Tritium and Phosphorus-32 in High-Resolution Autoradiography

Penetration, distribution, and elimination of remofuscin/soraprazan in Stargardt mouse eyes following a single intravitreal injection using pharmacokinetics and transmission electron microscopic autoradiography: Implication for the local treatment of Stargardt's disease and dry age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of blindness in older people in the developed world while Stargardt's disease (SD) is a juvenile macular degeneration and an orphan disease. Both diseases are untreatable and are marked by accumulation of lipofuscin advancing to progressive deterioration of the retinal pigment epithelium (RPE) and retina and subsequent vision loss till blindness. We discovered that a small molecule belonging to the tetrahydropyridoether class of compounds, soraprazan renamed remofuscin, is able to remove existing lipofuscin from the RPE. This study investigated the drug penetration, distribution, and elimination into the eyes of a mouse model for increased lipofuscinogenesis, following a single intravitreal injection. We measured the time course of concentrations of remofuscin in different eye tissues using high-performance liquid chromatography combined with mass spectroscopy (HPLC-MS). We also visualized the penetration and distribution of 3 H-remofuscin in eye sections up to 20 weeks post-injection using transmission electron microscopic (TEM) autoradiography. The distribution of silver grains revealed that remofuscin accumulated specifically in the RPE by binding to the RPE pigments (melanin, lipofuscin and melanolipofuscin) and that it was still detected after 20 weeks. Importantly, the melanosomes in choroidal melanocytes only rarely bind remofuscin emphasizing its potential to serve as an active ingredient in the RPE for the treatment of SD and dry AMD. In addition, our study highlights the importance of electron microscopic autoradiography as it is the only method able to show drug binding with a high intracellular resolution.

Quantification of cell-specific substrate uptake by probe-defined bacteria under in situ conditions by microautoradiography and fluorescence in situ hybridization

A technique based on quantitative microautoradiography (QMAR) and fluorescence in situ hybridization (FISH) was developed and evaluated in order to determine the quantitative uptake of specific substrates in probe-defined filamentous bacteria directly in a complex system. The technique, QMAR-FISH, has a resolution of a single cell and is based on an improved fixation protocol and the use of an internal standard of bacteria with known specific radioactivity. The method was used to study the in situ ecophysiology of the filamentous bacteria 'Candidatus Meganema perideroedes' and Thiothrix sp. directly in an activated sludge system. The cellular uptake rate of tritium-labelled substrates revealed an average cell-specific uptake rate of 4.1 yen 10-15 mol of acetate cell-1 h-1 and 3.1 yen 10-15 mol of acetate cell-1 h-1 for the two filamentous species respectively. The two filamentous species had very similar activity in all cells along each filament. Surprisingly, the filaments within both probe-defined populations had threefold variation in activity between the different filaments, demonstrating a large variation in activity level within a single population in a complex system. The substrate affinity (Ks) for uptake of acetate of the cells within the two filamentous bacteria was determined by incubation with variable concentrations of labelled acetate. The Ks values of the 'Candidatus Meganema perideroedes' and the Thiothrix filamentous bacteria were determined to be 1.8 micro M and 2.4 micro M acetate respectively.

The binding of oestradiol-17beta to human spermatozoa - an electron microscope autoradiographic study

The location of steroid binding sites with specificity for oestradiol-17beta at an ultrastructural level has been examined on human spermatozoa by electron microscope autoradiography. About 75% of the 438 gains produced by 3H-oestradiol-17beta, and counted on electron microscope autoradiographs, were found over the plasma membrane or within 1000 A of it. This study provides evidence suggesting that the plasma membrane is a site of action of oestradiol-17beta in human spermatozoa.

Production of cells without deoxyribonucleic acid during thymidine starvation of lexA- cultures of Escherichia coli K-12

When thymidine-requiring lexA- strains were starved for thymidine, the kinetics of survival were similar to those of a nearly isogenic lexA+ strain. The size distribution of cells in the lexA- and lexA+ cultures were, however, quite different. Whereas most of the cells in the starved lexA+ cultures grew into long filamentous forms (longer than 4.0 mum), many of the lexA- cells were found to have a normal rod shape (4.0 mum or shorter). It was shown that lexA- cells undergo more divisions during thymidine starvation than lexA+ cells. Furthermore, using an autoradiographic method to analyze deoxyribonucleic acid (DNA) distribution in the starved cells, we demonstrated that cells without DNA are produced in both normal and starved lexA- cultures at a much higher frequency than in lexA+ cultures. Some of these cells may be produced by breakdown of DNA, but we favor the hypothesis that they result from an abnormal cell division process. Since lexA mutations are dominant, we conclude that a diffusible product decreases the synthesis or activity of an inhibitor of cell division in lexA- strains when DNA synthesis is blocked by thymidine starvation.

Minicells of Bacillus subtilis

After nitrosoguanidine (N-methyl-N'-nitro-N-nitrosoguanidine) mutagenesis, two Bacillus subtilis mutants (div IV-A1 and div IV-B1) were isolated that are defective in the location of division site along cell length. Both mutations were transferred into strain CU403 by transformation, and their properties were studied in the CU403 genetic background. Location of divisions in close proximity to cell pole regions in both mutants results in minicell production. Purified minicells contain a ratio of ribonucleic acid to protein comparable to that found in the parent cells. Autoradiographs of (3)H-thymine incorporation into deoxyribonucleic acid (DNA), thymine-2-(14)C incorporation into DNA, electron micrographs, and chemical analyses for DNA all fail to demonstrate DNA in the minicells. Minicells produced by both mutants are highly motile, an indication of functional energy metabolism. Electron micrographs reveal that minicells are produced by a structurally normal division mechanism and that minicells contain a normal cell surface. The div IV-A1 mutation has been mapped by PBS1 transduction linked to ura. The div IV-B1 mutation is closely linked to pheA by both PBS1 transduction and by co-transformation.

Genetic regulation of cell division initiation in Bacillus subtilis

The growth and division properties of a temperature-sensitive mutant of Bacillus subtilis defective in the initiation of cell division have been studied. Log-phase cells transferred from 30 to 45 C continue to increase in length but fail to initiate new divisions. Deoxyribonucleic acid synthesis continues at 45 C, and genomes are segregated along the filament length. When filaments are returned to 30 C, division initiation resumes, and the long multinucleate clones are partitioned into normal-size cells. Occasionally, multiple cross walls initiate in close proximity, resulting in tiny cells, some of which are anucleate. Division resumption is sensitive to protein synthesis inhibitors, suggesting there is a new protein required for the initiation of division in filaments.

Deoxyribonucleic acid distribution in Bacillus subtilis independent of cell elongation

A temperature-sensitive DNA(-) mutant of Bacillus subtilis has been studied during the resumption of deoxyribonucleic acid (DNA) synthesis following a 45 to 30 C temperature shift. For several hours after return to 30 C, DNA synthesis proceeds although the cells fail to elongate appreciably. Autoradiographs of cell populations synthesizing DNA during the recovery period demonstrate that DNA can become distributed to previously unoccupied regions along the cell length. By varying the labeling regime, newly synthesized DNA as well as DNA present at the time of transfer from 45 to 30 C were followed independently. Measurements of the percent of cell length covered by grains ((3)H-thymine in DNA) demonstrate the progressive refilling of DNA-vacant cell regions by both newly synthesized and original DNA. These data indicate that cell surface growth is not an absolute requirement for segregation of bacterial DNA.

On the process of cellular division in Escherichia coli. VI. Use of a methocel-autoradiographic method for the study of cellular division in Escherichia coli

A technique allowing chain formation by Escherichia coli for the analysis of the segregation of certain cellular components by autoradiographic methods has been developed. Deoxyribonucleic acid labeled with (3)H-thymidine does not appear to segregate preferentially with one or another of the bacteria. Membrane lipids labeled with either (3)H-oleate or (3)H-glycerol are evenly distributed among all progeny cells. A similar pattern of distribution of cell wall material is observed when (3)H-diaminopimelate is used as the marker.

Uranium localization on hydroxyapatite by analysis of fission fragment tracks

The distribution of enriched uranium on individual hydroxyapatite crystals after an exchange reaction has been investigated by means of thermal neutron irradiation followed by electron microscopic analysis of fission fragment tracks in plastic support films. One uranyl ion for every two to three surface calcium ions became associated with the mineral but in a nonuniform distribution that strongly favors crystal end regions.

Resolution in electron microscope radioautography

An analysis of grain distributions around a radioactive line source (consisting of polystyrene-(3)H) showed that the shape of the distribution was independent of the factors that influence resolution, i.e. section and emulsion thickness, silver halide crystal, and developed grain size. These factors did effect the spread of the distribution, however, and thus the distance from the line source within which 50% of the total developed grains fell. We called this distance "half distance" (HD) and determined it for a variety of specimens. When grain distributions were normalized in units of HD, one could plot universal grain distributions for specimens with radioactive sources of various shapes. The use of HD and the universal curves in interpreting radioautograms is discussed.

Absolute sensitivity of electron microscope radioautography

A calibration method is described for measuring absolute radioautographic sensitivities under various experimental conditions. Sensitivities to (3)H and (35)S radiation, i.e. ratio of developed grains to radioactive decays in the specimen, were determined with Ilford L4 and Kodak NTE emulsions. The highest values obtained in monolayers of emulsion were (1/8) for (3)H and 1/21 for (35)S. The influence of various experimental parameters on sensitivity is described, and the possibilities for quantitative electron microscope radioautography are discussed.