Biomedical subjects

D Discher

Publications and source records attributed to D Discher.

5 recordsLinked to original sources

PubMed1997

Case-control study of malignant melanoma among employees of the Lawrence Livermore National Laboratory.

During 1972 to 1977, the Lawrence Livermore National Laboratory (LLNL) experienced increased diagnosis of malignant melanoma among employees. In 1984, a report on the results of a case-control study of 39 cases concluded that occupational factors, including exposures to ionizing radiation and to chemicals, caused the excess incidence. The study reported here, based on results from 69 case-control pairs, re-examines the role of the occupational factors implicated by the earlier study in melanoma causation. Results from this study suggest that constitutional factors, including skin reactivity to sunlight, sunbathing frequency, and number of moles, explain most of the excess melanoma. Exposures to occupational factors, including ionizing radiation and chemicals, were found to be no different in cases than in controls.

Algorithms↗

PubMed1996

Detection of altered membrane phospholipid asymmetry in subpopulations of human red blood cells using fluorescently labeled annexin V.

The phospholipids of the human red cell are distributed asymmetrically in the bilayer of the red cell membrane. In certain pathologic states, such as sickle cell anemia, phospholipid asymmetry is altered. Although several methods can be used to measure phospholipid organization, small organizational changes have been very difficult to assess. Moreover, these methods fail to identify subpopulations of cells that have lost their normal phospholipid asymmetry. Using fluorescently labeled annexin V in flow cytometry and fluorescent microscopy, we were able to identify and quantify red cells that had lost their phospholipid asymmetry in populations as small as 1 million cells. Moreover, loss of phospholipid organization in subpopulations as small as 0.1% of the total population could be identified, and individual cells could be studied by fluorescent microscopy. An excellent correlation was found between fluorescence-activated cell sorter (FACS) analysis results using annexin V to detect red cells with phosphatidylserine (PS) on their surface and a PS-requiring prothrombinase assay using similar red cells. Cells that bound fluorescein isothiocyanate (FITC)-labeled annexin V could be isolated from the population using magnetic beads covered with an anti-FITC antibody. Evaluation of blood samples from patients with sickle cell anemia under oxygenated conditions demonstrated the presence of subpopulations of cells that had lost phospholipid asymmetry. While only a few red cells were labeled in normal control samples (0.21% +/- 0.12%, n = 8), significantly increased (P < .001) annexin V labeling was observed in samples from patients with sickle cell anemia (2.18% +/- 1.21%, n = 13). We conclude that loss of phospholipid asymmetry may occur in small subpopulations of red cells and that fluorescently labeled annexin V can be used to quantify and isolate these cells.

Anemia, Sickle Cell↗

PubMed1995

Evolutionarily conserved alternative pre-mRNA splicing regulates structure and function of the spectrin-actin binding domain of erythroid protein 4.1.

A developmental alternative splicing switch, involving exon 16 of protein 4.1 pre-mRNA, occurs during mammalian erythropoiesis. By controlling expression of a 21-amino acid peptide required for high-affinity interaction of protein 4.1 with spectrin and actin, this switch helps to regulate erythrocyte membrane mechanical stability. Here we show that key aspects of protein 4.1 structure and function are conserved in nucleated erythroid cells of the amphibian Xenopus laevis. Analysis of protein 4.1 cDNA sequences cloned from Xenopus erythrocytes and oocytes showed that tissue-specific alternative splicing of exon 16 also occurs in frogs. Importantly, functional studies with recombinant Xenopus erythroid 4.1 demonstrated specific binding to and mechanical stabilization of 4.1-deficient human erythrocyte membranes. Phylogenetic sequence comparison showed two evolutionarily conserved peptides that represent candidate spectrin-actin binding sites. Finally, in situ hybridization of early embryos showed high expression of 4.1 mRNA in ventral blood islands and in developing brain structures. These results demonstrate that regulated expression of structurally and functionally distinct protein 4.1 isoforms, mediated by tissue-specific alternative splicing, has been highly evolutionarily conserved. Moreover, both nucleated amphibian erythrocytes and their enucleated mammalian counterparts express 4.1 isoforms functionally competent for spectrin-actin binding.

Actins↗

PubMed1993

Mechanochemistry of the alternatively spliced spectrin-actin binding domain in membrane skeletal protein 4.1.

Protein 4.1's interaction with the erythroid skeletal proteins spectrin and actin and its essential role in regulating membrane strength are both attributable to expression of an alternatively spliced 63-nucleotide exon. The corresponding 21-amino acid (21-aa) cassette is within the previously identified spectrin-actin binding domain (10 kDa molecular mass) of erythroid protein 4.1. This cassette is absent, however, in several isoforms that are generated by tissue- and development-specific RNA splicing. Four isoforms of the 10-kDa domain were constructed for comparative assessment of functions particularly relevant to red cells. In vitro translated isoforms containing the 21-aa cassette, denoted 10k21 and 10k19,21, were able to bind spectrin, stabilize spectrin-actin complexes, and associate with red cell membrane. Isoforms replacing or lacking the 21-aa cassette, 10k19 and 10k0, did not function in these assays. A bacterially expressed fusion protein with glutathione-S-transferase, designated GST-10k21, congealed spectrin-actin into a network in vitro as found with purified protein 4.1. Additionally, incorporation of GST-10k21 into mechanically weak, 4.1-deficient membranes increased mechanical strength of these membranes to normal. GST-10k19 did not function in these assays. These results show that the 21-aa sequence in protein 4.1 is critical to mechanical integrity of the red cell membrane. These results also allow the role of protein 4.1 in membrane mechanics to be interpreted primarily in terms of its spectrin-actin binding function. Alternatively expressed sequences within the 10-kDa domain of nonerythroid protein 4.1 are suggested to have different, yet to be defined functions.

Actins↗

PubMedDate not supplied

Occupational respiratory function testing--an algorithmic approach.

Pulmonary function testing is an essential component of many occupational respiratory programs. Testing is performed for several different reasons. Proper selection of tests depends on whether they are used for screening a healthy population, establishment of a clinical diagnosis in a specific individual, or determination of work ability or disability. There are many pulmonary conditions and relevant exposures. The appropriate tests should be chosen based on the specific situation.

Algorithms↗