (DHPLC), found a mutation rate of 1 in 1.01 Mbp of which 1 in 1.82 Mbp were potentially functional. Screening of whole or selected regions of genes on subsets of the archive has allowed us to identify 15 new alleles from 9 genes out of 15 tested. This is a powerful adjunct to conventional mutagenesis strategies and has the advantage of generating a variety of alleles with potentially different phenotypic outcomes that facilitate the investigation of gene function. It is now available to academic collaborators as a community resource.
[Show abstract][Hide abstract] ABSTRACT: Splenectomized individuals are prone to overwhelming infections with encapsulated bacteria and splenectomy of mice increases susceptibility to streptococcal infections, yet the exact mechanism by which the spleen protects against such infections is unknown. Using congenitally asplenic mice as a model, we show that the spleen is essential for the generation of B-1a cells, a B cell population that cooperates with the innate immune system to control early bacterial and viral growth. Splenectomy of wild-type mice further demonstrated that the spleen is also important for the survival of B-1a cells. Transfer experiments demonstrate that lack of these cells, as opposed to the absence of the spleen per se, is associated with an inability to mount a rapid immune response against streptococcal polysaccharides. Thus, absence of the spleen and the associated increased susceptibility to streptococcal infections is correlated with lack of B-1a B cells. These findings reveal a hitherto unknown role of the spleen in generating and maintaining the B-1a B cell pool.
Journal of Experimental Medicine 04/2002; 195(6):771-80. DOI:10.1084/jem.20011140 · 12.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Calpains are calcium-dependent intracellular nonlysosomal proteases that are believed to participate in signal transduction. In vertebrates, five different calpains have so far been identified, of which three, mu-, m-, and mu/m-calpain, are ubiquitously expressed while the other two, nCL-1 (p94) and nCL-2, exhibit a restricted tissue distribution. We have identified two new vertebrate calpain genes, Capn5 and Capn6. The human and mouse amino acid sequences of these new calpains are the most divergent of the vertebrate calpains identified. They possess most of the residues conserved in calpain family members but the C-terminal region lacks any homology to the calmodulin-like domain of other vertebrate calpains. They both exhibit significant homology over the entire coding region to the protein encoded by the gene tra-3, involved in nematode sex determination, and Capn5 may represent its vertebrate orthologue. The predicted Capn6 protein lacks critical active site residues and may not be proteolytically active. Both genes are differentially expressed in human tissues with highest RNA levels for Capn5 occurring in the testis, liver, trachea, colon, and kidney, while Capn6 is highly expressed only in the placenta sample of the 50 tissues examined. Phylogenetic analysis suggests that the vertebrate calpains arose through a series of gene duplication events that began before the initial divergence of the vertebrate and invertebrate lineages. The discovery of these two new calpains highlights a hitherto unknown complexity of the calpain family with subclasses perhaps possessing different modes of regulation.
[Show abstract][Hide abstract] ABSTRACT: The somatic V(D)J recombination for the assembly of the Ig and TCR genes is mediated by the recombination signal sequences (Rss) and the V(D)J recombinase. A cDNA clone was isolated from a lambda gt11 expression library made from mouse thymocyte poly(A)+ RNA, using the Rss as a ligand. The deduced amino acid sequence of the putative protein, designated Recognition component (Rc), reveals a pair of Cys2-His2 zinc fingers followed by a Glu- and Asp-rich acidic domain. In addition, there are five copies of the Ser/Thr-Pro-X-Arg/Lys sequence, which are putative DNA binding units. The zinc finger-acidic domain structures present in Rc are also found in several enhancer binding proteins, such as those for the kappa B motif of the Ig kappa light chain enhancer or related sequences. Bacterial fusion proteins for Rc bind preferentially to the Rss heptamer and to the kappa B motif. The dual affinities of Rc for the Rss heptamer and the kappa B motif suggest a possible link between Ig transcription and somatic recombination. The formation of multiple 'gel-shifted' DNA-protein complexes for Rc and its DNA ligand suggests that these complexes tend to multimerize.
Nucleic Acids Research 12/1993; 21(22):5067-73. DOI:10.1093/nar/21.22.5067 · 9.11 Impact Factor