PubMed Health⌕ Search

Biomedical subjects

Roger H Reeves

Publications and source records attributed to Roger H Reeves.

At least 19 recordsLinked to original sources
PubMed2006

Hippocampal hypocellularity in the Ts65Dn mouse originates early in development.

Ts65Dn, a well-characterized animal model for Down syndrome, has three copies of the distal end of mouse chromosome 16 and therefore has segmental trisomy for orthologs for nearly half of the genes located on human chromosome 21. Ts65Dn mice have learning and memory impairments, especially in tasks involving the hippocampus. Previous studies have shown that older adult Ts65Dn mice have structural abnormalities in the hippocampus including fewer granule cells in dentate gyrus and more pyramidal cells in the CA3 subfield of cornus ammonis. However, it is not clear whether those changes are secondary to the age-related neurodegeneration of the basal forebrain cholinergic neurons that project to the hippocampus or if they originate earlier during hippocampal development. To address this question, we performed a quantitative study of the hippocampal volume and the numbers of granule cell and pyramidal neurons in young (postnatal day 6, P6) and adult (3-month-old) mice using the optical fractionator method. At P6, Ts65Dn mice had 20% fewer granule cells in dentate gyrus than did euploid littermates. Similarly, compared to euploid, P6 trisomic mice showed an 18% reduction in mitotic cells in the granule cell layer and the hilus, where granule cell precursors divide to generate the internal granule cell layer. Granule cell hypocellularity persists in 3-month-old Ts65Dn mice before the onset of cholinergic atrophy. The hypocellularity seen in the trisomic adult hippocampus originates early in development and may contribute to specific cognitive deficits in these mice.

Age Factors↗
PubMed2006

Down syndrome mouse models are looking up.

A new mouse model of Down syndrome (DS) carries a copy of human chromosome 21 (Hsa21), in addition to a full complement of mouse chromosomes. In terms of the number of trisomic genes represented, this model, known as 'Tc1', is closer to the genetic background of DS than any previous model. The Tc1 model not only recapitulates several of the DS features present in other mouse models but also exhibits heart defects that are similar to those that make trisomy 21 the leading cause of congenital heart disease in humans. Many cells in adult Tc1 mice show mosaicism - that is, the Hsa21 is lost from some cells during development - increasing the complexity of analyses using this model. Tc1 mice provide a powerful tool for investigation of the pathogenesis of trisomy 21, and a platform for analysis of similarities and differences in the evolution of gene regulation.

Animals↗
PubMed2006

A quantitative trait loci analysis to map genes involved in lipopolysaccharide-induced inflammatory response: identification of macrophage scavenger receptor 1 as a candidate gene.

Septic shock, which is a major complication observed after trauma and other human diseases, is likely the product of a prolonged and poorly controlled systemic inflammatory response. Symptoms of sepsis can be partially reproduced by injection of bacterial LPS in mice. Differences in mortality between C57BL/6J(high) and A/J(low) mice after LPS injection have been previously observed and correlated with differences in the inflammatory response between these two inbred strains. In the present study, we have mapped four loci responsible for differences in levels of LPS-induced IL-10, named modifier of IL-10, between the two strains. A locus within mouse chromosome 8 was confirmed using chromosome 8 consomic mice. This locus was further reduced in size by haplotype analysis and evaluated by the presence of potential candidate genes. The macrophage scavenger receptor 1 (Msr1) within this locus emerged as a candidate gene based on differences at the expression and structural levels between C57BL/6J and A/J mice. In comparison with wild-type (C57BL/6J) mice, Msr1 knockout mice displayed reduced levels of LPS-induced IL-10, but not of TNF-alpha or IL-6, confirming a specific role for this gene in the regulation of IL-10. These results suggest that Msr1 is involved in the regulation of the anti-inflammatory process, thus offering a new perspective on the molecular mechanisms involved in endotoxemia and sepsis.

Animals↗
PubMed2006

Defective cerebellar response to mitogenic Hedgehog signaling in Down [corrected] syndrome mice.

Trisomy 21 is the cause of Down [corrected] syndrome (DS) which is characterized by a number of phenotypes, including a brain which is small and hypocellular compared to that of euploid individuals. The cerebellum is disproportionately reduced. Ts65Dn mice are trisomic for orthologs of about half of the genes on human chromosome 21 and provide a genetic model for DS. These mice display a number of developmental anomalies analogous to those in DS, including a small cerebellum with a significantly decreased number of both granule and Purkinje cell neurons. Here we trace the origin of the granule cell deficit to precursors in early postnatal development, which show a substantially reduced mitogenic response to Hedgehog protein signaling. Purified cultures of trisomic granule cell precursors show a reduced but dose-dependent response to the Sonic hedgehog protein signal in vitro, demonstrating that this is a cell-autonomous deficit. Systemic treatment of newborn trisomic mice with a small molecule agonist of Hedgehog pathway activity increases mitosis and restores granule cell precursor populations in vivo. These results demonstrate a basis for and a potential therapeutic approach to a fundamental aspect of CNS pathology in DS.

Aneuploidy↗
PubMed2006

Understanding the basis for Down syndrome phenotypes.

Down syndrome is a collection of features that are caused by trisomy for human Chromosome 21. While elevated transcript levels of the more than 350 genes on the chromosome are primarily responsible, it is likely that multiple genetic mechanisms underlie the numerous ways in which development and function diverge in individuals with trisomy 21 compared to euploid individuals. We consider genotype-phenotype interactions with the goal of producing working concepts that will be useful for approaches to ameliorate the effects of trisomy.

Alleles↗
PubMed2005

Perinatal loss of Ts65Dn Down syndrome mice.

Ts65Dn mice inherit a marker chromosome, T(17(16))65Dn, producing segmental trisomy for orthologs of about half of the genes on human chromosome 21. These mice display a number of phenotypes that are directly comparable to those in humans with trisomy 21 and are the most widely used animal model of Down syndrome (DS). However, the husbandry of Ts65Dn mice is complicated. Males are sterile, and only 20-40% of the offspring of Ts65Dn mothers are trisomic at weaning. The lower-than-expected frequency of trisomic offspring has been attributed to losses at meiosis, during gestation and at postnatal stages, but no systematic studies support any of these suppositions. We show that the T(17(16))65Dn marker chromosome is inherited at expected frequency and is fully compatible with development to midgestation. Disproportional loss of trisomic offspring occurs in late gestation and continues through birth to weaning. Different maternal H2 haplotypes are significantly associated with the frequency of trisomy at weaning in patterns different from those reported previously. The proportion of trisomic mice per litter decreases with age of the Ts65Dn mother. These results provide the first statistical and numerical evidence supporting the prenatal and perinatal pattern of loss in the Ts65Dn mouse model of DS.

Animals↗
PubMed2005

IL-10 plasma levels are elevated after LPS injection in splenectomized A/J mice.

BACKGROUND: Splenectomy is clinically indicated in certain cases of hypersplenism and splenic trauma. However, it is associated with serious complications, in particular, reduced clearance of encapsulated organisms and a high incidence of sepsis, which has been coined overwhelming post-splenectomy sepsis (OPSS). In addition to the role of the spleen in the clearance of microorganisms, this organ may be involved in regulation of the inflammatory response. We investigated the effect of splenectomy on the inflammatory process induced by LPS in a murine model that resembles, in part, the pathophysiological aspects of sepsis. MATERIALS AND METHODS: Male mice (8-weeks-old) from different inbred strains were randomized into three groups: splenectomized (SPX), sham operated (SHAM), and non-operated controls (NoOp). After 9 days of recovery, mice were injected with LPS (15 mg/kg) and cytokine plasma levels were measured by ELISA at 1.5 or 6 h after injection. Peritoneal macrophages (PMphi) were isolated from the three groups, and cytokine production was evaluated after incubation with LPS in culture conditions. RESULTS: IL-10 plasma levels were elevated in SPX A/J mice (6.7 +/- 0.4 mug/ml) after injection of LPS (15 mg/kg) compared to NoOp A/J mice (4.2 +/- 0.2 mug/ml, P < 0.05). Similar elevation in IL-10 plasma levels was detected in SPX DBA/2J mice as compared to NoOp DBA/2J mice, but not in C57BL/6J and BALB/cJ mice. In contrast, SPX AKR mice displayed lower IL-10 levels than NoOp mice. PMphis from SPX A/J mice produced elevated levels of IL-10 compared to PMphis from SHAM or NoOp A/J mice, mimicking the in vivo observations. CONCLUSION: Our data suggest that the spleen plays an important role in modulating the inflammatory process induced by LPS, extending beyond passive clearance of encapsulated organisms. In addition, the contribution of the spleen to the inflammatory process may be influenced by the genetic background.

Animals↗
PubMed2005

Tumor suppressor in lung cancer 1 (TSLC1) alters tumorigenic growth properties and gene expression.

BACKGROUND: Introduction of cDNA or genomic clones of the tumor suppressor in lung cancer 1 (TSLC1) gene into the non-small cell lung cancer line, A549, reverses tumorigenic growth properties of these cells. These results and the observation that TSLC1 is down-regulated in a number of tumors suggest that TSLC1 functions as a critical switch mediating repression of tumorigenesis. RESULTS: To investigate this mechanism, we compared growth properties of A549 with the TSLC1-containing derivative. We found a G1/S phase transition delay in 12.2. Subtractive hybridization, quantitative PCR, and TranSignal Protein/DNA arrays were used to identify genes whose expression changed when TSLC1 was up-regulated. Members of common G1/S phase regulatory pathways such as TP53, MYC, RB1 and HRAS were not differentially expressed, indicating that TSLC1 may function through an alternative pathway(s). A number of genes involved in cell proliferation and tumorigenesis were differentially expressed, notably genes in the Ras-induced senescence pathway. We examined expression of several of these key genes in human tumors and normal lung tissue, and found similar changes in expression, validating the physiological relevance of the A549 and 12.2 cell lines. CONCLUSION: Gene expression and cell cycle differences provide insights into potential downstream pathways of TSLC1 that mediate the suppression of tumor properties in A549 cells.

Carcinoma, Non-Small-Cell Lung↗
PubMed2005

Long-range chromosomal engineering is more efficient in vitro than in vivo.

Cre/LoxP mediated chromosomal engineering in embryonic stem (ES) cells has a variety of applications, including the creation of model systems for studying aneuploidy. Targeted meiotic recombination (TAMERE) was proposed as a high efficiency in vivo alternative to effect Cre-mediated recombination, in which Cre recombinase under control of the Synaptonemal Complex 1 promoter is expressed during male meiosis in transgenic mice. TAMERE has been successfully used with LoxP sites up to 100 kb apart. We tested TAMERE for a chromosome engineering application in which LoxP sequences were integrated into sites 3.9 Mb apart on the same (cis) or opposite (trans) copies of mouse Chromosome 16 (MMU16). TAMERE was ineffective in generating either a deletion or a translocation in vivo. The TAMERE method may be of limited use for large genomic rearrangements. The desired translocation was achieved with an in vitro method that can be used in any ES cell line. Mice produced from the reciprocal duplication/deletion of MMU16 in a region homologous to human chromosome 21 provide models that are useful in studies of Down syndrome.

Animals↗
PubMed2005

Genetic determinants influencing the response to injury, inflammation, and sepsis.

The genetic background has recently been recognized as an important element in the response to injury, contributing to the variability in the clinical outcome of critically ill patients. The traditional approach to studying the genetic contribution requires the availability of families with multiple members who have experienced similar disease conditions, a situation that is nearly impossible to find in the case of trauma. Association studies looking at unrelated individuals across populations require large economic and labor-intensive efforts. Thus, a candidate gene approach has been the sole methodology used to correlate genetic variability with clinical outcome. However, this approach cannot provide a comprehensive description of a multigenic condition. Animal models are an alternative for studying the genetic contributions to variability in the response to injury. A murine model is ideal because a large set of inbred strains are available; congenic, consomic, transgenic, and recombinant strains can also be used. Employing this paradigm, we have demonstrated that the response to several stressors, such as injection of E. coli lipopolysaccharide (LPS) and polymicrobial sepsis induced by cecal ligation and puncture (CLP), is modified by the genetic background. The inflammatory response in mice has also been shown to be affected by sex, age, and other, nongenetic components such as diet. We have exploited the differences in response among various inbred mouse strains to map loci contributing to the inflammatory response. Fine mapping strategies allow the refinement of sets of candidate genes, which can be identified by positional cloning. Detection of genetic variation affecting the inflammatory response in murine models provides a basis for determining whether polymorphisms in orthologous human genes correlate with particular clinical outcomes from injury. Thus, discovery of these genes could impact patient care by acting as markers of a specific predisposition in humans.

Age Factors↗
PubMed2005

Protection from lethal endotoxic shock after testosterone depletion is linked to chromosome X.

Men are considered more susceptible to sepsis after severe injury than are women, which has been attributed to a suppressing effect of male sex steroids on the inflammatory response. Moreover, the effect of sex steroids on the inflammatory process depends on the genetic background. The present study examined the genetic contribution to survival after endotoxic shock in mice depleted of testosterone by surgical castration. Six-week-old male mice, from strains A/J, AKR/J, C57BL/6J (B6), BALBc/J, DBA/2J, and C3H/HeN, were castrated (CX) or nonoperated (NoOp). Two weeks after surgery, mice were injected intraperitoneally with Escherichia coli lipopolysaccharide (15 mg/kg) and the frequency of mortality was monitored. CX A/J mice showed a significantly higher survival rate than NoOp mice, but this protective effect was not observed in the other strains. Administration of 5-alpha-dihydrotestosterone to CX A/J mice reverted the protection by CX. The protective effect of CX was also observed in crosses of female A/J and male B6 (AXB), but not female B6 and male A/J (BXA), suggesting that protection is linked to the A/J X chromosome. This possibility was corroborated by using consomic mice containing A/J chromosome X and the remaining chromosomes from B6. These results suggest that testosterone is a negative factor in the recovery from endotoxic shock, depending on the genetic background.

Animals↗
PubMed2004

The Collaborative Cross, a community resource for the genetic analysis of complex traits.

The goal of the Complex Trait Consortium is to promote the development of resources that can be used to understand, treat and ultimately prevent pervasive human diseases. Existing and proposed mouse resources that are optimized to study the actions of isolated genetic loci on a fixed background are less effective for studying intact polygenic networks and interactions among genes, environments, pathogens and other factors. The Collaborative Cross will provide a common reference panel specifically designed for the integrative analysis of complex systems and will change the way we approach human health and disease.

Animals↗
PubMed2004

Transcript level alterations reflect gene dosage effects across multiple tissues in a mouse model of down syndrome.

Human trisomy 21, which results in Down syndrome (DS), is one of the most complicated congenital genetic anomalies compatible with life, yet little is known about the molecular basis of DS. It is generally accepted that chromosome 21 (Chr21) transcripts are overexpressed by about 50% in cells with an extra copy of this chromosome. However, this assumption is difficult to test in humans due to limited access to tissues, and direct support for this idea is available for only a few Chr21 genes or in a limited number of tissues. The Ts65Dn mouse is widely used as a model for studies of DS because it is at dosage imbalance for the orthologs of about half of the 284 Chr21 genes. Ts65Dn mice have several features that directly parallel developmental anomalies of DS. Here we compared the expression of 136 mouse orthologs of Chr21 genes in nine tissues of the trisomic and euploid mice. Nearly all of the 77 genes which are at dosage imbalance in Ts65Dn showed increased transcript levels in the tested tissues, providing direct support for a simple model of increased transcription proportional to the gene copy number. However, several genes escaped this rule, suggesting that they may be controlled by additional tissue-specific regulatory mechanisms revealed in the trisomic situation.

Animals↗
PubMed2003

Protection from doxorubicin-induced cardiac toxicity in mice with a null allele of carbonyl reductase 1.

Doxorubicin is a highly effective antineoplastic agent, but it can produce the serious side effects of acute cardiac injury and chronic congestive heart failure. Carbonyl reductase (CBR) has been implicated in the development of doxorubicin-induced cardiotoxicity. To test whether a decrease in CBR levels was protective against doxorubicin toxicity, we created a null allele of the Cbr1 gene. Mice with one functional copy of the gene (Cbr1 +/-) were healthy and grossly normal despite having decreased levels of Cbr1 transcript and protein. Control and Cbr1 +/- mice were administered doxorubicin at 20 mg/kg i.p. Cbr1 +/- mice showed decreased circulating levels of the cardiotoxic metabolite, doxorubicinol, after administration. Within 2 weeks, 91% of wild-type mice were severely affected (n = 11) compared with 18% of Cbr1 +/- mice (n = 11). Echocardiography and histological analysis showed that Cbr1 +/- mice were protected from gross and cellular level pathologies associated with doxorubicin treatment. Demonstration that inhibition of carbonyl reductase blocks the toxic effects on the heart has important implications for improving the use of doxorubicin in chemotherapy.

Alcohol Oxidoreductases↗
PubMed2003

Global disruption of the cerebellar transcriptome in a Down syndrome mouse model.

Trisomy 21 (Down syndrome) results in cerebellar dysmorphology with direct parallels in the Ts65Dn mouse. Despite pronounced changes in morphology, cerebellar function is not markedly different. As a first test of whether those cerebellar cells that have survived to adulthood in trisomic mice are equivalent to euploid cells, we used microarrays to assess the trisomic and euploid cerebella. Trisomic and euploid transcriptomes were robustly distinguished. Changes in expression of individual genes were very subtle, but the differences in respective transcriptome phenotypes extended deeply into the set of nearly 7000 probes (genes) located throughout the genome. In contrast to deterministic models of gene action in trisomy, examination of the discriminating genes in two independent experiments suggests that the global perturbation includes a significant stochastic component. Thus, dosage imbalance of 124 genes in Ts65Dn mice alters the expression of thousands of genes to create a variable trisomic transcriptome. This global destabilization has important implications for approaches to ameliorative therapies in Down syndrome.

Animals↗
PubMed2002

Craniofacial phenotypes in segmentally trisomic mouse models for Down syndrome.

Trisomy for chromosome 21 (Chr 21) has profound effects on development that result in a constellation of phenotypes known as Down syndrome (DS). Distinctive craniofacial manifestations are among the few features common to all individuals with DS. The characteristic face of a person with DS results primarily from maldevelopment of the underlying craniofacial skeleton. The Ts65Dn mouse, which has segmental trisomy 16, producing dosage imbalance for about half the genes found on human Chr 21, exhibits specific skeletal malformations corresponding directly to the craniofacial dysmorphogenesis in DS. Here we demonstrate that Ts1Cje mice, which are at dosage imbalance for about 3/4 of the genes triplicated in Ts65Dn, demonstrate a very similar pattern of anomalies in the craniofacial skeleton. However, one characteristic of Ts65Dn mice, a broadening of the cranial vault contributing to brachycephaly, is not seen in Ts1Cje mice. These observations independently confirm that a dosage imbalance for mouse genes orthologous to those on human Chr 21 has corresponding effects in both species. The subtle differences in the craniofacial phenotypes of Ts1Cje and Ts65Dn mice have implications for elucidation of the mechanisms by which this aneuploidy disrupts development.

Animals↗
PubMed2002

Genetic and comparative mapping of genes dysregulated in mouse hearts lacking the Hand2 transcription factor gene.

The helix-loop-helix transcription factor HAND2 plays a vital role in the development of the heart, limb, facies, and other neural crest-derived structures. We used differential display analysis to identify 33 putative HAND2-regulated ESTs that are differentially expressed in Hand2(-/-) vs wild-type mice. We determined the positions on mouse and human genetic maps of 29 of these by using the T31 mouse Radiation Hybrid panel, comparison to human genomic sequence, and comparative mapping. We examined the conserved chromosomal locations for phenotypes that involve development of heart, face, and limb structures that are affected by HAND2. One EST mapped to a region of conserved synteny between mouse chromosome 2 and human chromosome 10p. RACE analysis extended the sequence and identified this cDNA as the mouse ortholog of human nebulette, an actin-binding protein expressed in fetal heart. Nebulette was shown to be deleted in DiGeorge Syndrome 2 patients with the proximal deletion of human 10p13-p14 that is associated with cardiac and craniofacial abnormalities.

Animals↗