Biomedical subjects

R T Bronson

Publications and source records attributed to R T Bronson.

At least 91 records · Page 5Linked to original sources

PubMed1997

Cerebellar deficient folia (cdf): a new mutation on mouse chromosome 6.

Cerebellar deficient folia, cdf, is a spontaneous autosomal recessive mutation in the mouse with unique pathology; the cerebellar cortex of the cdf/cdf mouse has only 7 folia instead of 10, which is the normal count for the C3H/HeJ strain in which this mutation arose. The cerebellum of the cdf/cdf mouse is hypoplastic and contains mineral deposits in the ventral vermis that are not present in controls. We used an intersubspecific intercross between C3H/HeSnJ-cdf/+ and Mus musculus castaneus (CAST/Ei) to map the cdf mutation to Chromosome (Chr) 6. The most likely gene order is D6Mit16-(cdf, D6Mit3)-D6Mit70-D6Mit29-D6Mit32, which positions cdf distal to lurcher (Lc) and proximal to motor neuron degeneration 2 (mnd2). The definitive visible phenotypes and histopathologies of cdf, Lc, and mnd2 support our mapping evidence that cdf is a distinct gene. The novel pathology of cdf should help elucidate the complicated process of cerebellar folia patterning and development. cdf recombined with mouse atonal homolog 1, Math1, the mouse homolog of the Drosophila atonal gene.

Animals↗

PubMed1997

Immediate-early gene expression in ovine brain after hypothermic circulatory arrest: effects of aptiganel.

BACKGROUND: Altered gene expression occurs in the brain after global ischemia. We have developed a model to examine the effects of cardiopulmonary bypass and hypothermic circulatory arrest (HCA) on the induction of the immediate-early gene c-fos in the brains of neonatal lambs. We then tested the effects of the noncompetitive N-methyl-D-aspartate antagonist, aptiganel hydrochloride (Cerestat), on c-fos expression and neuronal injury. METHODS: Neonatal lambs (weight, 4 to 6 kg) anesthetized with isoflurane were supported by cardiopulmonary bypass, subjected to 90 or 120 minutes of HCA at 15 degrees C, and rewarmed on bypass to 38 degrees C. One hour after cardiopulmonary bypass was terminated, the brains were perfusion fixed and removed for in situ hybridization and immunohistochemical analysis. Some animals survived 3 days before their brains were removed to examine for neuronal necrosis. One group of lambs (n = 20) received aptiganel (2.5 mg/kg). A second group (n = 25) received saline vehicle only. RESULTS: Increasing duration of HCA induced a corresponding increase in c-fos messenger RNA expression throughout the hippocampal formation and cortex. However, Fos protein synthesis peaked after 90 minutes of HCA and decreased significantly (p < 0.01) after 120 minutes of HCA. Aptiganel administration caused a significant decrease in (p < 0.001) c-fos messenger RNA expression and Fos protein synthesis after 90 minutes of HCA and preserved Fos protein synthesis after 120 minutes of HCA. Neuronal necrosis was observed in the brains of vehicle-treated lambs after 120 minutes of HCA but was significantly decreased (p < 0.05) in the lambs given aptiganel. CONCLUSIONS: These experiments indicate that the transcriptional processes of immediate-early genes remain intact, whereas translational processes are impaired after prolonged HCA. The inability to synthesize Fos proteins after 120 minutes of HCA was associated with neuronal degeneration. Aptiganel preserved translational processes and caused a significant improvement in the neurologic outcome.

Animals↗

PubMed1997

The vibrator mutation causes neurodegeneration via reduced expression of PITP alpha: positional complementation cloning and extragenic suppression.

The mouse vibrator mutation causes an early-onset progressive action tremor, degeneration of brain stem and spinal cord neurons, and juvenile death. We cloned the vibrator mutation using an in vivo positional complementation approach and complete resequencing of the resulting 76 kb critical region from vibrator and its parental chromosome. The mutation is an intracisternal A particle retroposon insertion in intron 4 of the phosphatidylinositol transfer protein alpha gene, causing a 5-fold reduction in RNA and protein levels. Expression of neurofilament light chain is also reduced in vibrator, suggesting one signaling pathway that may underlie vibrator pathology. The vibrator phenotype is suppressed in one intercross. We performed a complete genome scan and mapped a major suppressor locus (Mvb-1) to proximal chromosome 19.

Alleles↗

PubMed1997

Failure of lymphopoiesis after adoptive transfer of NF-kappaB-deficient fetal liver cells.

Mice deficient in the p65 subunit of NF-kappaB die during fetal development. Introduction of p50/p65-deficient fetal liver cells into lethally irradiated hosts resulted in a severe deficit of fetal liver-derived lymphocytes and their immediate precursors but an overabundance of fetal liver-derived granulocytes. Surprisingly, simultaneous transplantation of wild-type bone marrow cells rescued the production of p50/p65-deficient lymphocytes. Expression of immunoglobulin K light chains on these rescued NF-kappaB-deficient B lymphocytes was normal. These results suggest that while p50 and p65 do not regulate the maturation of pre-B cells, NF-kappaB mediates the development or survival of an early lymphocyte precursor through regulation of an extracellular factor.

Adoptive Transfer↗

PubMed1997

Functional screening of 2 Mb of human chromosome 21q22.2 in transgenic mice implicates minibrain in learning defects associated with Down syndrome.

Using Down syndrome as a model for complex trait analysis, we sought to identify loci from chromosome 21q22.2 which, when present in an extra dose, contribute to learning abnormalities. We generated low-copy-number transgenic mice, containing four different yeast artificial chromosomes (YACs) that together cover approximately 2 megabases (Mb) of contiguous DNA from 21q22.2. We subjected independent lines derived from each of these YAC transgenes to a series of behavioural and learning assays. Two of the four YACs caused defects in learning and memory in the transgenic animals, while the other two YACs had no effect. The most severe defects were caused by a 570-kb YAC; the interval responsible for these defects was narrowed to a 180-kb critical region as a consequence of YAC fragmentation. This region contains the human homologue of a Drosophila gene, minibrain, and strongly implicates it in learning defects associated with Down syndrome.

Animals↗

PubMed1997

Temporal and spatial specificity of PDGF alpha receptor promoter in transgenic mice.

Aberrant expression of the platelet-derived growth factor alpha receptor (PDGF alpha R) has been linked to developmental abnormalities in vertebrate models, and has been implicated in multiple disease states in humans. To identify cis-acting regulatory elements that dictate expression of this receptor, we generated transgenic mice bearing the reporter gene beta-galactosidase (lacZ) under the control of a 6-kb promoter sequence. Expression of lacZ was monitored throughout embryonic development, with special focus on nervous tissue, skeleton, and several organ systems wherein PDGF alpha R expression is thought to play a pivotal role. In several independent transgenic mouse strains, lacZ expression recapitulated predominant features of PDGF alpha R gene expression during mouse development. These results demonstrate that critical tissue-specific regulatory elements for PDGF alpha R expression are located within a 6-kb upstream region of the PDGF alpha R gene.

Animals↗

PubMed1996

Cyclin D2 is an FSH-responsive gene involved in gonadal cell proliferation and oncogenesis.

THE D-type cyclins (D1, D2 and D3) are critical governors of the cell-cycle clock apparatus during the G1 phase of the mammalian cell cycle. These three D-type cyclins are expressed in overlapping, apparently redundant fashion in the proliferating tissues. To investigate why mammalian cells need three distinct D-type cyclins, we have generated mice bearing a disrupted cyclin D2 gene by using gene targeting in embryonic stem cells. Cyclin D2-deficient females are sterile owing to the inability of ovarian granulosa cells to proliferate normally in response to follicle-stimulating hormone (FSH), whereas mutant males display hypoplastic testes. In ovarian granulosa cells, cyclin D2 is specifically induced by FSH via a cyclic-AMP-dependent pathway, indicating that expression of the various D-type cyclins is under control of distinct intracellular signalling pathways. The hypoplasia seen in cyclin D2(-/-) ovaries and testes prompted us to examine human cancers deriving from corresponding tissues. We find that some human ovarian and testicular tumours contain high levels of cyclin D2 messenger RNA.

Animals↗

PubMed1996

Evidence that lysosomal storage of proteolipids is a cell autonomous process in the motor neuron degeneration (mnd) mouse, a model of neuronal ceroid lipofuscinosis.

The motor neuron degeneration (mnd) mouse has been documented to accumulate proteolipid and thus is a model of neuronal ceroid lipofuscinosis [Dunn, W.A., Raizada, M.K., Vogt, E.S. and Brown, E.A., Int. J. Dev. Neurosci., 12 (1994) 185-196; Faust, J.R., Rodman, J.S., Daniel, P.F., Dice, J.F. and Bronson, R.T., J. Biol. Chem., 269 (1994) 10150-10155]. While accumulation of proteolipid in the hippocampus of chimeric mice composed of mnd and +/+ cells was found to be proportional to the contribution of mnd in the brain, accumulation within individual cells was the same for cells from chimeric and age-matched mnd mice. Bone marrow transplantation was used to altering the milieu of circulating factors to determine whether this might modify the disease phenotype in mnd mice. Transplantation of bone marrow in neonatal or young mice did not reduce the age-associated accumulation of proteolipid within hippocampal neurons. The results of these experiments indicate that mnd results in a cell autonomous defect.

Aging↗

PubMed1996

Effects of caloric restriction on expression of testicular cytochrome P450 enzymes associated with the metabolic activation of carcinogens.

Previous work demonstrated that microsomal cytochrome P4502A1 (CYP2A1) is expressed in rat testicular Leydig cells. The present study investigates the effects of diet, age, and strain on rat testicular CYP2A1 expression and assesses the potential role of testicular CYP2A1 in the metabolic activation of carcinogens. In ad libitum-fed 18-week-old Fischer 344 rats, testicular CYP2A1 immunoreactive protein and testosterone 7alpha-hydroxylase activity (7alpha-TOHase) exhibited a circadian variation with a daytime maximum and a night-time minimum (82.2 +/- 42.0 and 21.9 +/- 4.5 pmol 7alpha-hydroxytestosterone/min/mg protein, respectively). Caloric restriction (to 60% of ad libitum consumption), which reduces the severity of Leydig cell tumors in rats, decreased expression of both CYP2A1 and testicular 7alpha-TOHase >80% and eliminated their circadian variation. Conversely, caloric restriction induced a circadian rhythm in testicular 7-benzyloxyresorufin-O-dealkylase activity. Testicular microsomes from ad libitum-fed rats having peak diurnal 7alpha-TOHase activity had significantly greater (30%) microsome-mediated aflatoxin B1-DNA binding activity compared to microsomes prepared from nocturnal phase ad libitum-fed or calorically restricted rats which expressed low 7alpha-TOHase activity. In 12-month-old Fischer 344 rats, high CYP2A1 expression was correlated with severe Leydig cell hyperplasia (r = 0.80), whereas CYP2A immunoreactive protein and 7alpha-TOHase were expressed at lower levels in Sprague-Dawley than in Fischer 344 rats and were undetectable in pig, monkey, and human testes. These are strains/species that do not exhibit significant Leydig cell hyperplasia. This suggests that caloric intake, strain, and circadian factors may all mediate testicular CYP2A1 expression in the rat and that CYP2A1 may in turn influence carcinogen activation and pathological status in the testis.

Aflatoxin B1↗

PubMed1996

Absence of fetal liver hematopoiesis in mice deficient in transcriptional coactivator core binding factor beta.

Core binding factor beta (CBF beta) is considered to be a transcriptional coactivator that dimerizes with transcription factors core binding factor alpha 1 (CBFA1), -2, and -3, and enhances DNA binding capacity of these transcription factors. CBF beta and CBFA2, which is also called acute myeloid leukemia 1 gene, are frequently involved in chromosomal translocations in human leukemia. To elucidate the function of CBF beta, mice carrying a mutation in the Cbfb locus were generated. Homozygous mutant embryos died between embryonic days 11.5-13.5 due to hemorrhage in the central nervous system. Mutant embryos had primitive erythropoiesis in yolk sac but lacked definitive hematopoiesis in fetal liver. In the yolk sac of mutant embryos, no erythroid or myeloid progenitors of definitive hematopoietic origin were detected, and the expression of flk-2/flt-3, the marker gene for early precursor cells of definitive hematopoiesis, was absent. These data suggest that Cbfb is essential for definitive hematopoiesis in liver, especially for the commitment to early hematopoietic precursor cells.

Animals↗

PubMed1996

Targeted disruption of ATM leads to growth retardation, chromosomal fragmentation during meiosis, immune defects, and thymic lymphoma.

ATM, the gene mutated in the inherited human disease ataxia-telangiectasia, is a member of a family of kinases involved in DNA metabolism and cell-cycle checkpoint control. To help clarify the physiological roles of the ATM protein, we disrupted the ATM gene in mice through homologous recombination. Initial evaluation of the ATM knockout animals indicates that inactivation of the mouse ATM gene recreates much of the phenotype of ataxia-telangiectasia. The homozygous mutant (ATM-/-) mice are viable, growth-retarded, and infertile. The infertility of ATM-/- mice results from meiotic failure. Meiosis is arrested at the zygotene/pachytene stage of prophase I as a result of abnormal chromosomal synapsis and subsequent chromosome fragmentation. Immune defects also are evident in ATM-/- mice, including reduced numbers of B220+CD43- pre-B cells, thymocytes, and peripheral T cells, as well as functional impairment of T-cell-dependent immune responses. The cerebella of ATM-/- mice appear normal by histologic examination at 3 to 4 months and the mice have no gross behavioral abnormalities. The majority of mutant mice rapidly develop thymic lymphomas and die before 4 months of age. These findings indicate that the ATM gene product plays an essential role in a diverse group of cellular processes, including meiosis, the normal growth of somatic tissues, immune development, and tumor suppression.

Animals↗

PubMed1996

Mutations in the p53 and SCID genes cooperate in tumorigenesis.

DNA damage can cause mutations that contribute to cellular transformation and tumorigenesis. The p53 tumor suppressor acts to protect the organism from DNA damage by inducing either G1 arrest to facilitate DNA repair or by activating physiological cell death (apoptosis). Consistent with this critical function of p53, mice lacking p53 are predisposed to developing tumors, particularly lymphoma. The severe combined immune deficiency (scid) focus encodes the catalytic subunit of DNA protein kinase (DNA-PKcs), a protein complex that has a role in the cellular response to DNA damage. Cells from scid mice are hypersensitive to radiation and scid lymphocytes fail to develop from precursors because they are unable to properly join DNA-coding ends during antigen receptor gene rearrangement. We examined the combined effect of loss of p53 and loss of DNA-PKcs on lymphocyte development and tumorigenesis by generating p53-/- scid mice. Our data demonstrate that loss of p53 promotes T-cell development in scid mice but does not noticeably affect B lymphopoiesis. Moreover, scid cells are able to induce p53 protein expression and activate G1 arrest or apoptosis in response to ionizing radiation, indicating that DNA-PKcs is not essential for these responses to DNA damage. Furthermore, p53-/- scid double mutant mice develop lymphoma earlier than p53-/- littermates, demonstrating that loss of these two genes can cooperate in tumorigenesis. Collectively, these results provide evidence for an unsuspected role of p53 as a checkpoint regulator in early T-cell development and demonstrate that loss of an additional component of the cellular response to DNA damage can cooperate with loss of p53 in lymphomagenesis.

Animals↗

PubMed1996

A defect in nurturing in mice lacking the immediate early gene fosB.

Although expression of the Fos family of transcription factors is induced by environmental stimuli that trigger adaptive neuronal response, evidence that Fos family members mediate these responses is lacking. To address this issue, mice were generated with an inactivating mutation in the fosB gene. fosB mutant mice are profoundly deficient in their ability to nurture young animals but are normal with respect to other cognitive and sensory functions. The nurturing defect is likely due to the absence of FosB in the preoptic area, a region of the hypothalamus that is critical for nurturing. These observations suggest that a transcription factor controls a complex behavior by regulating a specific neuronal circuit and indicate that nurturing in mammals has a genetic component.

Animals↗

PubMed1996

Targeted disruption of p107: functional overlap between p107 and Rb.

To explore the physiological role of p107, a member of retinoblastoma gene (Rb) family, we disrupted the mouse gene by homologous recombination in embryonic stem cells. p107 homozygous mutant mice were viable, fertile, and displayed no obvious abnormalities. To investigate possible functional overlap between p107 and Rb, mice with mutations at both loci were generated. Rb+/-;p107-/- mice have a pronounced growth retardation and increased mortality rate during the first 3 weeks after birth. The Rb+/-;p107-/- pups that survive to adulthood did not show any altered tumor predisposition when compared with Rb+/- mice but developed multiple dysplastic lesions of the retina. Embryos homozygous for both Rb and p107 died at approximately 11.5 days of gestation, 2 days earlier than embryos homozygous for Rb alone. Histological examination revealed accelerated apoptosis in the liver and the central nervous system of Rb-/-;p107-/- embryos relative to Rb-/- embryos. These results provide the first in vivo evidence that p107 and Rb have overlapping functions in some tissues of the developing and adult mouse.

Actins↗

PubMed1996

Shared role of the pRB-related p130 and p107 proteins in limb development.

The p130 protein shares extensive sequence similarity with pRB, the product of the retinoblastoma gene, and is a major E2F-associated protein in quiescent cells. To investigate its biological function, we have mutated p130 via gene targeting in the mouse. Homozygous mutation of p130 had little discernible effect on development or on the growth of mouse embryo fibroblasts in culture. Much of the E2F activity that normally associates with p130 in serum-starved mouse embryo fibroblasts associated instead with the highly related p107 protein. To determine whether p130 and p107 have overlapping biological roles, we produced mice having simultaneous inactivation of the p130 and p107 genes. Such mice exhibited deregulated chondrocyte growth, defective endochondral bone development, shortened limbs, and neonatal lethality. These findings indicate that p130 and p107 play an important role in limb development through their abilities to control chondrocyte proliferation. Thus, in certain settings p107 and p130 perform growth-regulatory functions that are not fulfilled by pRB.

Animals↗

PubMed1996

Lack of evidence for neutrophil participation during infarct formation following focal cerebral ischemia in the rat.

The involvement of neutrophils in the pathogenesis of cerebral ischemic injury in two rat models of focal ischemia was investigated. In Experiment I, a model of focal ischemia with partial reperfusion was used. Although significant and discrete ischemic damage within the neocortex was nearly maximal at 12 h postocclusion, no elevation in neutrophils was seen at this time point. Even after 21 h postocclusion, only a subtle increase in neutrophils within the ischemic tissue was observed. To further investigate the possible role of neutrophils in cerebral ischemia, the effect of cyclophosphamide-induced neutropenia was investigated (Experiment II). While a marked reduction (>98%) in systemic neutrophils was achieved in advance of and during the ischemic challenge, no reduction in the volume of ischemic damage was observed. In Experiment III, variations in the rat model of focal ischemia were made to produce a larger area of ischemic damage, as well as to permit complete reperfusion of blood to the affected cortex. While more neutrophils were seen in this variation of the model, very few were observed (< 1 per field) prior to the time that maximal ischemic damage had already occurred. Together, these experiments revealed that substantial brain necrosis occurred prior to the appearance of neutrophils, under conditions of partial, as well as complete, reperfusion. Moreover, at the time points when elevations in neutrophils were observed, no further increase in volume of ischemic damage was noted. Finally, pharmacologic removal of neutrophils prior to ischemia did not alter the size of the ischemic region. These data therefore fail to support the hypothesis that neutrophils play a general and essential role in infarct formation following focal brain ischemia and argue that further studies are required to more clearly elucidate the conditions under which neutrophils might participate in ischemic pathogenesis.

Animals↗

PubMed1996

Scrambler, a new neurological mutation of the mouse with abnormalities of neuronal migration.

A novel spontaneous neurological mutation, scrambler (scm), appeared in the inbred mouse strain DC/Le (dancer) in 1991. Mice homozygous for this recessive mutation are recognized by an unstable gait and whole-body tremor. The cerebella of 30-day-old scrambler homozygotes are hypoplastic and devoid of folia; however, neither seizures nor abnormal brain wave patterns have been observed. Homozygous scrambler mutants have an ataxic gait which in the male may be a contributory factor in the failure to mate. Female homozygotes mate and breed. Life span is not reduced in either sex. Scrambler is similar to the reeler mutation in phenotype and pathology and, like reeler, probably results from defective neuronal migration. We mapped the scrambler mutation to Chromosome (Chr) 4, proving that it is distinct from the recently cloned reeler gene on Chr 5. We also determined the map position of the agrin gene, Agrn, on Chr 4, and on this basis eliminated it as a candidate for scm. Currently there is no known homology of scrambler with human lissencephalies or other human disorders caused by abnormal neuronal migration.

Agrin↗

PubMed1996

Megencephaly: a new mouse mutation on chromosome 6 that causes hypertrophy of the brain.

Megencephaly, enlarged brain, occurs in several acquired and inherited human diseases including Sotos syndrome, Robinow syndrome, Canavan's disease, and Alexander disease. This defect can be distinguished from macrocephaly, an enlarged head, which usually occurs as a consequence of congenital hydrocephalus. The pathology of megencephaly in humans has not been well defined, nor has the defect been reported to occur spontaneously in any other species. In this report we describe a recessive mutation in the mouse that results in a 25% increase in brain size in the first 8 months of life. We have determined that the megencephaly is characterized by overall hypertrophy of the brain, and not by hyperplasia of particular cell types or by hypertrophy of a singular tissue compartment. Edema and hydrocephalus are absent. This mutation has been mapped to mid-distal mouse Chromosome (Chr) 6 in a region homologous with human Chr 12.

Animals↗