Task experience and children's working memory performance: a perspective from recall timing.

Working memory is an important theoretical construct among children, and measures of its capacity predict a range of cognitive skills and abilities. Data from 9- and 11-year-old children illustrate how a chronometric analysis of recall can complement and elaborate recall accuracy in advancing our understanding of working memory. A reading span task was completed by 130 children, 75 of whom were tested on 2 occasions, with sequence length either increasing or decreasing during test administration.

Pressure ulcers: implementation of evidence-based nursing practice.

Aims: A 2-year project was carried out to evaluate the use of multi-component, computer-assisted strategies for implementing clinical practice guidelines. This paper describes the implementation of the project and lessons learned. The evaluation and outcomes of implementing clinical practice guidelines to prevent and treat pressure ulcers will be reported in a separate paper.

The effect of two actin depolymerizing factors (ADF/cofilins) on actin filament turnover: pH sensitivity of F-actin binding by human ADF, but not of Acanthamoeba actophorin.

Actin depolymerizing factor (ADF) from vertebrates and actophorin from Acanthamoeba castellanii are members of a protein family that bind monomeric and polymeric actin and have been shown by microscopy to sever filaments. Here, we compare the properties of recombinant human ADF and actophorin using rabbit muscle actin. ADF binds tenfold more strongly than actophorin to monomeric actin (G-actin)-ATP, and both bind co-operatively to F-actin.

Fine-structural investigation of rat brain microvascular endothelial cells: tight junctions and vesicular structures in freshly isolated and cultured preparations.

A comparison was made between endothelial cells in freshly-isolated rat brain microvessels, and following culture of the cells for 1-10 days during growth to confluence. Attention focused on tight junctions and vesicular structures, as seen in thin sections and freeze-fracture replicas. Freshly-isolated vessels had an abnormal appearance, with a profusion of luminal microvillar processes, and extensive cytoplasmic vacuolation.

Nuclear envelope dynamics and nucleocytoplasmic transport.

We have combined structural, biochemical and recombinant DNA methods to explore molecular interactions involved in nuclear envelope assembly dynamics and nucleocytoplasmic transport. Electron microscopy has established the overall architecture of the envelope and the relationship between nuclear pores, lamina fibres and pore-connecting fibrils. The lamin proteins that constitute the lamina resemble intermediate filament proteins, and assemble and disassemble during mitosis in response to phosphorylation.

Selective digestion of nuclear envelopes from Xenopus oocyte germinal vesicles: possible structural role for the nuclear lamina.

We have used enzymic digestion as a structural probe to investigate components of the nuclear envelope of germinal vesicles from Xenopus oocytes. Previous studies have shown that these envelopes are composed of a double membrane in which nuclear pore complexes are embedded. The nuclear pore complexes are linked to a fibrous lamina that underlies the nucleoplasmic face of the envelope.

Association of gold-labelled nucleoplasmin with the centres of ring components of Xenopus oocyte nuclear pore complexes.

We have used heavy-metal shadowing to study the interaction of morphological components of Xenopus oocyte nuclear pore complexes with nucleoplasmin conjugated to colloidal gold. When microinjected into Xenopus oocytes, gold-labelled nucleoplasmin accumulated on the axis of the pores. Envelopes partially disrupted by treatment with low ionic strength buffer produced isolated islands of pores together with substantial quantities of rings deriving from the cytoplasmic and nucleoplasmic faces of the pores.

Preparation of shadowed nuclear envelopes from Xenopus oocyte germinal vesicles for electron microscopy.

Methods for examining the structure of the nuclear envelope of oocytes of Xenopus laevis by electron microscopy using metal shadowing have been developed and evaluated. Minor modifications were made to existing methods for preparing specimens by freeze drying, mainly to eliminate unnecessary steps and a rapid method for examining the structure and arrangement of nuclear envelope components, based on dehydration in an ethanol series followed by amyl acetate and then air drying, was also developed. The preservation of the lamina and connections between the nuclear pore complexes using the rapid air drying method was satisfactory for observing the fibrous components of the envelope and their attachment to the pores.

Chromatin-like artifacts from nuclear sap.

Nuclear sap, on fixation in glutaraldehyde, forms a fibrous network that resembles chromatin in its dimensions and staining properties. This artifactual network is easily confused with true chromatin fibres in sections of nuclei. With formaldehyde a homogeneous array of beads is produced.

The fixation of nuclei in glutaraldehyde.

The production of an artifactual network in the nuclear sap of the salivary glands of Drosophila has been investigated. Mechanical stress to the cells, 3% glutaraldehyde containing more than 4 mM calcium, tannins, or cacodylate buffer or whose temperature is above 10 degrees C all enhance this artifactual effect. Over the range pH 6.

Intranuclear electrophoresis of the chromatin of living cells.

Intranuclear electrophoresis of living cells under appropriate conditions causes the chromatin and nucleoli to move rapidly into the anodal side of the nucleus. In pig kidney cells, chromatin lengths attached to the nuclear envelope are oriented by the current and freed from surrounding non-oriented chromatin. Individual chromatin strands isolated in this way are often long and have not been subjected to the trauma of isolation from the nucleus.

The fine structure of human chromosomes isolated by shearing-sieving.

Chromosomes isolated by the new technique of shearing-sieving, even if unstained, show a less degraded organisation than those prepared for the electron microscope by other techniques. The chromosomes are banded, may show more bands if stretched, and the centromere is a precisely defined structure. Appearances resulting from this technique are compared with those from other techniques.

The fixation of nuclei and chromosomes.

Chromosomes in the nuclei of living salivary glands of Simulium have been observed with Nomarski optics and polarized light before and during irrigation with various fixatives. All cause loss of chromosomal organization to some degree. The best fixative is redistilled glutaraldehyde; even so, although it leaves the nucleus visually unaltered, a network forms in the nuclear sap and birefringence is lost.

Interpretation of the three-dimensional structure of living nuclei by specimen tilt.

A mechanism is described that enables a specimen to be tilted through a known angle and continuously observed under the highest power of the optical microscope. Objects can thus be localized accurately in space. This facility in conjunction with serial optical sectioning by Nomarski optics has been used to construct models of the arrangement of polytene chromosomes in nuclei of Drosophila, Simulium and Chironomus.