摘要:

Mammalian nuclei are complex organelles containing many functionally distinct nucleoprotein and protein particles in the size range 20–30 nm. This complexity hinders the study of structure‐function relationships within the mammalian nucleus. Element‐specific mapping using the energy‐filtered transmission electron microscope can provide novel information on protein and nucleic acid density within structures, facilitating the identification of biochemical heterogeneity within morphologically similar structures. We demonstrate that imaging phosphorus, nitrogen and carbon can be useful in the characterization of protein and nucleoprotein structures within the nucleus. Additionally, electron spectroscopic imaging (ESI) may be used to map the distribution of stains relative to unstained material when biochemical‐specific staining protocols, such as EDTA‐regressive staining of RNA with uranyl acetate, are used. Relative mass may also be determined from ESI images and can be combined with elemental information further to distinguish biological constituents. Using this approach, heterochromatin was found to be variable in nucleic acid content although the morphology appeared relatively homogeneous. ESI shows substantial promise for the investigation of structure–function relationships in biolo

ISSN:0022-2720    

DOI:10.1046/j.1365-2818.1996.123403.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

SummaryLipid‐water mixtures were studied by X‐ray cryodiffraction in order to assess the structural changes during freezing. We show that the water of aqueous lipid phases, in the concentration range of 10–30% (water weight/total weight), is vitrified by high‐pressure freezing. Vitrified lipid phases can be cryo‐sectioned and imaged by electron cryomicroscopy. Both the ideal or average and the real or local structures of the lipid mixtures can be studied at a resolution better than 2 nm. While the average structure of the lipid phases is in good agreement with that determined by X‐ray diffraction, the local structure reveals features that might play an important role in the function of biological membranes such as in endo‐ a

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1996.tb04793.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

SummaryPseudowollastonite ceramic (psW) composed of CaO·SiO2was found to be bioactive in a simulated body fluid environment. The chemical reaction initiated at the material surface resulted in hydroxyapatite (HA)formation. These bone‐bonding properties are essential for securing the necessary physico‐chemical integration of the material with living bone. Materials behaving in this way can be considered for potential biomedical application as bone tissue substitute for a natural bone repair or replacement as implant.A mechanism of hydroxyapatite formation on pseudowollastonite ceramics surface was investigated during exposure to a simulated body fluid (SBF) for a period of 3 weeks. Morphology and structure of the surface product and its original substrate was examined by thin‐film X‐ray diffraction, scanning electron microscopy and high‐resolution transmission electron microscopy. HA crystals were found to form on an amorphous silica intermediate layer. (100) lattice planes of HA were resolved and identified.Concentration of ions in the SBF and pH of the SBF were monitored throughout the exposure. Additional pH measurements were made at the interface of psW with SBF. The HA formation occurred when there was a sudden increase of pH from 7·25 to 10·5 at the interface of psW with SBF as a result of ionic exchange between 2H+and Ca2+within the psW network. This ionic exchange transformed the psW crystals into an amorphous silica phase. The appropriate pH and the ion concentrations were essential for partial dissolution of the amorphous silica phase and subsequent precipitation of a Ca‐P rich phase which then tra

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1996.tb04794.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

Observations made using AFM and SEM have been combined in order to study the structure of asphalts. Fluorescence microscopy was used to aid in understanding the structural changes occurring when polymer is added to the asphalts.  With the atomic force microscope we are able to study the structure of the asphalts without any pre‐preparation. Despite very low resolution, our study reveal ed a network of asphaltene molecules with regard to asphalt gel. The same result is obtained by SEM observation but with a much better resolution. SEM observation, however, needs an adequate preparation method.  In the presence of polymer we observed a rearrangement of the initial asphaltene association which leads to the assumption that polymer can aggregate the asphaltene

ISSN:0022-2720    

DOI:10.1046/j.1365-2818.1996.134416.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

SummaryFluorescencein situhybridization on human metaphase chromosomes is detected by near‐field scanning optical microscopy. This combination of cytochemical and scanning probe techniques enables the localization and identification of several fluorescently labelled genomic DNA fragments on a single chromosome with an unprecedented resolution. Three nucleic acid probes are used: pUC1. 77. p1–79 and the plasmid probe α‐spectrin. The hybridization signals are very well resolved in the near‐field fluorescence images, while the exact location of the probes can be correlated accurately with the chromosome topography as afforded by the shear for

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1996.tb04795.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

This work describes the use of two cationic porphyrins for fluorescent DNA counterstaining of HeLa cells also stained by means of indirect immunofluorescence with fluorescein isothiocyanate (FITC)‐conjugated secondary antibodies. Staining HeLa cells with meso‐tetra(4‐N‐methylpyridyl)porphine (T4MPyP) and meso‐tetra( p‐N‐trimethylanilinium)porphine (TMAP), both used at 5 × 10−6 m, gives rise to a deep red emission of chromatin from interphase nuclei and mitotic chromosomes when the cells are excited with blue (490 nm) light. The red‐fluorescing chromatin contrasted very well with the yellowish‐green emission from FITC‐immunofluorescent staining. No significant difference in chromatin fluorescence found with either T4MPyP or TMAP was detected. Counterstaining with the porphyrins could be carried out as a separate step after immunolabelling or, more simply, by their inclusion in the mounting medium. Spectral analysis demonstrated that the fluorescent emission maximum of T4MPyP was at 665 nm and that the intensity of the fluorescent emission showed a considera

ISSN:0022-2720    

DOI:10.1046/j.1365-2818.1996.114394.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

The wavelength dependence of the incoherent point spread function in a wide‐field microscope was investigated experimentally. Dispersion in the sample and optics can lead to significant changes in the point spread function as wavelength is varied over the range commonly used in fluorescence microscopy. For a given sample, optical conditions can generally be optimized to produce a point spread function largely free of spherical aberration at a given wavelength. Unfortunately, deviations in wavelength from this value will result in spherically aberrated point spread functions. Therefore, when multiple fluorophores are used to localize different components in the same sample, the image of the distribution of at least one of the fluorophores will be spherically aberrated. This aberration causes a loss of intensity and resolution, thereby complicating the localization and analysis of multiple components in a multi‐wavelength image. We show that optimal resolution can be restored to a spherically aberrated image by constrained, iterative deconvolution, as long as the spherical aberration in the point spread function used for deconvolution matches the aberration in the image reasonably well. The success of this method is essentially independent of the initial degree of spherical aberration in the image. Deconvolution of many biological images can be achieved by collecting a small library of spherically aberrated and unaberrated point spread functions, and then choosing a point spread function appropriate for deconvolving each image. The co‐localization and relative intensities of multiple components can then be accurately studied in a multi‐wavelengt

ISSN:0022-2720    

DOI:10.1046/j.1365-2818.1996.122402.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

We consider the effects of finite sized coherent and incoherent detectors on the axial resolution of confocal microscopes. We adopt a high‐angle vector approach which takes the polarization property of the object into account. We further consider polarization imaging and show that coherent detection has an advantage over incoherent detection in terms of the value of the extinction coefficient. The desirability of aberration correction is briefly discusse

ISSN:0022-2720    

DOI:10.1046/j.1365-2818.1996.129410.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

An observation of a Boolean model consists of a set of covered points. In the one‐dimensional discrete case, the likelihood function of an observation can be expressed via the lengths of sequences of covered points and points not covered, called black and white runlengths, respectively. The black and white runlengths are independent random variables whose respective distributions determine the one‐dimensional discrete Boolean model completely. Under certain conditions, a two‐dimensional discrete Boolean model induces a one‐dimensional discrete Boolean model, thereby allowing the likelihood function of a one‐dimensional observation to be expressed in terms of the parameters of the two‐dimensional model. This relationship enables maximum likelihood estimation to be performed on the two‐dimensional model using linear samples. Examples are given including an application involving micrographs of to

ISSN:0022-2720    

DOI:10.1046/j.1365-2818.1996.124405.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY