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Biomedical subjects

R L Phillips

Publications and source records attributed to R L Phillips.

At least 55 records · Page 3Linked to original sources
PubMed2000

Expression of CD27 on murine hematopoietic stem and progenitor cells.

Hematopoietic stem cells (HSC) are defined by self-renewal and multilineage differentiation potentials. In order to uncover the genetic program of HSC, we utilized high-density arrays to compare gene expression in highly purified mouse HSC and their mature progeny. One molecule specifically expressed in immature cells is CD27, a member of the TNF receptor family previously shown to play roles in lymphoid proliferation, differentiation, and apoptosis. We show here that the CD27 protein is expressed by about 90% of cells in a purified HSC population. Interestingly, the CD27pos cells are enriched for cells with short-term hematopoietic activities (colony forming potential in vivo and in vitro), while the minority CD27neg population is more effective in clonal long-term transplantation.

Animals↗
PubMed2000

Production and characterization of maize chromosome 9 radiation hybrids derived from an oat-maize addition line.

In maize (Zea mays L., 2n = 2x = 20), map-based cloning and genome organization studies are often complicated because of the complexity of the genome. Maize chromosome addition lines of hexaploid cultivated oat (Avena sativa L., 2n = 6x = 42), where maize chromosomes can be individually manipulated, represent unique materials for maize genome analysis. Maize chromosome addition lines are particularly suitable for the dissection of a single maize chromosome using radiation because cultivated oat is an allohexaploid in which multiple copies of the oat basic genome provide buffering to chromosomal aberrations and other mutations. Irradiation (gamma rays at 30, 40, and 50 krad) of a monosomic maize chromosome 9 addition line produced maize chromosome 9 radiation hybrids (M9RHs)-oat lines possessing different fragments of maize chromosome 9 including intergenomic translocations and modified maize addition chromosomes with internal and terminal deletions. M9RHs with 1 to 10 radiation-induced breaks per chromosome were identified. We estimated that a panel of 100 informative M9RHs (with an average of 3 breaks per chromosome) would allow mapping at the 0. 5- to 1.0-Mb level of resolution. Because mapping with maize chromosome addition lines and radiation hybrid derivatives involves assays for the presence or absence of a given marker, monomorphic markers can be quickly and efficiently mapped to a chromosome region. Radiation hybrid derivatives also represent sources of region-specific DNA for cloning of genes or DNA markers.

Avena↗
PubMed2000

Evidence for the coincident initiation of homolog pairing and synapsis during the telomere-clustering (bouquet) stage of meiotic prophase.

To improve knowledge of the prerequisites for meiotic chromosome segregation in higher eukaryotes, we analyzed the spatial distribution of a pair of homologs before and during early meiotic prophase. Three-dimensional images of fluorescence in situ hybridization (FISH) were used to localize a single pair of homologs in diploid nuclei of a chromosome-addition line of oat, oat-maize9b. The system provided a robust assay for pairing based on cytological colocalization of FISH signals. Using a triple labeling scheme for simultaneous imaging of chromatin, telomeres and the homolog pair, we determined the timing of pairing in relation to the onset of three sequential hallmarks of early meiotic prophase: chromatin condensation (the leptotene stage), meiotic telomere clustering (the bouquet stage) and the initiation of synapsis (the zygotene stage). We found that the two homologs were mostly unpaired up through middle leptotene, at which point their spherical cloud-like domains began to transform into elongated and stretched-out domains. At late leptotene, the homologs had completely reorganized into long extended fibers, and the beginning of the bouquet stage was conspicuously marked by the de novo clustering of telomeres at the nuclear periphery. The homologs paired and synapsed during the bouquet stage, consistent with the timing of pairing observed for several oat 5S rDNA loci. In summary, results from analysis of more than 100 intact nuclei lead us to conclude that pairing and synapsis of homologous chromosomes are largely coincident processes, ruling out a role for premeiotic pairing in this system. These findings suggest that the genome-wide remodeling of chromatin and telomere-mediated nuclear reorganization are prerequisite steps to the DNA sequence-based homology-search process in higher eukaryotes.

Avena↗
PubMed2000

A maize chromosome 3 addition line of oat exhibits expression of the maize homeobox gene liguleless3 and alteration of cell fates.

Maize chromosome addition lines of oat offer the opportunity to study maize gene expression in oat and the resulting phenotypes. Morphological examination of a maize chromosome 3 addition line of oat showed that this line exhibited several morphological abnormalities including a blade-to-sheath transformation at the midrib region of the leaf, a hook-shaped panicle, and abnormal outgrowth of aerial axillary buds. Dominant mutations in the maize liguleless3 (lg3) homeobox gene result in a blade (distal)-to-sheath (proximal) transformation at the midrib region of the leaf. Ectopic expression of the dominant mutant Lg3 allele is believed to cause the phenotype. Therefore, we suspected that the maize lg3 gene, which is located on maize chromosome 3, was involved in the phenotypes observed in the maize chromosome 3 addition line of oat. Genetic analyses of an oat BC1F2 family segregating for maize chromosome 3 showed that the presence of a stable maize chromosome 3 was required for the expression of these cell fate abnormalities. RNA expression analysis of leaf sheath tissue from oat plants carrying maize chromosome 3 demonstrated that maize LG3 transcripts accumulated in oat, indicating that this expression is associated with the blade-to-sheath transformation, hook-shaped panicle and outgrowth of aerial axillary bud phenotypes. Our results demonstrate that the maize chromosome addition lines of oat are useful genetic stocks to study expression of maize genes in oat.

Avena↗
PubMed1999

Fine mapping and characterization of linked quantitative trait loci involved in the transition of the maize apical meristem from vegetative to generative structures.

Quantitative trait locus (QTL) mapping has detected two linked QTL in the 8L chromosome arm segment introgressed from Gaspé Flint (a Northern Flint open-pollinated population) into the background of N28 (a Corn Belt Dent inbred line). Homozygous recombinant lines, with a variable length of the introgressed segment, confirmed the presence of the two previously identified, linked QTL. In the N28 background, Gaspé Flint QTL alleles at both loci induce a reduction in node number, height, and days to anthesis (pollen shed). Given the determinate growth pattern of maize, the phenotypic effects indicate that the two QTL are involved in the transition of the apical meristem from vegetative to generative structures. Relative to the effects of the two QTL in the background of N28, we distinguish two general developmental factors affecting the timing of pollen shed. The primary factor is the timing of the transition of the apical meristem. The second, derivative factor is the global extent of internode elongation. Having separated the two linked QTL, we have laid the foundation for the positional cloning of the QTL with a larger effect.

Analysis of Variance↗
PubMed1999

Resurfacing of the glenoid in total shoulder arthroplasty. A comparison, at a mean of five years, of prostheses inserted with and without cement.

BACKGROUND: Clinically evident loosening of a glenoid component inserted with cement in total shoulder arthroplasty is infrequent, but radiographic changes that indicate loosening at the implant-bone interface are common and have been associated with functional limitation. We compared the results of total shoulder arthroplasties in which the glenoid implant had been inserted with cement with those of arthroplasties in which a bone-ingrowth glenoid implant had been inserted without cement. METHODS: The results of eighty-six consecutive total shoulder arthroplasties, performed by the same surgeon, were retrospectively reviewed between four and seven years after the operation. Fifty-eight shoulders in which the primary glenoid implant was in situ were assessed with use of the Simple Shoulder Test and Short Form-36 questionnaires, clinical examination, and fluoroscopic imaging of the glenoid implant-bone interface. Thirty-two of the glenoid components had been fixed with cement and twenty-six, without cement. RESULTS: Complications occurred in 16 percent (fourteen) of the eighty-six shoulders, and 9 percent (eight) of the shoulders needed a revision operation. None of the revisions were done because of loosening of the glenoid component. Five of the eight revisions involved implants that had been inserted without cement. Three of these implants were revised because of early instability and two, because the polyethylene component had separated from the metal tray of the glenoid implant. With the numbers available, we could not detect any significant differences between the groups with respect to pain, range of motion, function of the shoulder, or general health. Radiographic analysis demonstrated a high level of interobserver agreement (kappa = 0.89). Radiolucent lines were observed after 41 percent (thirteen) of the thirty-two arthroplasties performed with cement compared with 23 percent (six) of the twenty-six arthroplasties performed without cement. The proportion of implants classified as probably loose was approximately three times greater in the group in which cement had been used. Eccentric wear of the posterior rim of the metal tray and focal osteolysis under the metal tray were observed in the group in which the component had been inserted without cement; these findings may indicate a potential for progression of radiographic loosening with increased durations of follow-up. CONCLUSIONS: We concluded that, despite the higher rate of early complications, the intermediate-term outcomes of arthroplasties in which the glenoid implant is inserted without cement are comparable with those of arthroplasties with cementing of the glenoid component.

Adult↗
PubMed1998

Chromosome-specific molecular organization of maize (Zea mays L.) centromeric regions.

A set of oat-maize chromosome addition lines with individual maize (Zea mays L.) chromosomes present in plants with a complete oat (Avena sativa L.) chromosome complement provides a unique opportunity to analyze the organization of centromeric regions of each maize chromosome. A DNA sequence, MCS1a, described previously as a maize centromere-associated sequence, was used as a probe to isolate cosmid clones from a genomic library made of DNA purified from a maize chromosome 9 addition line. Analysis of six cosmid clones containing centromeric DNA segments revealed a complex organization. The MCS1a sequence was found to comprise a portion of the long terminal repeats of a retrotransposon-like repeated element, termed CentA. Two of the six cosmid clones contained regions composed of a newly identified family of tandem repeats, termed CentC. Copies of CentA and tandem arrays of CentC are interspersed with other repetitive elements, including the previously identified maize retroelements Huck and Prem2. Fluorescence in situ hybridization revealed that CentC and CentA elements are limited to the centromeric region of each maize chromosome. The retroelements Huck and Prem2 are dispersed along all maize chromosomes, although Huck elements are present in an increased concentration around centromeric regions. Significant variation in the size of the blocks of CentC and in the copy number of CentA elements, as well as restriction fragment length variations were detected within the centromeric region of each maize chromosome studied. The different proportions and arrangements of these elements and likely others provide each centromeric region with a unique overall structure.

Base Sequence↗
PubMed1998

A knob-associated tandem repeat in maize capable of forming fold-back DNA segments: are chromosome knobs megatransposons?

A class of tandemly repeated DNA sequences (TR-1) of 350-bp unit length was isolated from the knob DNA of chromosome 9 of Zea mays L. Comparative fluorescence in situ hybridization revealed that TR-1 elements are also present in cytologically detectable knobs on other maize chromosomes in different proportions relative to the previously described 180-bp repeats. At least one knob on chromosome 4 is composed predominantly of the TR-1 repeat. In addition, several small clusters of the TR-1 and 180-bp repeats have been found in different chromosomes, some not located in obvious knob heterochromatin. Variation in restriction fragment fingerprints and copy number of the TR-1 elements was found among maize lines and among maize chromosomes. TR-1 tandem arrays up to 70 kilobases in length can be interspersed with stretches of 180-bp tandem repeat arrays. DNA sequence analysis and restriction mapping of one particular stretch of tandemly arranged TR-1 units indicate that these elements may be organized in the form of fold-back DNA segments. The TR-1 repeat shares two short segments of homology with the 180-bp repeat. The longest of these segments (31 bp; 64% identity) corresponds to the conserved region among 180-bp repeats. The polymorphism and complex structure of knob DNA suggest that, similar to the fold-back DNA-containing giant transposons in Drosophila, maize knob DNA may have some properties of transposable elements.

Base Sequence↗
PubMed1998

Complex structure of knob DNA on maize chromosome 9. Retrotransposon invasion into heterochromatin.

The recovery of maize (Zea mays L.) chromosome addition lines of oat (Avena sativa L.) from oat x maize crosses enables us to analyze the structure and composition of specific regions, such as knobs, of individual maize chromosomes. A DNA hybridization blot panel of eight individual maize chromosome addition lines revealed that 180-bp repeats found in knobs are present in each of these maize chromosomes, but the copy number varies from approximately 100 to 25, 000. Cosmid clones with knob DNA segments were isolated from a genomic library of an oat-maize chromosome 9 addition line with the help of the 180-bp knob-associated repeated DNA sequence used as a probe. Cloned knob DNA segments revealed a complex organization in which blocks of tandemly arranged 180-bp repeating units are interrupted by insertions of other repeated DNA sequences, mostly represented by individual full size copies of retrotransposable elements. There is an obvious preference for the integration of retrotransposable elements into certain sites (hot spots) of the 180-bp repeat. Sequence microheterogeneity including point mutations and duplications was found in copies of 180-bp repeats. The 180-bp repeats within an array all had the same polarity. Restriction maps constructed for 23 cloned knob DNA fragments revealed the positions of polymorphic sites and sites of integration of insertion elements. Discovery of the interspersion of retrotransposable elements among blocks of tandem repeats in maize and some other organisms suggests that this pattern may be basic to heterochromatin organization for eukaryotes.

Avena↗
PubMed1998

Age-related changes in brain glucose metabolism in adults with attention-deficit/hyperactivity disorder and control subjects.

Using positron emission tomography and [18F]-2-fluoro-2-deoxy-D-glucose, the authors determined cerebral metabolic rates for glucose (CMRglc) in 39 adults (18-51 years old) with attention-deficit/hyperactivity disorder (ADHD) and 56 healthy control adults (19-56 years old) during the performance of a continuous attention task. Increased age was associated with reduced global CMRglc in ADHD women, but not in ADHD men, control men, or control women. Better performance on the attention task was significantly associated with increased age only in the ADHD female group. Determining the role of behavioral, hormonal, and genetic factors is a challenge for future research.

Adolescent↗
PubMed1997

Oat-maize chromosome addition lines: a new system for mapping the maize genome.

Novel plants with individual maize chromosomes added to a complete oat genome have been recovered via embryo rescue from oat (Avena sativa L., 2n = 6x = 42) x maize (Zea mays L., 2n = 20) crosses. An oat-maize disomic addition line possessing 21 pairs of oat chromosomes and one maize chromosome 9 pair was used to construct a cosmid library. A multiprobe (mixture of labeled fragments used as a probe) of highly repetitive maize-specific sequences was used to selectively isolate cosmid clones containing maize genomic DNA. Hybridization of individual maize cosmid clones or their subcloned fragments to maize and oat genomic DNA revealed that most high, middle, or low copy number DNA sequences are maize-specific. Such DNA markers allow the identification of maize genomic DNA in an oat genomic background. Chimeric cosmid clones were not found; apparently, significant exchanges of genetic material had not occurred between the maize-addition chromosome and the oat genome in these novel plants or in the cloning process. About 95% of clones selected at random from a maize genomic cosmid library could be detected by the multiprobe. The ability to selectively detect maize sequences in an oat background enables us to consider oat as a host for the cloning of specific maize chromosomes or maize chromosome segments. Introgressing maize chromosome segments into the oat genome via irradiation should allow the construction of a library of overlapping fragments for each maize chromosome to be used for developing a physical map of the maize genome.

Chromosome Mapping↗
PubMed1997

Cerebral glucose utilization is reduced in second test session.

Cerebral glucose utilization was higher during the first positron emission tomography (PET) session than during the second session, as assayed using the PET [18F]fluorodeoxyglucose method in male human volunteers. This difference was due largely to data from subjects with low-trait anxiety, since subjects with high anxiety showed similar metabolism in both PET sessions. High-anxiety subjects showed greater right/ left ratios of cerebral metabolism than low-anxiety subjects, particularly during the second PET session. These findings suggest that the level of anxiety may be an important variable to consider in PET studies using multiple sessions.

Adult↗
PubMed1997

Aneuploid marker assignment in hexaploid oat with the C genome as a reference for determining remnant homoeology.

Nullisomic lines of hexaploid oat Avena sativa L. (2n = 6x - 2 = 40, AACCDD) cultivar Sun II were used to assign 134 DNA sequences to 10 chromosome-associated syntenic groups. A limited set of ditelosomic lines allowed localization of subsets of these sequences to six chromosome arms. Advantages of using such aneuploids in mapping are in the assignment of gene families, monomorphic RFLP sequences, and oat linkage groups to chromosomes. The published hexaploid oat RFLP linkage map has 38 linkage groups, 17 more than expected on the basis of the haploid chromosome number. Using nullisomics, eight linkage groups were assigned to five physical chromosomes; using ditelosomics, three of these linkage groups were assigned to their respective chromosome arms. The A- and D-genome chromosome sets of oat are indistinguishable from each other based on different staining and genomic in situ hybridization techniques, while C-genome chromosomes are distinct. Because chromosomal rearrangements such as translocations and inversions have played an important role in the evolution of hexaploid oat, the distinction of C-genome chromosomes can be used to determine remnant homoeologous segments that exist in the other two genomes. Among the 10 syntenic groups identified, six chromosomes showed sequence homoeology believed to represent segmental homoeologous regions. Owing to various evolutionary forces, segmental homoeology instead of whole chromosome homoeology appears to best describe the genome organization in hexaploid oat.

Aneuploidy↗