Light microscope based analysis of three-dimensional structure: applications to the study of Drosophila salivary gland nuclei. II. Algorithms for model analysis

Reconstruction and display of curvilinear objects from optical section data using 3-D curve fitting algorithms

Biological objects resembling filaments are often highly elongated while presenting a small cross-sectional area. Examination of such objects requires acquisition of images from regions large enough to contain entire objects, but at sufficiently high resolution to resolve individual filaments. These requirements complicate the application of conventional optical sectioning and volume reconstruction techniques. For example, objective lenses used to acquire images of entire filaments or filament networks may lack sufficient depth (Z) resolution to localize filament cross-sections along the optical axis. Because volume reconstruction techniques consider only the information represented by a single volume element (voxel), views of filament networks reconstructed from images obtained at low Z-resolution will not accurately represent filament morphology. A possible solution to these problems is to simultaneously utilize all available information on the path of an object by fitting 3-D curves through data points localized in 2-D images. Here, we present an application of this approach to the reconstruction of microtubule networks from 2-D optical sections obtained using confocal microscopy, and to synthesized curves which have been distorted using a simple mathematical model of optical sectioning artefacts. Our results demonstrate that this strategy can produce high resolution 3-D views of filamentous objects from a small number of optical sections.

Temporal and spatial coordination of chromosome movement, spindle formation, and nuclear envelope breakdown during prometaphase in Drosophila melanogaster embryos

The spatial and temporal dynamics of diploid chromosome organization, microtubule arrangement, and the state of the nuclear envelope have been analyzed in syncytial blastoderm embryos of Drosophila melanogaster during the transition from prophase to metaphase, by three-dimensional optical sectioning microscopy. Time-lapse, three-dimensional data recorded in living embryos revealed that congression of chromosomes (the process whereby chromosomes move to form the metaphase plate) at prometaphase occurs as a wave, starting at the top of the nucleus near the embryo surface and proceeding through the nucleus to the bottom. The time-lapse analysis was augmented by a high-resolution analysis of fixed embryos where it was possible to unambiguously trace the three-dimensional paths of individual chromosomes. In prophase, the centromeres were found to be clustered at the top of the nucleus while the telomeres were situated at the bottom of the nucleus or towards the embryo interior. This polarized centromere-telomere orientation, perpendicular to the embryo surface, was preserved during the process of prometaphase chromosome congression. Correspondingly, breakdown of the nuclear envelope started at the top of the nucleus with the mitotic spindle being formed at the positions of the partial breakdown of the nuclear envelope. Our observation provide an example in which nuclear structures are spatially organized and their functions are locally and coordinately controlled in three dimensions.

Fluorescence microscopy in three dimensions

The combination of the specificity provided by fluorescence microscopy and the ability to quantitatively analyze specimens in three dimensions allows the fundamental organization of cells to be probed as never before. Key features in this emergent technology have been the development of a wide variety of fluorescent dyes or fluorescently labeled probes to provide the requisite specificity. High-quality, cooled charge-coupled devices have recently become available. Functioning as nearly ideal imagers or "electronic film," they are more sensitive than photomultipliers and provide extraordinarily accurate direct digital readout from the microscope. Not only is this precision crucial for accurate quantitative imaging such as that required for the ratioing necessary to determine intracellular ion concentrations, but it also opens the way for sophisticated image processing. It is important to realize that image processing isn't simply a means to improve image aesthetics, but can directly provide new, biologically important information. The impact of modern video microscopy techniques (Allen, 1985; Inoué, 1986) attests to the fact that many biologically relevant phenomena take place at the limits of conventional microscopy. Image processing can be used to substantially enhance the resolution and contrast obtainable in two dimensions, enabling the invisible to be seen and quantitated. Cells are intrinsically three-dimensional. This can simply be a nuisance because of limited depth of focus of the microscope or it could be a fundamental aspect of the problem being studied. In either case, image processing techniques can be used to rapidly provide the desired representation of the data. In this chapter we have discussed the nature of image formation in three dimensions and dealt with several means to remove contaminating out-of-focus information. The most straightforward of these methods uses only information from adjacent focal planes to correct the central one. This approach can be readily applied to virtually any problem and with most commonly available image processing hardware to provide a substantially deblurred image in almost real time. In addition to covering more sophisticated algorithms where the utmost in three-dimensional imaging is required, we have developed a method for extremely rapidly and accurately producing an in-focus, high-resolution "synthetic projection" image from a thick specimen. This is equivalent to that produced by a microscope having the impossible combination of a high-NA objective lens and an infinite depth of focus. A variation on this method allows efficient calculation of stereo pairs.(ABSTRACT TRUNCATED AT 400 WORDS)

Microscopic imaging of cells

The microworld was revealed to investigators through a glass bead or a hanging water droplet long before optics was understood. The cellular structure of plants was well resolved by such simple magnifying glasses, van Leeuwenhoek, the Dutch merchant and amateur microscopist, was the first to report to the English Royal Society his observations of bacteria with his single-lens microscope in 1665.

The use of a charge-coupled device for quantitative optical microscopy of biological structures

The properties of a charge-coupled device (CCD) and its application to the high-resolution analysis of biological structures by optical microscopy are described. The CCD, with its high resolution, high sensitivity, wide dynamic range, photometric accuracy, and geometric stability, can provide data of such high quality that quantitative analysis on two- and three-dimensional microscopic images is possible. For example, the three-dimensional imaging properties of an epifluorescence microscope have been quantitatively determined with the CCD. This description of the imaging properties of the microscope, and the high-quality image data provided by the CCD, allow sophisticated computational image processing methods to be used that greatly improve the effective resolution obtainable for biological structures. Image processing techniques revealed fine substructures in Drosophila embryonic diploid chromosomes in two and three dimensions. The same approach can be extended to structures as small as yeast chromosomes or to other problems in structural cell biology.

Fluorescence digital imaging microscopy in cell biology

Developments in microscope, sensor, and image-processing technologies have led to integrated systems for the quantification of low-light-level emission signals from biological samples. Specificity is provided in the form of monoclonal antibodies and other ligands or enzyme substrates conjugated with efficient fluorophores. Fluorescent probes are also available for cellular macromolecular constituents and for free ions of biological interest such as H+ and Ca2+. The entire spectrum of photophysical phenomena can be exploited. Representative data are presented from studies of DNA conformation and architecture in polytene chromosomes and from studies of receptor-mediated endocytosis, calcium distribution, and the organization of the contractile apparatus in muscle cells.