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W J Nelson

Publications and source records attributed to W J Nelson.

At least 127 records · Page 7Linked to original sources
PubMed1988

Workers' compensation: 1980-84 benchmark revisions.

The first workers' compensation program was introduced 80 years ago. Its purpose was to compensate occupationally injured workers and their families for lost wages and medical expenses from job-related injury, regardless of fault. Today, each of the State and Federal programs that provides coverage to more than 86 percent of the work force uses a combination of private insurance, State or Federal funds, and self-insurance to meet its benefit obligations. The workers' compensation program is of continuing interest to the Social Security Administration (SSA) for several reasons. Since 1965, Social Security Disability Insurance benefits have been subject to reduction if such benefits, when combined with those provided under workers' compensation laws, exceed 80 percent of the worker's earnings. Because the two programs have gaps in protection as well as duplication in coverage, a periodic review of the workers' compensation program is necessary. In addition, SSA administers Part B of the Black Lung program--established to provide income-maintenance protection to coal miners disabled by pneumoconiosis--to about 1 million beneficiaries whose claims were filed before July 1973. This article provides revised benchmark data on the workers' compensation programs and presents a review of program operations during the early 1980's.

Costs and Cost Analysis↗
PubMed1987

Modulation of fodrin (membrane skeleton) stability by cell-cell contact in Madin-Darby canine kidney epithelial cells.

During growth of Madin-Darby canine kidney (MDCK) epithelial cells, there is a dramatic change in the stability, biophysical properties, and distribution of the membrane skeleton (fodrin) which coincides temporally and spatially with the development of the polarized distribution of the Na+, K+-ATPase, a marker protein of the basolateral domain of the plasma membrane. These changes occur maximally upon the formation of a continuous monolayer of cells, indicating that extensive cell-cell contact may play an important role in the organization of polarized MDCK cells (Nelson, W. J., and P. J. Veshnock, 1986, J. Cell Biol., 103:1751-1766). To directly analyze the role of cell-cell contact in these events, we have used an assay in which the organization of fodrin and membrane proteins is analyzed in confluent monolayers of MDCK cells in the absence or presence of cell-cell contact by adjusting the concentration Ca++ in the growth medium. Our results on the stability and solubility properties of fodrin reported here show directly that there is a positive correlation between cell-cell contact and increased stability and insolubility of fodrin. Furthermore, we show that fodrin can be recruited from an unstable pool of protein to a stable pool during induction of cell-cell contact; significantly, the stabilization of fodrin is not affected by the addition of cyclohexamide, indicating that proteins normally synthesized during the induction of cell-cell contact are not required. Together these results indicate that cell-cell contact may play an important role in the development of polarity in MDCK cells by initiating the formation of a stable, insoluble matrix of fodrin with preexisting (membrane) proteins at the cell periphery. This matrix may function subsequently to trap proteins targeted to the membrane, resulting in the maintenance of membrane domains.

Animals↗
PubMed1987

Nonmitogenic morphoregulatory action of pp60v-src on multicellular epithelial structures.

Madin-Darby canine kidney (MDCK) cells form polarized, multicellular epithelial structures in vitro. Low-level expression of pp60v-src in MDCK cells elicits plasticity in these multicellular structures. Plasticity was revealed by the displacement of cells from mechanically stressed regions of the epithelial monolayers; however, the two-dimensional relationship between the cells in the remainder of the monolayer was maintained. Electron microscopy of multicellular structures revealed abnormal separation of the lateral membranes of adjacent cells and selective uncoupling of the junctional complex; the zonula adherens was disrupted, but the zonula occludens and desmosomes were retained. Significantly, this result was not accompanied by transformation of the cells, as judged by the absence of anchorage-independent growth potential. These results demonstrate a nonmitogenic biological activity of pp60v-src which is experimentally dissociable from transformation. This morphoregulatory action on higher-order epithelial structures may reflect a function of related cellular tyrosine kinases.

Animals↗
PubMed1986

Dynamics of membrane-skeleton (fodrin) organization during development of polarity in Madin-Darby canine kidney epithelial cells.

Madin-Darby canine kidney (MDCK) epithelial cells exhibit a polarized distribution of membrane proteins between the apical and basolateral domains of the plasma membrane. We have initiated studies to investigate whether the spectrin-based membrane skeleton plays a role in the establishment and maintenance of these membrane domains. MDCK cells express an isoform of spectrin composed of two subunits, Mr 240,000 (alpha-subunit) and Mr 235,000 (gamma-subunit). This isoform is immunologically and structurally related to fodrin in lens and brain cells, which is a functional and structural analog of alpha beta-spectrin, the major component of the erythrocyte membrane skeleton. Analysis of fodrin in MDCK cells by immunoblotting, immunofluorescence, and metabolic labeling revealed significant changes in the biophysical properties, subcellular distribution, steady-state levels, and turnover of the protein during development of a continuous monolayer of cells. The changes in the cellular organization of fodrin did not appear to coincide with the distributions of microfilaments, microtubules, or intermediate filaments. These changes result in the formation of a highly insoluble, relatively dense and stable layer of fodrin which appears to be localized to the cell periphery and predominantly in the region of the basolateral plasma membrane of MDCK cells in continuous monolayers. The formation of this structure coincides temporally and spatially with extensive cell-cell contact, and with the development of the polarized distribution of the Na+, K+-ATPase, a marker protein of the basolateral plasma membrane.

Animals↗
PubMed1985

Expression and assembly of the erythroid membrane-skeletal proteins ankyrin (goblin) and spectrin in the morphogenesis of chicken neurons.

The membrane-skeleton of adult chicken neurons in the cerebellum and optic system is composed of polypeptides structurally and functionally related to the erythroid proteins spectrin and ankyrin, respectively. Neuronal spectrin comprises two distinct complexes that share a common alpha subunit (Mr 240,000) but which have structurally distinct polymorphic subunits (beta' beta spectrin; Mr 220/225,000; gamma spectrin, Mr 235,000); the brain-specific form (alpha gamma spectrin or fodrin) and an erythrocyte-specific form (alpha beta' beta spectrin). Two structurally related isoforms of ankyrin have also been identified and are termed alpha (Mr 260,000) and beta (Mr 237,000) ankyrin. Immunofluorescence demonstrates that the variants of spectrin and ankyrin, respectively, have different distributions within neurons. On the one hand, alpha gamma spectrin and beta ankyrin are present throughout the neuron, in the perikaryon, dendrites, and axon, whereas alpha beta' spectrin and alpha ankyrin are localized exclusively in the perikaryon and dendrites where they are actively segregated from alpha gamma spectrin and other components of axonal transport. This asymmetric distribution of spectrin and ankyrin isoforms is established in distinct stages during neuronal morphogenesis. Early in cerebellar and retinal development, alpha gamma spectrin is expressed in mitotic cells. Subsequently beta ankyrin and alpha gamma spectrin are coexpressed in postmitotic cells and gradually accumulate on the plasma membrane in a uniform pattern throughout the neuron during the phase of cell growth. At the onset of synaptogenesis and the cessation of cell growth, their levels of synthesis decline sharply while the assembled proteins remained as stable membrane components. Concomitantly, there is a dramatic induction in the accumulation of alpha ankyrin and alpha beta' spectrin, whose assembly is limited to the plasma membrane of the perikarya and dendrites. These results demonstrate that two successive, developmentally regulated programs of ankyrin and spectrin expression and patterning on the plasma membrane are involved in the assembly of the spectrin-based asymmetry in the neuronal membrane-skeleton, and that their asymmetric distribution is actively maintained throughout the life of the neuron.

Animals↗
PubMed1985

Interaction in vitro of the neurofilament triplet proteins from porcine spinal cord with natural RNA and DNA.

Neurofilaments were isolated from porcine spinal cord and separated into their subunit proteins (68 Kd NFP, 145 Kd NFP, 200 Kd NFP) by ion exchange chromatography on DEAE-cellulose in 6 M urea. The individual proteins were reacted with total rRNA from Ehrlich ascites tumor cells and the reaction products analysed by sucrose gradient centrifugation at low ionic strength and in the presence of EDTA. All three proteins interacted with rRNA with a preference for 18S rRNA. Competition experiments with native and heat-denatured calf thymus DNA showed that the affinities of the 68 Kd and 145 Kd NFPs were considerably higher for denatured DNA than for rRNA and that native DNA was only a weak competitor. The binding of the 200 Kd NFP to rRNA was unaffected by native and by denatured DNA. When denatured DNA was reacted with a mixture of the 68 Kd and 145 Kd NFPs, the two proteins interacted independently with the nucleic acid, giving rise to two different populations of deoxyribonucleoprotein particles. This segregation is the result of the cooperative interaction of the neurofilament proteins with single-stranded DNA. It could not be observed with rRNA or bacteriophage MS2 RNA. The results clearly show that the 68 Kd and 145 Kd NFPs are single-stranded RNA- and DNA-binding proteins, whereas the 200 Kd NFP seems to be only a single-stranded RNA-binding protein.

Animals↗
PubMed1985

Posttranslational control of membrane-skeleton (ankyrin and alpha beta-spectrin) assembly in early myogenesis.

Adult chicken skeletal muscle cells express polypeptides that are antigenically related to alpha-spectrin (Mr 240,000) and beta-spectrin (Mr 220,000-225,000), the major components of the erythrocyte membrane-skeleton, and to ankyrin (Mr 237,000; also termed goblin in chicken erythrocytes), which binds spectrin to the transmembrane anion transporter in erythrocytes. Comparative immunoblotting of SDS-solubilized extracts of presumptive myoblasts and fully differentiated myotubes cultured in vitro demonstrated that there is a dramatic accumulation of ankyrin and alpha- and beta-spectrin during myogenesis and a concomitant switch in the subunit composition of spectrin from alpha gamma to alpha beta. Analysis of early time points in myogenesis (12-96 h) revealed that these changes occur shortly after the main burst of cell fusion. To determine the temporal relationship between cell fusion and the accumulation of ankyrin and alpha- and beta-spectrin, we treated presumptive myoblasts with 2 mM EGTA, which resulted in the complete inhibition of cell fusion. The incorporation of [35S]methionine into total protein and, specifically, into alpha-, gamma-, and beta-spectrin remained the same in EGTA-treated and control cells. Analysis by immunoblotting of the amounts of ankyrin and alpha- and beta-spectrin in fusion-blocked cells revealed that there was no effect on accumulation for the first 19 h. However, there was then a dramatic cessation in their accumulation, and thereafter, the amount of each protein at steady state remained constant. Upon release from the EGTA block, the cells fused rapidly (less than 11 h), and the accumulation of ankyrin and alpha- and beta-spectrin was reinitiated after a lag period of 3-5 h at a rate similar to that in control cells. The inhibition in the accumulation of newly synthesized ankyrin, alpha-spectrin, and beta-spectrin in EGTA-treated myoblasts was not characteristic of all structural proteins, since the accumulation of the muscle-specific intermediate filament protein desmin was the same in control and fusion-blocked cells. These results show that in myogenesis, the synthesis of ankyrin and alpha- and beta-spectrin and their accumulation as a complex, although concurrent, are not coupled events. We hypothesize that the extent of assembly of these components of the membrane-skeleton in muscle cells is determined by a control mechanism(s) operative at the posttranslational level that is triggered near the time of cell fusion and the onset of terminal differentiation.

Animals↗
PubMed1985

Fifty years ago.

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History, 20th Century↗
PubMed1984

The patterns of expression of two ankyrin isoforms demonstrate distinct steps in the assembly of the membrane skeleton in neuronal morphogenesis.

We have identified in chicken neurons two membrane-bound isoforms of goblin (ankyrin), the specific membrane attachment protein for spectrin in avian erythrocytes, which exhibit distinct patterns of expression and assembly during neuronal morphogenesis. Early in cerebellar and retinal development, neither goblin isoform is detected in mitotic cells. Subsequently, beta-goblin (Mr 237,000) is expressed in postmitotic cells, and gradually accumulates with alpha gamma (brain) spectrin on the neuronal plasma membrane during the phase of cell growth. At the onset of synaptogenesis and the cessation of cell growth, their levels of synthesis decline sharply while the assembled proteins remain as stable membrane components. Concomitantly, there is a dramatic induction in the accumulation of alpha-goblin (erythroid goblin; Mr 260,000) and alpha beta (erythroid) spectrin, whose assembly is limited to the plasma membrane of perikarya and dendrites.

Aging↗
PubMed1984

Segregation of two spectrin forms in the chicken optic system: a mechanism for establishing restricted membrane-cytoskeletal domains in neurons.

The chicken optic system contains a brain-specific form of spectrin (alpha gamma-spectrin or fodrin) as a major membrane-associated, axonally transported cytoskeletal protein. We show here that the chicken optic system also contains an erythrocyte-specific form of spectrin (alpha beta' beta-spectrin), which has a more restricted distribution; it is confined to the plasma membrane of dendrites and cell bodies of retinal ganglion cells, is absent from the optic nerve fibers, and is not axonally transported from the retina into the optic nerve. During development of the optic system, the expression of alpha gamma-spectrin is constitutive in all cell types. On the other hand, the accumulation of alpha beta' beta-spectrin is detected in only the ganglion cells, and at a time in development which coincides with the phase of synaptogenesis. These results indicate the existence of a developmentally regulated mechanism that topologically segregates the erythroid and brain forms of spectrin from each other, and the former from axonal transport, and suggest that erythroid spectrin may be involved in establishing restricted membrane-cytoskeletal domains in neurons during synaptogenesis, and maintaining them in the adult cell.

Animals↗
PubMed1984

Goblin (ankyrin) in striated muscle: identification of the potential membrane receptor for erythroid spectrin in muscle cells.

Goblin , a high molecular weight (Mr, 260,000) polypeptide of avian erythrocyte plasma membranes characterized by hormone-dependent phosphorylation, is shown by a variety of criteria to be the avian equivalent of ankyrin, the membrane attachment protein for spectrin; a polyclonal monospecific goblin antiserum reacts specifically with ankyrin from mammalian erythrocyte ghosts; goblin and ankyrin have highly homologous, although distinct, two-dimensional peptide maps; and, in reconstitution experiments, goblin binds to spectrin and band 3 in approximately the same molar ratio as ankyrin. Immunoautoradiography and immunofluorescence with goblin antiserum reveal that a serologically related polypeptide (Mr, 235,000) is present in highly purified membrane fractions of mammalian myocardium and in whole extracts of adult chicken cardiac and skeletal muscle-nonerythroid tissues which express predominantly the erythroid (alpha beta-) spectrin phenotype. Erythroid spectrin and goblin (ankyrin) are codistributed in skeletal muscle at the sarcolemma as discrete foci adjacent to the Z lines and, in pectoral muscle, also at the periphery of the Z discs. These spatial relationships indicate that goblin and spectrin in muscle cells form a structural framework that serves as the attachment site for the myofiber at the level of the Z line on the sarcolemma.

Animals↗
PubMed1984

Changing the method for calculating quarters of coverage: the impact on workers' insured status.

The 1977 Social Security Amendments specified that, beginning in 1978, a worker would be credited with one quarter of coverage for a designated amount of annual earnings. For 1978, a worker received one quarter of coverage (up to a total of four) for each $250 in annual earnings from employment or self-employment. Before 1978, a worker who was paid $50 in wages in a calendar quarter was credited with a quarter of coverage. A person who had $400 or more in self-employment income in a year was credited with four quarters of coverage. Some workers received more quarters of coverage under the new provisions than they would have under the old, and other workers received less. Since a worker's receipt of benefits depends on his or her insured status, which is based on quarters of coverage, this change can affect a worker's eligibility for benefits. This study indicates that if $250 in annual earnings had been required for one quarter of coverage in 1977, more than 2.1 million workers would have had a change in their insured status for disabled worker benefits, and about 700,000 workers would have had a change in their insured status for survivor benefits. Those whose insured status was affected were most likely to have had marginal earnings records--for example, they had four to seven quarters of coverage when six were needed. (This effect was expected when the legislation was passed.) This article examines those whose eligibility for benefits was most likely to have been affected.

Adolescent↗
PubMed1983

Erythrocyte form of spectrin in cerebellum: appearance at a specific stage in the terminal differentiation of neurons.

The developing chicken cerebellum contains two forms of the plasma membrane-associated actin-binding protein spectrin. The brain form, alpha gamma-spectrin (fodrin), is expressed constitutively in all neuronal cell bodies and processes during all stages of cerebellar morphogenesis. On the other hand, the erythrocyte form, alpha beta'beta-spectrin, accumulates exclusively at the plasma membrane of the cell bodies of Purkinje and granule cells and of neurons in cerebellar nuclei, but only after these cells have become postmitotic and have completed their migration to their final positions in the cerebellum. The appearance of alpha beta'beta-spectrin coincides temporally with the establishment of axosomatic contacts on these three neuronal cell types, which suggests that alpha beta'beta-spectrin accumulates in response to the formation of functional synaptic connections during cerebellar ontogeny.

Animals↗
PubMed1983

Erythrocyte and brain forms of spectrin in cerebellum: distinct membrane-cytoskeletal domains in neurons.

Chicken cerebellum expresses a polypeptide antigenically and biochemically related to the alpha subunit of spectrin, an erythrocyte membrane-cytoskeletal protein. Most of this polypeptide is associated with a brain specific spectrin subunit, gamma-spectrin, and is localized in virtually all neuronal cell bodies and processes. Cerebellum also expresses polypeptides antigenically related to the beta subunits of erythrocyte spectrin and these are also found in association with cerebellar alpha-spectrin but are confined to the plasmalemma of the neuronal cell bodies. This suggests that there is a mechanism for segregating different spectrin complexes into distinct membrane domains within a single cell.

Animals↗
PubMed1983

The turnover of vimentin in Ehrlich ascites tumour cells.

The turnover of vimentin and vimentin-derived peptides has been examined in logarithmically growing Ehrlich ascites tumour cells. Cells were pulse-labelled with [35S]methionine for 30 min and then chased for up to 60 h. It was found that the specific radioactivity of the main isoelectric variant of vimentin decreased to half the original value in 15.3 h which was close to the division time of the cells (16 h). The protein moiety of the phosphorylated variant of vimentin also turned over very slowly, in contrast to the turnover rate of the phosphate group itself which has a half-life of 1.4 h. The role of the intermediate filament-specific, Ca2+-activated proteinase has been considered in relationship to the slow turnover of vimentin.

Animals↗