Image intensification techniques for detection of proteins in cultured cells

Robert Feulgen Prize Lecture 1995. Electronic light microscopy: present capabilities and future prospects

Electronic light microscopy involves the combination of microscopic techniques with electronic imaging and digital image processing, resulting in dramatic improvements in image quality and ease of quantitative analysis. In this review, after a brief definition of digital images and a discussion of the sampling requirements for the accurate digital recording of optical images, I discuss the three most important imaging modalities in electronic light microscopy--video-enhanced contrast microscopy, digital fluorescence microscopy and confocal scanning microscopy--considering their capabilities, their applications, and recent developments that will increase their potential. Video-enhanced contrast microscopy permits the clear visualisation and real-time dynamic recording of minute objects such as microtubules, vesicles and colloidal gold particles, an order of magnitude smaller than the resolution limit of the light microscope. It has revolutionised the study of cellular motility, and permits the quantitative tracking of organelles and gold-labelled membrane bound proteins. In combination with the technique of optical trapping (optical tweezers), it permits exquisitely sensitive force and distance measurements to be made on motor proteins. Digital fluorescence microscopy enables low-light-level imaging of fluorescently labelled specimens. Recent progress has involved improvements in cameras, fluorescent probes and fluorescent filter sets, particularly multiple bandpass dichroic mirrors, and developments in multiparameter imaging, which is becoming particularly important for in situ hybridisation studies and automated image cytometry, fluorescence ratio imaging, and time-resolved fluorescence. As software improves and small computers become more powerful, computational techniques for out-of-focus blur deconvolution and image restoration are becoming increasingly important. Confocal microscopy permits convenient, high-resolution, non-invasive, blur-free optical sectioning and 3D image acquisition, but suffers from a number of limitations. I discuss advances in confocal techniques that address the problems of temporal resolution, spherical and chromatic aberration, wavelength flexibility and cross-talk between fluorescent channels, and describe new optics to enhance axial resolution and the use of two-photon excitation to reduce photobleaching. Finally, I consider the desirability of establishing a digital image database, the BioImage database, which would permit the archival storage of, and public Internet access to, multidimensional image data from all forms of biological microscopy. Submission of images to the BioImage database would be made in coordination with the scientific publication of research results based upon these data.(ABSTRACT TRUNCATED AT 400 WORDS)

A fluorescent residualizing label for studies on protein uptake and catabolism in vivo and in vitro

Residualizing labels are tracers which remain in lysosomes after uptake and catabolism of the carrier protein and have been especially useful for studies on the sites of plasma protein degradation. Thus far these labels have contained radioactive reporters such as 3H or 125I. In the present paper we describe a fluorescent residualizing label, NN-dilactitol-N'-fluoresceinylethylenediamine (DLF). Modification of asialofetuin (ASF) or rat serum albumin (RSA) with DLF affected neither their normal kinetics of clearance from the rat circulation nor their normal tissue sites of uptake and degradation. After injection of DLF-ASF, fluorescent degradation products were recovered nearly quantitatively in liver and retained with a half-life of about 2 days. Fluorescent degradation products from DLF-RSA were recovered in skin and muscle, and were localized in fibroblasts by fluorescence microscopy. These results confirm previous studies with radioactive residualizing labels in which fibroblasts in peripheral tissues were identified as primary sites of albumin degradation. Fluorescent catabolites also accumulated in fibroblasts incubated with DLF-RSA in vitro, and residualized with a half-life of about 2 days. Overall, the data establish that DLF functions efficiently as a fluorescent residualizing label both in vivo and in vitro. The advantages of fluorescent, compared with radioactive, residualizing labels should make them valuable tools for studies on protein uptake and catabolism in biological systems.

Illumination and detection systems for quantitative fluorescence microscopy

Systems are described for the illumination and detection of light microscope images of fluorescence in living cells at low levels of excitation. The illumination system is based on the use of an acousto-optic modulator to control the wavelength and power of the excitation beam. The detection system utilizes an image intensifier coupled with a television camera to acquire images at extremely low intensities. Both the illumination and detection systems have superior performance compared to existing devices.

A temperature controlled chamber to allow observation and measurement of uptake of fluorochromes into live cells

A temperature controlled cell chamber is described which permits phase-contrast and fluorescence microscopy of living cells. It is shown how the cellular uptake of fluorochromes can be investigated both photographically and photometrically. Some sample results are presented for the uptake of Evans Blue.

Sudden volume changes of the lumen of inverted thyroid follicles in suspension cultures. Use in estimation of rates of water flux through thyroid epithelium

Inverted thyroid follicles in suspension culture were observed using dark-field illumination and time-lapse video enhancement techniques. The lumens of many follicles undergo episodes of rapid shrinkage followed by relatively slow dilation. The extent of shrinkage ranged from 10 to 40% of the initial diameter. The decrease in lumen diameter is accompanied by loss of luminal fluid. The rate of efflux of fluid amounted to from 1 to 90 microns3/micron2 of luminal surface/min. This was followed after several minutes by a slow and generally linear increase in lumen diameter with time that could be accounted for by an influx of fluid of the order of 0.5 micron3/micron2/min. It is possible that this phenomenon is due to a continued influx of fluid into the lumen until a junction opens between cells allowing a sudden loss of luminal fluid. The junction reseals and fluid begins to accumulate in the lumen. The phenomenon may be a three-dimensional analogue of the behavior of domes.

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.

Direct observation of the rapid aggregation of acetylcholine receptors on identified cultured myotubes after exposure to embryonic brain extract

We have directly observed the redistribution of acetylcholine receptors (AChR) on the surface of cultured myotubes, induced by a soluble brain extract. The AChR were fluorescently labeled with rhodamine-conjugated alpha-bungarotoxin and viewed under low incident illumination with a video image intensification system. The results of our sequential observations indicate that AChR aggregates can be assembled rapidly (30-120 min) from mobile, diffuse AChR. This assembly was characterized by the initial formation of microaggregates (less than 1 micron diameter) that increased in number and coalesced or grew to form larger aggregates. The redistribution of fluorescently labeled AChR was completely inhibited by illumination of cells at levels used for conventional fluorescence micrography and could be observed only by using low light levels.