Biomedical subjects

Roderick T Bronson

Publications and source records attributed to Roderick T Bronson.

At least 37 records · Page 2Linked to original sources

PubMed2005

Further characterization of reproductive abnormalities in mCd59b knockout mice: a potential new function of mCd59 in male reproduction.

CD59 is a GPI-linked membrane protein that inhibits formation of the membrane attack complex of complement. We reported recently that mice have two CD59 genes (termed mCd59a and mCd59b), and that the targeted deletion of mCd59b (mCd59b-/-) results in spontaneous hemolytic anemia and progressive loss of male fertility. Further studies of the reproductive abnormalities in mCd59b-/- mice reported in this study revealed the presence of abnormal multinucleated cells and increased apoptotic cells within the walls of the seminiferous tubules, and a decrease in the number, motility, and viability of sperm associated with a significant increase in abnormal sperm morphologies. Both the capacitation-associated tyrosine phosphorylation and the ionophore-induced acrosome reaction as well as luteinizing hormone, follicle-stimulating hormone, and testosterone serum levels were similar in mCd59b-/- and mCd59b+/+. Surprisingly, the functional deficiency of the complement protein C3 did not rescue the abnormal reproductive phenotype of mCd59b-/-, although it was efficient in rescuing their hemolytic anemia. These results indicate that the male reproductive abnormalities in mCd59b-/- are complement-independent, and that mCd59 may have a novel function in spermatogenesis that is most likely unrelated to its function as an inhibitor of membrane attack complex formation.

Anemia, Hemolytic↗

PubMed2005

Tumor-secreted vascular endothelial growth factor-C is necessary for prostate cancer lymphangiogenesis, but lymphangiogenesis is unnecessary for lymph node metastasis.

Dissemination to draining lymph nodes is a frequent first step in prostate cancer metastasis. Although tumors metastasize to lymph nodes via the lymphatics, the importance of lymphangiogenesis in mediating the process remains controversial. Here, we inhibit intratumoral lymphangiogenesis in s.c. and surgical orthotopic implantation mouse models of human prostate cancer using several strategies. Stable expression of small interfering RNAs (siRNA) targeted against human vascular endothelial growth factor-C (VEGF-C) in PC-3 cells reduced intratumoral lymphatics by 99% in s.c. tumors, indicating that tumor-secreted VEGF-C is necessary for lymphangiogenesis. Expression of siRNAs against human VEGF-A somewhat reduced tumor lymphangiogenesis. Secretion of a soluble VEGF receptor-3/Flt4 fusion protein by PC-3 cells reduced intratumoral lymphatics by 100% in s.c. tumors. Combination of soluble Flt4 and VEGF-C siRNA yielded >92% reduction of intratumoral lymphatics in orthotopic prostate tumors. However, metastasis to lymph nodes was not significantly affected regardless of intratumoral lymphatic vessel density. The abundance of marginal lymphatics at the tumor-stromal interface was unchanged in orthotopic tumors whose intratumoral lymphatics were inhibited, suggesting that these marginal vessels could be sufficient for lymph node metastasis. Hematogenous metastasis (blood tumor burden, lung metastasis) correlated with degree of lymph node invasion. We also analyzed the lymphatics in spontaneous transgenic adenocarcinomas of the mouse prostate which metastasize to lymph nodes. Progression from well-differentiated prostate intraepithelial neoplasia to metastatic, undifferentiated adenocarcinoma was accompanied by loss of lymphatics. These results suggest that tumor-secreted VEGF-C and, to a lesser extent, VEGF-A, are important for inducing prostate cancer intratumoral lymphangiogenesis but are unnecessary for lymph node metastasis.

Adenocarcinoma↗

PubMed2005

Cytokinesis failure generating tetraploids promotes tumorigenesis in p53-null cells.

A long-standing hypothesis on tumorigenesis is that cell division failure, generating genetically unstable tetraploid cells, facilitates the development of aneuploid malignancies. Here we test this idea by transiently blocking cytokinesis in p53-null (p53-/-) mouse mammary epithelial cells (MMECs), enabling the isolation of diploid and tetraploid cultures. The tetraploid cells had an increase in the frequency of whole-chromosome mis-segregation and chromosomal rearrangements. Only the tetraploid cells were transformed in vitro after exposure to a carcinogen. Furthermore, in the absence of carcinogen, only the tetraploid cells gave rise to malignant mammary epithelial cancers when transplanted subcutaneously into nude mice. These tumours all contained numerous non-reciprocal translocations and an 8-30-fold amplification of a chromosomal region containing a cluster of matrix metalloproteinase (MMP) genes. MMP overexpression is linked to mammary tumours in humans and animal models. Thus, tetraploidy enhances the frequency of chromosomal alterations and promotes tumour development in p53-/- MMECs.

Animals↗

PubMed2005

Targeted disruption of Mig-6 in the mouse genome leads to early onset degenerative joint disease.

Degenerative joint disease, also known as osteoarthritis, is the most common joint disorder in human beings. The molecular mechanism underlying this disease is not fully understood. Here, we report that disruption of mitogen-inducible gene 6 (Mig-6) in mice by homologous recombination leads to early onset degenerative joint disease, which is revealed by simultaneous enlargement and deformity of multiple joints, degradation of articular cartilage, and the development of bony outgrowths or osteophyte formation within joint space. The osteophyte formation appears to be derived from proliferation of mesenchymal progenitor cells followed by differentiation into chondrocytes. Absence of the Rag2 gene does not rescue the joint phenotype, excluding a role for the acquired immune system in the development of this disease. Our results provide insight into the mechanism of osteoarthritis by showing that loss of Mig-6 leads to early onset of this disease, implying that this gene or its pathway is important in normal joint maintenance. Because of the striking similarity of osteoarthritis in humans and mice, the Mig-6 mutant mouse should provide a useful animal model for studying the mechanism of this disease and for testing drugs or therapies for treating osteoarthritis.

Age of Onset↗

PubMed2005

Mice lacking the p53/p63 target gene Perp are resistant to papilloma development.

Perp is a target of the p53 tumor suppressor involved in the DNA damage-induced apoptosis pathway. In addition, Perp is a target of the p53-related transcription factor p63 during skin development, where it participates in cell-cell adhesion mediated through desmosomes. Here we test the role of Perp in tumorigenesis in a two-step skin carcinogenesis model system. We find that mice lacking Perp in the skin are resistant to papilloma development, displaying fewer and smaller papillomas than wild-type mice. Proliferation levels, apoptotic indices and differentiation patterns are similar in the skin of treated Perp-deficient and wild-type mice. Instead, impaired adhesion through aberrant desmosome assembly may explain the diminished tumor development in the absence of Perp. These studies indicate that in certain contexts, Perp is required for efficient carcinogenesis and suggest a role for intact cell-cell adhesion in supporting tumor development in these settings.

9,10-Dimethyl-1,2-benzanthracene↗

PubMed2005

Identification of bronchioalveolar stem cells in normal lung and lung cancer.

Injury models have suggested that the lung contains anatomically and functionally distinct epithelial stem cell populations. We have isolated such a regional pulmonary stem cell population, termed bronchioalveolar stem cells (BASCs). Identified at the bronchioalveolar duct junction, BASCs were resistant to bronchiolar and alveolar damage and proliferated during epithelial cell renewal in vivo. BASCs exhibited self-renewal and were multipotent in clonal assays, highlighting their stem cell properties. Furthermore, BASCs expanded in response to oncogenic K-ras in culture and in precursors of lung tumors in vivo. These data support the hypothesis that BASCs are a stem cell population that maintains the bronchiolar Clara cells and alveolar cells of the distal lung and that their transformed counterparts give rise to adenocarcinoma. Although bronchiolar cells and alveolar cells are proposed to be the precursor cells of adenocarcinoma, this work points to BASCs as the putative cells of origin for this subtype of lung cancer.

Adenocarcinoma, Bronchiolo-Alveolar↗

PubMed2005

Essential role of endothelial Notch1 in angiogenesis.

BACKGROUND: Notch signaling influences binary cell fate decisions in a variety of tissues. The Notch1 receptor is widely expressed during embryogenesis and is essential for embryonic development. Loss of global Notch1 function results in early embryonic lethality, but the cell type responsible for this defect is not known. Here, we identify the endothelium as the primary target tissue affected by Notch1 signaling. METHODS AND RESULTS: We generated an endothelium-specific deletion of Notch1 using Tie2Cre and conditional Notch1(flox/flox) mice. Mutant embryos lacking endothelial Notch1 died at approximately embryonic day 10.5 with profound vascular defects in placenta, yolk sac, and embryo proper, whereas heterozygous deletion had no effect. In yolk sacs of mutant embryos, endothelial cells formed a primary vascular plexus indicative of intact vasculogenesis but failed to induce the secondary vascular remodeling required to form a mature network of well-organized large and small blood vessels, which demonstrates a defect in angiogenesis. These vascular defects were also evident in the placenta, where blood vessels failed to invade the placental labyrinth, and in the embryo proper, where defective blood vessel maturation led to pericardial and intersomitic hemorrhage. Enhanced activation of caspase-3 was detected in endothelial and neural cells of mutant mice, which resulted in enhanced apoptotic degeneration of somites and the neural tube. CONCLUSIONS: These findings recapitulate the vascular phenotype of global Notch1-/- mutants and indicate an essential cell-autonomous role of Notch1 signaling in the endothelium during vascular development. These results may have important clinical implications with regard to Notch1 signaling in adult angiogenesis.

Animals↗

PubMed2005

New Alström syndrome phenotypes based on the evaluation of 182 cases.

BACKGROUND: Alström syndrome is a recessively inherited genetic disorder characterized by congenital retinal dystrophy that leads to blindness, hearing impairment, childhood obesity, insulin resistance, and type 2 diabetes mellitus. We provide new details on cardiologic, hepatic, gastrointestinal, urologic, pulmonary, and neurobehavioral phenotypes in Alström syndrome and describe the histopathologic findings in 5 individuals. METHODS: We obtained data on 182 patients from clinical examinations, medical record reviews, standardized questionnaires, and personal interviews with physicians and parents. RESULTS: Dilated cardiomyopathy occurred in 60% of patients. Age at onset was either during infancy, often before vision disturbances were noted, or in adolescence or adulthood. There is a risk of recurrence of infantile cardiomyopathy. Hyperinsulinemia (92%) developed in early childhood and progressed to type 2 diabetes mellitus in 82% of those older than 16 years. Hypertriglyceridemia (54%) precipitated pancreatitis in 8 patients. Urologic dysfunction and gastrointestinal disturbances occurred in 48% and 35% of patients, respectively. Fifty-three percent of patients had persistent pulmonary symptoms. Neurologic symptoms in 20% of patients included clonic tic and absence seizures. Developmental motor or language delays were observed in 46% of patients. Fibrotic infiltrations of multiple organs, that is, kidney, heart, liver, lung, urinary bladder, gonads, and pancreas, were observed. CONCLUSIONS: The wide-ranging and complex spectrum of phenotypes reported herein broadens those previously described for Alström syndrome. These findings will aid physicians in making an early and accurate diagnosis and will help effect appropriate monitoring and treatment.

Abnormalities, Multiple↗

PubMed2005

Perp is a p63-regulated gene essential for epithelial integrity.

p63 is a master regulator of stratified epithelial development that is both necessary and sufficient for specifying this multifaceted program. We show here that Perp, a tetraspan membrane protein originally identified as an apoptosis-associated target of the p53 tumor suppressor, is the first direct target of p63 clearly involved in mediating this developmental program in vivo. During embryogenesis, Perp is expressed in an epithelial pattern, and its expression depends on p63. Perp-/- mice die postnatally, with dramatic blistering in stratified epithelia symptomatic of compromised adhesion. Perp localizes specifically to desmosomes, adhesion junctions important for tissue integrity, and numerous structural defects in desmosomes are observed in Perp-deficient skin, suggesting a role for Perp in promoting the stable assembly of desmosomal adhesive complexes. These findings demonstrate that Perp is a key effector in the p63 developmental program, playing an essential role in an adhesion subprogram central to epithelial integrity and homeostasis.

Animals↗

PubMed2005

Coxsackievirus and adenovirus receptor is essential for cardiomyocyte development.

The coxsackievirus and adenovirus receptor (CAR) is a transmembrane protein that is known to be a site of viral attachment and entry, but its physiologic functions are undefined. CAR expression is maximal in neonates and wanes rapidly after birth in organs such as heart, muscle, and brain, suggesting that CAR plays a role in the development of these tissues. Here, we show that CAR deficiency resulted in an embryonic lethal condition associated with cardiac defects. Specifically, commencing approximately 10.5 days postconception (dpc), CAR-/- cardiomyocytes exhibited regional apoptosis evidenced by both histopathologic features of cell death and positive staining for the apoptotic marker cleaved caspase 3. CAR-/- fetuses invariably suffered from degeneration of the myocardial wall and thoracic hemorrhaging, leading to death by 11.5 dpc. These findings are consistent with the view that CAR provides positive survival signals to cardiomyocytes that are essential for normal heart development.

Animals↗

PubMed2005

Loss of the putative tumor suppressor band 4.1B/Dal1 gene is dispensable for normal development and does not predispose to cancer.

The band 4.1 proteins are cytoskeletal proteins, harboring a conserved FERM domain highly homologous to the N-terminal FERM domain of ezrin, radixin, moesin, and merlin. Recently, a truncated form of the 4.1B protein, termed Dal-1, was identified in a screen as down regulated in adenocarcinoma of the lung and was mapped to chromosome 18p11.3, which is lost in 38% of primary non-small cell lung carcinoma tumors. Analysis of several meningiomas has shown that Dal-1 expression was lost in 76% of the tumors. To further elucidate the function of the 4.1B/Dal-1 gene in development and tumorigenesis we generated mice deficient for this allele. The 4.1B/Dal-1 null mice develop normally and are fertile. Rates of cellular proliferation and apoptosis in brain, mammary, and lung tissues from the 4.1B/Dal-1 null mice were indistinguishable from those seen with wild-type mice. Aging studies indicate that these mice do not have a propensity to develop tumors. Analysis of fibroblasts from these mice demonstrated that the growth characteristics and kinetics of these cells were not different from those of cells from the wild-type mice. These findings indicate that the 4.1B gene is not required for normal development and that 4.1B/Dal-1 does not function as a tumor suppressor gene.

Alleles↗

PubMed2004

Mutant p53 gain of function in two mouse models of Li-Fraumeni syndrome.

The p53 tumor suppressor gene is commonly altered in human tumors, predominantly through missense mutations that result in accumulation of mutant p53 protein. These mutations may confer dominant-negative or gain-of-function properties to p53. To ascertain the physiological effects of p53 point mutation, the structural mutant p53R172H and the contact mutant p53R270H (codons 175 and 273 in humans) were engineered into the endogenous p53 locus in mice. p53R270H/+ and p53R172H/+ mice are models of Li-Fraumeni Syndrome; they developed allele-specific tumor spectra distinct from p53+/- mice. In addition, p53R270H/- and p53R172H/- mice developed novel tumors compared to p53-/- mice, including a variety of carcinomas and more frequent endothelial tumors. Dominant effects that varied by allele and function were observed in primary cells derived from p53R270H/+ and p53R172H/+ mice. These results demonstrate that point mutant p53 alleles expressed under physiological control have enhanced oncogenic potential beyond the simple loss of p53 function.

Alleles↗

PubMed2004

Selective ablation of alphav integrins in the central nervous system leads to cerebral hemorrhage, seizures, axonal degeneration and premature death.

Mouse embryos genetically null for all alphav integrins develop intracerebral hemorrhage owing to defective interactions between blood vessels and brain parenchymal cells. Here, we have used conditional knockout technology to address whether the cerebral hemorrhage is due to primary defects in vascular or neural cell types. We show that ablating alphav expression in the vascular endothelium has no detectable effect on cerebral blood vessel development, whereas deletion of alphav expression in central nervous system glial cells leads to embryonic and neonatal cerebral hemorrhage. Conditional deletion of alphav integrin in both central nervous system glia and neurons also leads to cerebral hemorrhage, but additionally to severe neurological defects. Approximately 30% of these mutants develop seizures and die by 4 weeks of age. The remaining mutants survive for several months, but develop axonal deterioration in the spinal cord and cerebellum, leading to ataxia and loss of hindlimb coordination. Collectively, these data provide evidence that alphav integrins on embryonic central nervous system neural cells, particularly glia, are necessary for proper cerebral blood vessel development, and also reveal a novel function for alphav integrins expressed on axons in the postnatal central nervous system.

Animals↗

PubMed2004

Mouse development and cell proliferation in the absence of D-cyclins.

D-type cyclins (cyclins D1, D2, and D3) are regarded as essential links between cell environment and the core cell cycle machinery. We tested the requirement for D-cyclins in mouse development and in proliferation by generating mice lacking all D-cyclins. We found that these cyclin D1(-/-)D2(-/-)D3(-/-) mice develop until mid/late gestation and die due to heart abnormalities combined with a severe anemia. Our analyses revealed that the D-cyclins are critically required for the expansion of hematopoietic stem cells. In contrast, cyclin D-deficient fibroblasts proliferate nearly normally but show increased requirement for mitogenic stimulation in cell cycle re-entry. We found that the proliferation of cyclin D1(-/-)D2(-/-)D3(-/-) cells is resistant to the inhibition by p16(INK4a), but it critically depends on CDK2. Lastly, we found that cells lacking D-cyclins display reduced susceptibility to the oncogenic transformation. Our results reveal the presence of alternative mechanisms that allow cell cycle progression in a cyclin D-independent fashion.

Animals↗

PubMed2004

Susceptibility to astrocytoma in mice mutant for Nf1 and Trp53 is linked to chromosome 11 and subject to epigenetic effects.

Astrocytoma is the most common malignant brain tumor in humans. Loss of the p53 signaling pathway and up-regulation of the ras signaling pathway are common during tumor progression. We have shown previously that mice mutant for Trp53 and Nf1 develop astrocytoma, progressing to glioblastoma, on a C57BL/6J strain background. In contrast, here we present data that mice mutant for Trp53 and Nf1 on a 129S4/SvJae background are highly resistant to developing astrocytoma. Through analysis of F1 progeny, we demonstrate that susceptibility to astrocytoma is linked to chromosome 11, and that the modifier gene(s) responsible for differences in susceptibility is closely linked to Nf1 and Trp53. Furthermore, this modifier of astrocytoma susceptibility is itself epigenetically modified. These data demonstrate that epigenetic effects can have a strong effect on whether cancer develops in the context of mutant ras signaling and mutant p53, and that this mouse model of astrocytoma can be used to identify modifier phenotypes with complex inheritance patterns that would be unidentifiable in humans. Because analysis of gene function in the mouse is often performed on a mixed C57BL/6,129 strain background, these data also provide a powerful example of the potential of these strains to mask interesting gene functions.

Animals↗

PubMed2004

Mouse model of Noonan syndrome reveals cell type- and gene dosage-dependent effects of Ptpn11 mutation.

Noonan syndrome is a common human autosomal dominant birth defect, characterized by short stature, facial abnormalities, heart defects and possibly increased risk of leukemia. Mutations of Ptpn11 (also known as Shp2), which encodes the protein-tyrosine phosphatase Shp2, occur in approximately 50% of individuals with Noonan syndrome, but their molecular, cellular and developmental effects, and the relationship between Noonan syndrome and leukemia, are unclear. We generated mice expressing the Noonan syndrome-associated mutant D61G. When homozygous, the D61G mutant is embryonic lethal, whereas heterozygotes have decreased viability. Surviving Ptpn11(D61G/+) embryos ( approximately 50%) have short stature, craniofacial abnormalities similar to those in Noonan syndrome, and myeloproliferative disease. Severely affected Ptpn11(D61G/+) embryos ( approximately 50%) have multiple cardiac defects similar to those in mice lacking the Ras-GAP protein neurofibromin. Their endocardial cushions have increased Erk activation, but Erk hyperactivation is cell and pathway specific. Our results clarify the relationship between Noonan syndrome and leukemia and show that a single Ptpn11 gain-of-function mutation evokes all major features of Noonan syndrome by acting on multiple developmental lineages in a gene dosage-dependent and pathway-selective manner.

Animals↗

PubMed2004

Disruption of muscle membrane and phenotype divergence in two novel mouse models of dysferlin deficiency.

Limb girdle muscular dystrophy type 2B and Miyoshi myopathy are clinically distinct forms of muscular dystrophy that arise from defects in the dysferlin gene. Here, we report two novel lines of dysferlin-deficient mice obtained by (a) gene targeting and (b) identification of an inbred strain, A/J, bearing a retrotransposon insertion in the dysferlin gene. The mutations in these mice were located at the 3' and 5' ends of the dysferlin gene. Both lines of mice lacked dysferlin and developed a progressive muscular dystrophy with histopathological and ultrastructural features that closely resemble the human disease. Vital staining with Evans blue dye revealed loss of sarcolemmal integrity in both lines of mice, similar to that seen in mdx and caveolin-3 deficient mice. However, in contrast to the latter group of animals, the dysferlin-deficient mice have an intact dystrophin glycoprotein complex and normal levels of caveolin-3. Our findings indicate that muscle membrane disruption and myofiber degeneration in dysferlinopathy were directly mediated by the loss of dysferlin via a new pathogenic mechanism in muscular dystrophies. We also show that the mutation in the A/J mice arose between the late 1970s and the early 1980s, and had become fixed in the production breeding stocks. Therefore, all studies involving the A/J mice or mice derived from A/J, including recombinant inbred, recombinant congenic and chromosome substitution strains, should take into account the dysferlin defect in these strains. These new dysferlin-deficient mice should be useful for elucidating the pathogenic pathway in dysferlinopathy and for developing therapeutic strategies.

Animals↗

PubMed2004

Absence of a reductase, NCB5OR, causes insulin-deficient diabetes.

NCB5OR is a highly conserved NAD(P)H reductase that contains a cytochrome b5-like domain at the N terminus and a cytochrome b5 reductase-like domain at the C terminus. The enzyme is located in the endoplasmic reticulum (ER) and is widely expressed in organs and tissues. Targeted inactivation of this gene in mice has no impact on embryonic or fetal viability. At 4 weeks of age, Ncb5or-/- mice have normal blood glucose levels but impaired glucose tolerance. Isolated Ncb5or-/- islets have markedly impaired glucose- or arginine-stimulated insulin secretion. By 7 weeks of age, these mice develop severe hyperglycemia with markedly decreased serum insulin levels and nearly normal insulin tolerance. As the animals age, there is a progressive loss of beta cells in pancreatic islets, but there is no loss of alpha, delta, or PP cells. Electron microscopy reveals degranulation of beta cells and hypertrophic and hyperplastic mitochondria, some of which contain electron dense inclusions. Four-week-old Ncb5or-/- mice have enhanced sensitivity to the diabetogenic agent streptozotocin. NCB5OR appears to play a critical role in protecting pancreatic beta cells against oxidant stress.

Animals↗