A spontaneous mutation in contactin 1 in the mouse

Mutations in the gene encoding the immunoglobulin-superfamily member cell adhesion molecule contactin1 (CNTN1) cause lethal congenital myopathy in human patients and neurodevelopmental phenotypes in knockout mice. Whether the mutant mice provide an accurate model of the human disease is unclear; resolving this will require additional functional tests of the neuromuscular system and examination of Cntn1 mutations on different genetic backgrounds that may influence the phenotype. Toward these ends, we have analyzed a new, spontaneous mutation in the mouse Cntn1 gene that arose in a BALB/c genetic background. The overt phenotype is very similar to the knockout of Cntn1, with affected animals having reduced body weight, a failure to thrive, locomotor abnormalities, and a lifespan of 2-3 weeks. Mice homozygous for the new allele have CNTN1 protein undetectable by western blotting, suggesting that it is a null or very severe hypomorph. In an analysis of neuromuscular function, neuromuscular junctions had normal morphology, consistent with previous studies in knockout mice, and the muscles were able to generate appropriate force when normalized for their reduced size in late stage animals. Therefore, the Cntn1 mutant mice do not show evidence for a myopathy, but instead the phenotype is likely to be caused by dysfunction in the nervous system. Given the similarity of CNTN1 to other Ig-superfamily proteins such as DSCAMs, we also characterized the expression and localization of Cntn1 in the retinas of mutant mice for developmental defects. Despite widespread expression, no anomalies in retinal anatomy were detected histologically or using a battery of cell-type specific antibodies. We therefore conclude that the phenotype of the Cntn1 mice arises from dysfunction in the brain, spinal cord or peripheral nervous system, and is similar in either a BALB/c or B6;129;Black Swiss background, raising a possible discordance between the mouse and human phenotypes resulting from Cntn1 mutations.     

A new spontaneous mouse mutation in the Kcne1 gene

A new mouse mutant, punk rocker (allele symbol Kcne1 ^pkr ), arose spontaneously on a C57BL/10J inbred strain background and is characterized by a distinctive head-tossing, circling, and ataxic phenotype. It is also profoundly and bilaterally deaf. The mutation resides in the Kcne1 gene on Chromosome (Chr) 16 and has been identified as a single base change within the coding region of the third exon. The C to T nucleotide substitution causes an arginine to be altered to a termination codon at amino acid position 67, and predictably this will result in a significantly truncated protein product. The Kcne1 ^pkr mutant represents the first spontaneous mouse model for the human disorder, Jervell and Lange-Nielsen syndrome, associated with mutations in the homologous KCNE1 gene on human Chr 21. Received: 20 April 2000 / Accepted: 2 June 2000     

A novel missense mutation in lysosomal sulfamidase is the basis of MPS III A in a spontaneous mouse mutant

Sanfilippo syndrome type III A (Mucopolysaccharidosis (MPS) III A) is a rare, autosomal recessive, lysosomal storage disease, characterized by the accumulation of heparan sulfate and the loss of function of lysosomal heparan N-sulfatase activity. The disease leads to devastating mental and physical consequences and a mouse model that can be used to explore gene therapy and enzyme or cell replacement therapies is needed. We have previously identified a mouse with low sulfamidase activity and symptoms and pathologies typical of MPS III A (Bhaumik, M., Muller, V. J., Rozaklis, T., Johnson, L., Dobrenis, K., Bhattacharyya, R., Wurzelmann, S., Finamore, P., Hopwood, J. J., Walkley, S. U., and Stanley, P. [1999] A mouse model for mucopolysaccharidosis type III A (Sanfilippo syndrome). Glycobiology 9, 1389--1396). We now show that the sulfamidase gene of the MPS III A mouse carries a novel mutation (G91A) that gives an amino acid change (D31N) likely to interfere with the coordination of a divalent metal ion in the active site of this sulfatase. This spontaneous mouse mutant is an excellent model for MPS III A in humans as this disease often arises due to a missense mutation in lysosomal sulfamidase.     

Kit基因无义突变导致W-3Bao小鼠显性白斑形成

Kit(W)基因是一种原癌基因,在小鼠中该基因位于第5号染色体距着丝粒约42 cM处,其编码的蛋白质是具有酪氨酸激酶活性的干细胞生长因子受体,为酪氨酸激酶受体信号通路的跨膜分子。在人类及小鼠,kit及其配体kitl突变都可能引起不同程度的贫血、肥大细胞减少、毛色变白和生育能力下降或丧失等症状(Rajaraman et al.,2002;Broudy,1997;Rajaraman et al.,2003;Kapur et al.,1999),同源的kit基因突变在猪及禽类都表现为显性的白色斑点(邓素华等,2000)。在先前的研究中,本课题组通过ENU诱变获得6种白斑突变小鼠,通过连锁分析法以微卫星为连锁标…     

A BLOC-1 mutation screen reveals a novel BLOC1S3 mutation in Hermansky-Pudlak Syndrome type 8

Hermansky-Pudlak Syndrome (HPS) is a genetically heterogeneous disorder of lysosome-related organelle biogenesis and is characterized by oculocutaneous albinism and a bleeding diathesis. Over the past decade, we screened 250 patients with HPS-like symptoms for mutations in the genes responsible for HPS subtypes 1-6. We identified 38 individuals with no functional mutations, and therefore, we analyzed all eight genes encoding the biogenesis of lysosome-related organelles complex-1 (BLOC-1) proteins in these individuals. Here, we describe the identification of a novel nonsense mutation in BLOC1S3 (HPS-8) in a 6-yr-old Iranian boy. This mutation caused nonsense-mediated decay of BLOC1S3 mRNA and destabilized the BLOC-1 complex. Our patient's melanocytes showed aberrant localization of TYRP1, with increased plasma membrane trafficking. These findings confirm a common cellular defect for HPS patients with defects in BLOC-1 subunits. We identified only two patients with BLOC-1 defects in our cohort, suggesting that other HPS genes remain to be identified.     

Genomic analysis of a novel spontaneous albino C57BL/6N mouse strain

We report an albino C57BL/6N mouse strain carrying a spontaneous mutation in the tyrosinase gene (C57BL/6N‐Tyr^cWTSI). Deep whole genome sequencing of founder mice revealed very little divergence from C57BL/6NJ and C57BL/6N (Taconic). This coisogenic strain will be of great utility for the International Mouse Phenotyping Consortium (IMPC), which uses the EUCOMM/KOMP targeted C57BL/6N ES cell resource, and other investigators wishing to work on a defined C57BL/6N background. genesis 51:523–528. © 2013 The Authors. Genesis Published by Wiley Periodicals, Inc.     

A new mouse model of spontaneous diabetes derived from ddY strain.

By the selective breeding of obese male mice of the ddY strain and using indices of the heavy body weight and appearance of urinary glucose, we established two inbred strains in 1992: one with obesity and urinary glucose (Tsumura, Suzuki, Obese Diabetes: TSOD) and the other without them (Tsumura, Suzuki, Non Obesity: TSNO). The male TSOD mice constantly showed signs of obesity and urinary glucose with increases in food and water intake, body weight and some fat weight. The body mass index (BMI) clearly showed moderate obesity. Increases in the levels of diabetic blood parameters (glucose, insulin and lipids) were also found in males, in which the levels of blood glucose and insulin were high to the ages past the growth peak. In the histological studies, pancreatic islets of the TSOD males were found hypertrophic without any signs of insulitis or fibrous formation. Among these diabetic characteristics, some of which were similar to the reported models of non-insulin-dependent diabetes mellitus (NIDDM), the stable appearances of the hyperglycemia, the hyperinsulinemia and the hypertrophy of pancreatic islets to the ages past the growth peak were the prominent features. In these respect the TSOD mouse may be a useful model for researching the mechanisms of human diabetes and its complications.     

Neuromuscular ataxia: a new spontaneous mutation in the mouse

Neuromuscular ataxia, nma, is a new autosomal recessive mutation that arose spontaneously in CBA/J inbred mice at The Jackson Laboratory. The mutation, now maintained on the B6C3FeF₁ hybrid background, when homozygous, causes small size, uncoordinated gait, dysmetria, dystonia, general weakness, and death shortly after weaning. No biochemical or morphological abnormalities have been detected. We used an intercross between the B6C3FeF₁ mutant and CAST/Ei to map the nma mutation to the proximal end of Chr 12. The most likely gene order places the mutation between D12Mit270 and D12Mit54, non-recombinant with D12Mit2 in 96 tested meioses. Received: 27 March 2000 / Accepted: 17 May 2000     

DNA sequence analysis of spontaneous mutation in a PolA1 strain of Escherichia coli indicates sequence-specific effects

Summary The sequences of a collection of 261 spontaneous lacI^- mutants recovered in a PolA^- strain of Escherichia coli have indicated an increase in the frequency of most classes of mutation in this strain. Among base substitutions in lacI, a preference for transversions over transitions was observed. In addition, a single transition in the lac operator was enhanced 8-fold. More significantly, of 18 frameshifts, 12 occurred adjacent to a 5-GTGG-3 sequence. Likewise, 15 of 24 deletions and 2 of 10 duplications had 5-GTGG-3 sequences at one or both endpoints. We speculate that the prevalence of mutations at these specific sequences reflects the persistence of strand discontinuities that enhance the opportunity for mutagenic mishaps. Further, 5-GTGG-3 sequences apparently represent sites where DNA polymerase I is involved in some aspect of DNA metabolism. These results strengthen the view that DNA context contributes an important component to spontaneous mutagenesis and indicate an anti-mutagenic role for DNA polymerase I.     

A novel Phex mutation in a new mouse model of hypophosphatemic rickets

X-linked hypophosphatemic rickets (XLH) is a dominantly inherited disease characterized by renal phosphate wasting, aberrant vitamin D metabolism, and defective bone mineralization. It is known that XLH in humans and in certain mouse models is caused by inactivating mutations in PHEX/Phex (phosphate-regulating gene with homologies to endopeptidases on the X chromosome). By a genome-wide N-ethyl-N-nitrosourea (ENU)-induced mutagenesis screen in mice, we identified a dominant mouse mutation that exhibits the classic clinical manifestations of XLH, including growth retardation, skeletal abnormalities (rickets/osteomalacia), hypophosphatemia, and increased serum alkaline phosphatase (ALP) levels. Mapping and sequencing revealed that these mice carry a point mutation in exon 14 of the Phex gene that introduces a stop codon at amino acid 496 of the coding sequence (Phex(Jrt) also published as Phex(K496X) [Ichikawa et al., 2012]). Fgf23 mRNA expression as well as that of osteocalcin, bone sialoprotein, and matrix extracellular phosphoglycoprotein was upregulated in male mutant long bone, but that of sclerostin was unaffected. Although Phex mRNA is expressed in bone from mutant hemizygous male mice (Phex(Jrt)/Y mice), no Phex protein was detected in immunoblots of femoral bone protein. Stromal cultures from mutant bone marrow were indistinguishable from those of wild-type mice with respect to differentiation and mineralization. The ability of Phex(Jrt)/Y osteoblasts to mineralize and the altered expression levels of matrix proteins compared with the well-studied Hyp mice makes it a unique model with which to further explore the clinical manifestations of XLH and its link to FGF23 as well as to evaluate potential new therapeutic strategies.     

A spontaneous albino mutant of Ceratocystis resinifera results from a point mutation in the polyketide synthase gene, PKS1

We characterized a spontaneous albino mutant of Ceratocystis resinifera. Compared with the wild-type progenitor strain, the albino mutant had a reduced linear growth on culture medium, but its growth on lodgepole pine sapwood was unaffected. The albino mutant did not produce any coloured pigment on agar media or wood. However, upon exposure to exogenous scytalone, an intermediate metabolite of the melanin pathway, the production of a brownish melanin was restored. This suggests that the albino phenotype resulted from a mutation affecting the melanin synthesis pathway, upstream of the scytalone synthesis step. Melanin production was restored in the mutant by transforming it with a wild-type copy of the Ceratocystis resinifera polyketide synthase gene, PKS1. The complemented transformants produced melanin, indicating that the PKS1 gene was defective in the albino mutant. Sequence analysis revealed that the PKS1 allele found in the albino contained a single point mutation that resulted in an amino acid change from serine to proline at the 3' end of the beta-ketoacyl synthase motif.     

A novel mouse Chromosome 2 congenic strain with obesity phenotypes

Linkage studies have identified many chromosomal regions containing obesity genes in mice. However, only a few of these quantitative trait loci (QTLs) have been used to guide the production of congenic mouse strains that retain obesity phenotypes. We seek to identify chromosomal regions containing obesity genes in the BSB model of spontaneous obesity because the BSB model is a multigenic obesity model. Previous studies identified QTLs on Chromosomes (Chrs) 2, 6, 7,12, and 15. BSB mice are made by backcross of lean C57BL/6J × Mus spretus. F₁s were backcrossed to C57BL/6J mice to produce BSB progeny. We have constructed a new BSB cross and produced congenic mice with obesity phenotypes by marker-directed selection called B6.S–D2Mit194–D2Mit311. We found a highly significant QTL for percentage body lipid on Chr 2 just proximal to the Agouti locus. Chr 2 congenics were constructed to determine whether the main effects would be detectable. We observed highly significant linkage of the Chr 2 congenic containing Agouti and containing markers distal to D2Mit311 and proximal to D2Mit194. Thus, this congenic contains approximately 14.6 cM or 30 Mb (about 1.1% of the spretus mouse genome) and several hundred genes. The obesity phenotype of the QTL is retained in the congenic. The congenic can now be used to model the genetic and physiological basis for a relatively simple, perhaps monogenic, obesity.     

Association of the Breast Cancer Antiestrogen Resistance Protein 1 (BCAR1) and BCAR3 Scaffolding Proteins in Cell Signaling and Antiestrogen Resistance

Most breast cancers are estrogen receptor-positive and treated with antiestrogens, but aberrant signaling networks can induce drug resistance. One of these networks involves the scaffolding protein BCAR1/p130CAS, which regulates cell growth and migration/invasion. A less investigated scaffolding protein that also confers antiestrogen resistance is the SH2 domain-containing protein BCAR3. BCAR1 and BCAR3 bind tightly to each other through their C-terminal domains, thus potentially connecting their associated signaling networks. However, recent studies using BCAR1 and BCAR3 interaction mutants concluded that association between the two proteins is not critical for many of their interrelated activities regulating breast cancer malignancy. We report that these previously used BCAR mutations fail to cause adequate loss-of-function of the complex. By using structure-based BCAR1 and BCAR3 mutants that lack the ability to interact, we show that BCAR3-induced antiestrogen resistance in MCF7 breast cancer cells critically depends on its ability to bind BCAR1. Interaction with BCAR3 increases the levels of phosphorylated BCAR1, ultimately potentiating BCAR1-dependent antiestrogen resistance. Furthermore, antiestrogen resistance in cells overexpressing BCAR1/BCAR3 correlates with increased ERK1/2 activity. Inhibiting ERK1/2 through overexpression of the regulatory protein PEA15 negates the resistance, revealing a key role for ERK1/2 in BCAR1/BCAR3-induced antiestrogen resistance. Reverse-phase protein array data show that PEA15 levels in invasive breast cancers correlate with patient survival, suggesting that PEA15 can override ERK1/2 activation by BCAR1/BCAR3 and other upstream regulators. We further uncovered that the BCAR3-related NSP3 can also promote antiestrogen resistance. Thus, strategies to disrupt BCAR1-BCAR3/NSP3 complexes and associated signaling networks could ultimately lead to new breast cancer therapies.