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Biomedical subjects

David L Nelson

Publications and source records attributed to David L Nelson.

At least 55 records · Page 3Linked to original sources
PubMed2002

Inheritance of acylsugar contents in tomatoes derived from an interspecific cross with the wild tomato Lycopersicon pennellii and their effect on spider mite repellence.

Acylsugars present in Lycopersicon pennellii are responsible for the high levels of pest resistance often found in this wild tomato taxon. We investigated the inheritance of acylsugar contents in segregating populations of the interspecific tomato cross L. esculentum x L. pennellii and estimated correlations between leaflet acylsugar contents and the levels of mite repellence. Acylsugar contents were quantified with the Sommogy-Nelson colorimetric method in the acessions L. esculentum 'TOM-584' (P(1), low acylsugars), L. pennellii 'LA-716' (P(2), high acylsugars), in the interspecific F(1) (P(1) x P(2)) and in the F(2 )(P(1) x P(2)) generations. Mite resistance was assessed by a repellence test. Broad-sense heritability of acylsugar contents was moderately high (h(2)(b) = 0.476). Frequency distributions in the P(1), P(2), F(1) and F(2) can be explained by the action of a single major locus, with near-complete dominance of the L. esculentum allele for low-acylsugar content over the L. pennellii allele for high content. Indirect selection for high levels of acylsugars in leaflets led to correlated increases in the levels of mite repellency, indicating that acylsugars may be the main factor involved in mite resistance.

Animals↗
PubMed2002

Drosophila fragile X protein, DFXR, regulates neuronal morphology and function in the brain.

Mental retardation is a pervasive societal problem, 25 times more common than blindness for example. Fragile X syndrome, the most common form of inherited mental retardation, is caused by mutations in the FMR1 gene. Fragile X patients display neurite morphology defects in the brain, suggesting that this may be the basis of their mental retardation. Drosophila contains a single homolog of FMR1, dfxr (also called dfmr1). We analyzed the role of dfxr in neurite development in three distinct neuronal classes. We find that DFXR is required for normal neurite extension, guidance, and branching. dfxr mutants also display strong eclosion failure and circadian rhythm defects. Interestingly, distinct neuronal cell types show different phenotypes, suggesting that dfxr differentially regulates diverse targets in the brain.

Amino Acid Sequence↗
PubMed2002

Retrovirus-mediated WASP gene transfer corrects Wiskott-Aldrich syndrome T-cell dysfunction.

The Wiskott-Aldrich syndrome (WAS) is an X-linked disorder characterized by thrombocytopenia, eczema, and immunodeficiency. At present, the only definitive therapy for the disease is allogeneic bone marrow transplantation (BMT). Because of the frequent lack of suitable donors and the potential severe complications associated with BMT, the development of gene-based therapeutic strategies for WAS is highly desirable. To study whether corrective gene transfer into WAS T cells can lead to restoration of the immunologic defects of WAS, a retroviral vector expressing the WAS protein (WASP) gene was used to transduce human T-lymphotropic virus type 1-transformed T-cell lines and primary T lymphocytes from patients with WAS. After transduction, WAS T cells showed levels of WASP expression similar to those found in cells from normal individuals. In addition, the reconstituted WASP interacted in vitro with proteins containing SH3 domain such as Grb2, PLC-gamma1, and Fyn, each of which are connected to signaling pathways linked to the actin cytoskeleton. Furthermore, after CD3 cross-linking, transduced WAS T lines showed improvement of actin polymerization and T-cell receptor/CD3 down-regulation. More importantly, primary WAS T lymphocytes transduced with WASP acquired the ability to proliferate in response to anti-CD3 stimulation. These findings suggest that biologic defects of WAS T cells can be corrected in vitro by retrovirus-mediated gene transfer and pose the basis for future investigation of gene therapy as treatment for WAS.

Actins↗
PubMed2002

Ca(2+)-binding proteins of cilia and infraciliary lattice of Paramecium tetraurelia: their phosphorylation by purified endogenous Ca(2+)-dependent protein kinases.

We purified two small, acidic calcium-binding proteins (Paramecium Ca(2+)-binding proteins, PCBP-25alpha and PCBP-25beta) from Paramecium tetraurelia by Ca(2+)-dependent chromatography on phenyl-Sepharose and by anion-exchange chromatography. The proteins were immunologically distinct. Monoclonal antibodies against PCBP-25beta did not react with PCBP-25alpha, and antibodies against centrin from Chlamydomonas reacted with PCBP-25alpha but not with PCBP-25beta. Like the centrins described previously, both PCBPs were associated with the infraciliary lattice (ICL), a fibrillar cytoskeletal element in Paramecium. Both were also present in isolated cilia, from which they could be released (with dynein) by a high-salt wash, and both PCBPs cosedimented with dynein in a sucrose gradient. PCBP-25beta was especially prominent in cilia and in the deciliation supernatant, a soluble fraction released during the process of deciliation. The results of immunoreactivity and localization experiments suggest that PCBP-25alpha is a Paramecium centrin and that PCBP-25beta is a distinct Ca(2+)-binding protein that confers Ca(2+) sensitivity on some component of the cilium, ciliary basal body or ICL. We characterized these proteins and Paramecium calmodulin as substrates for two Ca(2+)-dependent protein kinases purified from Paramecium. PCBP-25alpha and calmodulin were in vitro substrates for one of the two Ca(2+)-dependent protein kinases (CaPK-2), but only PCBP-25alpha was phosphorylated by CaPK-1. These results raise the possibility that the biological activities of PCBP-25alpha and calmodulin are regulated by phosphorylation.

Animals↗
PubMed2002

Impaired conditioned fear and enhanced long-term potentiation in Fmr2 knock-out mice.

FRAXE mental retardation results from expansion and methylation of a CCG trinucleotide repeat located in exon 1 of the X-linked FMR2 gene, which results in transcriptional silencing. The product of FMR2 is a member of a family of proteins rich in serine and proline, members of which have been associated with transcriptional activation. We have developed a murine Fmr2 gene knock-out model by replacing a fragment containing parts of exon 1 and intron 1 with the Escherichia coli lacZ gene, placing lacZ under control of the Fmr2 promoter. Expression of lacZ in the knock-out animals indicates that Fmr2 is expressed in several tissues, including brain, bone, cartilage, hair follicles, lung, tongue, tendons, salivary glands, and major blood vessels. In the CNS, Fmr2 expression begins at the time that cells in the neuroepithelium differentiate into neuroblasts. Mice lacking Fmr2 showed a delay-dependent conditioned fear impairment. Long-term potentiation (LTP) was found to be enhanced in hippocampal slices of Fmr2 knock-out compared with wild-type littermates. To our knowledge, this mouse knock-out is the first example of an animal model of human mental retardation with impaired learning and memory performance and increased LTP. Thus, although a number of studies have suggested that diminished LTP is associated with memory impairment, our data suggest that increased LTP may be a mechanism that leads to impaired cognitive processing as well.

Animals↗
PubMed2002

Missense mutations of the WASP gene cause intermittent X-linked thrombocytopenia.

Mutations of the WASP gene have been previously shown to be responsible for classical Wiskott-Aldrich syndrome, isolated X-linked thrombocytopenia, and severe, congenital X-linked neutropenia. We report herewith 2 families in which affected males had a history of intermittent thrombocytopenia with consistently reduced platelet volume, in the absence of other major clinical features, and carried missense mutations of the WASP gene that allowed substantial protein expression. This observation broadens the spectrum of clinical phenotypes associated with WASP gene defects, and it indicates the need for molecular analysis in males with reduced platelet volume, regardless of the platelet number.

Adult↗
PubMed2002

Physical and genetic characterization reveals a pseudogene, an evolutionary junction, and unstable loci in distal Xq28.

A large portion of human Xq28 has been completely characterized but the interval between G6PD and Xqter has remained poorly understood. Because of a lack of stable, high-density clone coverage in this region, we constructed a 1.6-Mb bacterial and P1 artificial chromosome (BAC and PAC, respectively) contig to expedite mapping, structural and evolutionary analysis, and sequencing. The contig helped to reposition previously mismapped genes and to characterize the XAP135 pseudogene near the int22h-2 repeat. BAC clones containing the distal int22h repeats also demonstrated spontaneous rearrangements and sparse coverage, which suggested that they were unstable. Because the int22h repeats are involved in genetic diseases, we examined them in great apes to see if they have always been unstable. Differences in copy number among the apes, due to duplications and deletions, indicated that they have been unstable throughout their evolution. Taking another approach toward understanding the genomic nature of distal Xq28, we examined the homologous mouse region and found an evolutionary junction near the distal int22h loci that separated the human distal Xq28 region into two segments on the mouse X chromosome. Finally, haplotype analysis showed that a segment within Xq28 has resisted excessive interchromosomal exchange through great ape evolution, potentially accounting for the linkage disequilibrium recently reported in this region. Collectively, these data highlight some interesting features of the genomic sequence in Xq28 and will be useful for positional cloning efforts, mouse mutagenesis studies, and further evolutionary analyses.

Animals↗
PubMed2002

The human secretin gene: fine structure in 11p15.5 and sequence variation in patients with autism.

Secretin is a peptide hormone involved in digestion that has been studied as a potential therapeutic agent in patients with autism. We characterized the human secretin locus to determine whether mutations in this gene might play a role in a fraction of autism patients. While the secretin gene (SCT) was not found to be mutated in the majority of autistic patients, rare heterozygous sequence variants were identified in three patients. We also investigated length variation in a variable number of tandem repeats (VNTR) immediately upstream of SCT and found no significant differences in length between patients with autism and normal controls. SCT is located on 11p15.5, adjacent to DRD4 and HRAS. This region has been reported to be associated with both autism and attention deficit hyperactivity disorder (ADHD). Although imprinting is a characteristic of some genes in the vicinity, we could find no evidence for methylation of SCT in lymphoblast cells from patients or control individuals.

Amino Acid Sequence↗
PubMed2002

Instability of a premutation-sized CGG repeat in FMR1 YAC transgenic mice.

Fragile X syndrome results from the massive expansion of a CGG repeat in the 5' untranslated region of the gene FMR1. Data suggest that the hyperexpansion properties of FMR1 CGG repeats may depend on flanking cis-acting elements. We have therefore used homologous recombination in yeast to introduce an in situ CGG expansion corresponding to a premutation-sized allele into a human YAC carrying the FMR1 locus. Several transgenic lines were generated that carried repeats of varying lengths and amounts of flanking sequence. Length-dependent instability in the form of small expansions and contractions was observed in both male and female transmissions over five generations. No parent-of-origin effect or somatic instability was observed. Alterations in tract length were found to occur exclusively in the 3' uninterrupted CGG tract. Large expansion events indicative of a transition from a premutation to a full mutation were not observed. Overall, our results indicate both similarities and differences between the behavior of a premutation-sized repeat in mouse and that in human.

Animals↗
PubMed2002

Atomoxetine increases extracellular levels of norepinephrine and dopamine in prefrontal cortex of rat: a potential mechanism for efficacy in attention deficit/hyperactivity disorder.

The selective norepinephrine (NE) transporter inhibitor atomoxetine (formerly called tomoxetine or LY139603) has been shown to alleviate symptoms in Attention Deficit/Hyperactivity Disorder (ADHD). We investigated the mechanism of action of atomoxetine in ADHD by evaluating the interaction of atomoxetine with monoamine transporters, the effects on extracellular levels of monoamines, and the expression of the neuronal activity marker Fos in brain regions. Atomoxetine inhibited binding of radioligands to clonal cell lines transfected with human NE, serotonin (5-HT) and dopamine (DA) transporters with dissociation constants (K(i)) values of 5, 77 and 1451 nM, respectively, demonstrating selectivity for NE transporters. In microdialysis studies, atomoxetine increased extracellular (EX) levels of NE in prefrontal cortex (PFC) 3-fold, but did not alter 5-HT(EX) levels. Atomoxetine also increased DA(EX) concentrations in PFC 3-fold, but did not alter DA(EX) in striatum or nucleus accumbens. In contrast, the psychostimulant methylphenidate, which is used in ADHD therapy, increased NE(EX) and DA(EX) equally in PFC, but also increased DA(EX) in the striatum and nucleus accumbens to the same level. The expression of the neuronal activity marker Fos was increased 3.7-fold in PFC by atomoxetine administration, but was not increased in the striatum or nucleus accumbens, consistent with the regional distribution of increased DA(EX). We hypothesize that the atomoxetine-induced increase of catecholamines in PFC, a region involved in attention and memory, mediates the therapeutic effects of atomoxetine in ADHD. In contrast to methylphenidate, atomoxetine did not increase DA in striatum or nucleus accumbens, suggesting it would not have motoric or drug abuse liabilities.

Animals↗
PubMed2002

R-fluoxetine increases extracellular DA, NE, as well as 5-HT in rat prefrontal cortex and hypothalamus: an in vivo microdialysis and receptor binding study.

The selective serotonin reuptake inhibitor fluoxetine consists of equal amounts of R and S stereoisomers. In this study, we investigated the pharmacologic properties of the stereoisomers using transporter and receptor binding assays and in vivo microdialysis in freely moving rats. Binding to the transporter confirmed selectivity of R- and S-fluoxetine for the 5-HT transporter versus the dopamine (DA) and norepinephrine (NE) human transporters. Receptor binding studies demonstrated significant affinity of R-fluoxetine, but not S-fluoxetine, for human 5-HT(2A) and 5-HT(2C) receptor subtypes. Functional GTPgammaS binding studies indicated that R-fluoxetine is an antagonist at 5-HT(2A) and 5-HT(2C) receptors. In microdialysis studies, acute R- and S-fluoxetine increased extracellular levels of 5-HT, DA, and NE in prefrontal cortex (PFC), but R-fluoxetine caused significantly greater increases of catecholamines. R-fluoxetine increased extracellular levels of 5-HT and NE in PFC, nucleus accumbens, and hypothalamus, whereas it increased dopamine in PFC and hypothalamus, but not in DA-rich nucleus accumbens and striatum, thus indicating a regionally selective effect. The unexpected increases of extracellular catecholamines by a selective 5-HT uptake inhibitor like R-fluoxetine may be due to its antagonism of 5-HT(2C) receptors.

Animals↗
PubMed2002

Successful determination of lower inflection point and maximal compliance in a population of patients with acute respiratory distress syndrome.

OBJECTIVE: To compare the ease and efficacy of two commonly used methods for choosing optimal positive end-expiratory pressure (PEEP) in patients with acute respiratory distress syndrome: a static pressure-volume curve to determine the lower inflection point (P(flex)) and the "best PEEP" (PEEP(best)) as determined by the maximal compliance curve. DESIGN: Prospective study. SETTING: Medical and respiratory intensive care units of university-associated tertiary care hospital. PATIENTS: Twenty-eight patients on mechanical ventilation with acute respiratory distress syndrome. INTERVENTIONS: A critical care attending physician or fellow and an experienced respiratory therapist attempted to obtain both static pressure-volume curves and maximal compliance curves on 28 patients with acute respiratory distress syndrome by using established methods that were practical to everyday use. The curves then were used to determine both P(flex) and PEEP(best), and the results were compared. MEASUREMENT AND MAIN RESULTS: Our results showed at least one value for optimal PEEP was obtained in 26 of 28 patients (93%). P(flex) was determined in 19 (68%), a PEEP(best) in 24 (86%), and both values in 17 (61%). In patients who had both P(flex) and PEEP(best) determined, there was a close concordance (+/-3 cm H2O) in 60%. When the values of P(flex) and PEEP(best) were interpreted by two additional investigators, there was unanimous agreement on the P(flex) (+/-3) only 64% of the time. There was agreement on the value of PEEP(best) 93% of the time. CONCLUSIONS: Our data show that optimal PEEP, as determined by a pressure-volume curve and a maximal compliance curve, are sometimes unobtainable by practical means but, when obtained, often correspond. A maximal compliance is more often identified, has less interobserver variability, and poses less risk to the patient. We conclude that determining optimal PEEP by maximal static compliance may be easier to measure and more frequently obtained at the bedside than by using a static pressure-volume curve.

Adult↗
PubMed2002

Complex SNP-based haplotypes in three human helicases: implications for cancer association studies.

We have initiated a candidate gene approach to study variation and predisposition to cancer in the four major ethnic groups that constitute the U.S. population (African Americans, Caucasians, Hispanics, and Asians). We resequenced portions of three helicase genes (BLM, WRN, and RECQL) identifying a total of 37 noncoding single nucleotide polymorphisms (SNPs). Haplotype inference predicted 50 haplotypes in BLM, 56 in WRN, and 47 in RECQL in a sample of 600 chromosomes. Approximately 10% of the predicted haplotypes were shared among all ethnic groups. Linkage disequilibrium and recombination effects showed that each locus has taken a diverse evolutionary path. Primate DNA analysis of the same loci revealed one human haplotype per gene shared with the great apes, indicating that the observed diversity occurred since the divergence of humans from the last common ancestor. In BLM, we confirmed the presence of a founder haplotype among Ashkenazi Jews homozygous for the blm(Ash) mutation. The cosegregating haplotype was seen in all (6/6) samples of Ashkenazi descent, whereas in the general population it has a low frequency (0.02) and was not found in African Americans. In WRN, ethnic samples were studied for their haplotype content and the presence or absence of six previously described coding SNPs (cSNPs). Hispanic individuals carrying two of these cSNPs showed a 60% increase in the frequency of a common haplotype (haplotype No. 28). In the pooled sample, no association was found. Because (1) the majority of the haplotypes are population specific and (2) the patterns of linkage disequilibrium, recombination, and haplotype diversity are markedly different between gene regions, these data show the importance of either ethnically matched controls or within-family-based disease-gene association studies.

Alleles↗
PubMed2002

Haplotype and linkage disequilibrium architecture for human cancer-associated genes.

To facilitate association-based linkage studies we have studied the linkage disequilibrium (LD) and haplotype architecture around five genes of interest for cancer risk: ATM, BRCA1, BRCA2, RAD51, and TP53. Single nucleotide polymorphisms (SNPs) were identified and used to construct haplotypes that span 93-200 kb per locus with an average SNP density of 12 kb. These markers were genotyped in four ethnically defined populations that contained 48 each of African Americans, Asian Americans, Hispanic Americans, and European Americans. Haplotypes were inferred using an expectation maximization (EM) algorithm, and the data were analyzed using D', R(2), Fisher's exact P-values, and the four-gamete test for recombination. LD levels varied widely between loci from continuously high LD across 200 kb to a virtual absence of LD across a similar length of genome. LD structure also varied at each gene and between populations studied. This variation indicates that the success of linkage-based studies will require a precise description of LD at each locus and in each population to be studied. One striking consistency between genes was that at each locus a modest number of haplotypes present in each population accounted for a high fraction of the total number of chromosomes. We conclude that each locus has its own genomic profile with regard to LD, and despite this there is the widespread trend of relatively low haplotype diversity. As a result, a low marker density should be adequate to identify haplotypes that represent the common variation at a locus, thereby decreasing costs and increasing efficacy of association studies.

Alleles↗
PubMedDate not supplied

Interrater reliability, concurrent validity, responsiveness, and predictive validity of the Melville-Nelson Self-Care Assessment.

OBJECTIVE: This study examines psychometric characteristics of the Melville-Nelson Self-Care Assessment (SCA), which is designed for occupational therapists working in skilled nursing facilities (SNFs) and subacute rehabilitation. Like the federally mandated Minimum Data Set, the SCA assesses seven self-care occupations in two ways: self-performance and support needed. METHOD: Participants were SNF patients receiving subacute rehabilitation. Primary and secondary diagnoses varied widely; mean age was 76.5 years (SD = 9.8). Using the SCA, the Functional Independence Measure (FIM), and the Klein-Bell Activities of Daily Living Scale, four teams of raters independently and simultaneously assessed 54 women and 14 men at admission and discharge; 40 participants were available for reassessment in their homes after discharge. RESULTS: Total self-performance scores on the SCA showed (a) interrater reliability (mean ICC = .94); (b) concurrent validity with relevant areas of the FIM (rho = -.85) and the Klein-Bell (rho = -.86); (c) responsiveness in detecting change from admission to discharge, t(67) = 6.3, p < .001, with a large effect size of 1.10; and (d) moderate predictive validity of caregiving time in the home (rho = -.44) and overall function in the home as measured by the total FIM (rho = -.55) and total Klein-Bell (rho = -.54) scores. The self-performance and support measures for the seven self-care areas all had acceptable interrater reliability and concurrent validity. Eating, personal hygiene, and bathing showed little or no responsiveness to change from admission to discharge, whereas positive change was substantial in bed mobility, transfers, dressing, and toileting. CONCLUSION: This instrument is recommended for use as part of a comprehensive occupational therapy model of practice in SNFs and subacute rehabilitation.

Activities of Daily Living↗
PubMedDate not supplied

Patients' perspectives on the self-identified goals assessment.

OBJECTIVE: The purpose of this study was to investigate patients' perspectives of the validity of the Self-Identified Goals Assessment (SIGA), which is designed for use by occupational therapists working in subacute rehabilitation and skilled nursing facilities. The SIGA has two primary purposes: (a) to help the patient identify personally meaningful occupational goals to be addressed in therapy and (b) to evaluate changing levels of patient-defined success in desired occupations. METHOD: Participants (20 women, 10 men) were patients with varied diagnosed conditions at a hospital-based subacute facility. Their mean age was 73.4 years (SD = 12.2). The SIGA was administered by the patients' regular occupational therapy practitioner after admission and before discharge; a graduate student followed up each administration of the SIGA by asking participants fixed-alternative and open-ended questions about the usefulness of the assessment. Fixed-alternative questions were analyzed as simple dichotomies, and open-ended questions were analyzed through categorization into convergent and divergent themes across participants. RESULTS: Twenty-nine of the 30 participants confirmed the personal meaningfulness of goals identified in the SIGA admissions interview, and 28 reported that they thought the SIGA helped the therapist realize what was personally important to them. On admission, 9 participants reported difficulty quantifying their performance on the 0-to-10 scale; however, 27 reported that their scores were accurate self-assessments. Participants' perspectives of the SIGA tended to be particularly positive at discharge. CONCLUSION: Given the lack of efficient, structured approaches to the measurement of self-identified goals in subacute and skilled nursing facilities, the SIGA tentatively is recommended for use in these settings, pending future research.

Aged↗
PubMedDate not supplied

Effect of an occupational intervention on printing in children with economic disadvantages.

OBJECTIVE: The purpose of this study was to evaluate whether an occupational therapy intervention improved an academic outcome (D'Nealian printing) in a school setting. The study specifically examined improvement in printing skills in economically disadvantaged first graders who were at risk academically and socially. The intervention was based on an occupational framework including biomechanical, sensorimotor, and teaching-learning strategies. METHOD: The final sample consisted of 59 first-grade children from a low socioeconomic urban elementary school-based health center who were randomly assigned to an occupational therapy intervention or a control condition. In addition to regular academic instruction, the intervention group received 10 weeks of training twice a week for 30-minute sessions. The control group received only regular academic instruction. Subjects were pretested and posttested on the Minnesota Handwriting Test, which assesses legibility, space, line, size, and form (the main variables in this study) as well as speed. RESULTS: Multivariate analysis of variance confirmed that the gain scores in the occupational therapy intervention group were significantly greater than those in the control group. The Hotelling-Lawley Trace value was 0.606, with F(5, 53) = 6.43, p < .0001). The estimated effect size (eta2) was .378, with an observed power of .994. Largest gains for the intervention group were in the areas of space, line, and size. CONCLUSION: The intervention group demonstrated a significant increase in scores on the posttest of the Minnesota Handwriting Test when compared to the scores of the control group. Occupational intervention was effective in improving the academic outcome of printing in children who are economically disadvantaged.

Child↗