Coating sections for electron microscopic autoradiography: a stripping technique using liquid emulsion

Downregulation of KRC induces proliferation, anchorage independence, and mitotic cell death in HeLa cells

The large zinc finger protein KRC regulates transcription of target genes via the kappaB gene enhancer element. As an attempt to investigate the cellular function of KRC, we have established cell lines stably transfected with KRC expression vectors. Introduction of a vector directing expression of a transcript antisense to KRC mRNAs in several mammalian cell lines resulted in accelerated proliferation. Furthermore, in HeLa cells, downregulation of KRC conferred anchorage-independent growth and promoted cell cycle progression without an intervening cytokinesis, culminating in the formation of multinucleated giant cells. Ultimately these cells died.

Lesions and preferential initial localization of [S-methyl-3H]bleomycin A2 on Saccharomyces cerevisiae cell walls and membranes

Extensive lesions were produced in cell walls of Saccharomyces cerevisiae by the bleomycin family of anticancer antibiotics (30 min to 4 h). Electron micrographs revealed that the alterations were most frequently large breaks and small interruptions or holes in cell walls, which sometimes extended into cell membranes. Large portions of cell walls were sometimes lost. Cell walls were frequently ruptured in one or more positions. More than 75% of bud scar regions in single-plane sections and all bud scars in serial sections exhibited many interruptions and breaks after 3 or 4 h of treatment. The discovery of extensive damage to cell walls was consistent with the preferential (approximately 70%) association of radiolabeled bleomycin with cell walls and perimeters of bud scar regions after short exposures (30 min). After longer exposures, the distribution of silver grains changed from a predominant association with cell walls (30 min) to an increased association with the cell cytoplasm (1 to 4 h). This correlated with increased ultrastructural damage, since damage to cell walls was generally more frequent and more severe with increasing length of treatment (30 min to 4 h) or dose (25 to 100 micrograms/ml). Although DNA lesions are believed to be the lethal properties of bleomycins, the lesions produced in cell walls are also lethal properties of the antibiotics. The distributions of lesions on cell walls suggested a generalized interaction of the antibiotic with a cell wall component. These results led us to hypothesize a mechanism of effective antifungal action for the bleomycin family of antibiotics.

The distribution and synaptic organization of serotoninergic elements in the inferior olivary complex of the opossum

Immunohistochemistry and high-resolution autoradiography were used to analyze the distribution and synaptic organization of serotonin (5HT) - containing elements in the inferior olivary complex of the opossum. Immunoreactive beaded varicosities are present throughout the olivary complex. The densest 5HT immunostaining is present in subnucleus b of the caudal medial accessory nucleus. The rostral principal olive is sparsely populated with immunoreactive elements. Fine beaded fibers arborize throughout the neuropil of all the olivary nuclei except in subnucleus b of the caudal medial accessory nucleus where they also circumscribe neuronal cell bodies. In addition, a distinct population of large beaded fibers are occasionally encountered in the neuropil of the medial accessory nucleus. Ultrastructurally, labeled profiles that correspond in size to the smaller beads (less than 1 micron) contain tubulovesicular elements, large dense-cored vesicles, and clear vesicles. In contrast, larger profiles (greater than 2 microns) are characterized by numerous clear synaptic vesicles. Synaptic junctions were encountered in only 2% of the labeled elements. The majority of the labeled profiles were in juxtaposition to small-diameter dendrites (less than 2 microns) except in the caudal medial accessory nucleus, where they also were found in apposition to olivary cell bodies. Our results, when compared with other accounts, indicate that rather than major differences in the nuclear distribution of serotonin between species, there are differences in the density of serotoninergic elements in specific nuclei of the mammalian inferior olive. Based on the size of the labeled profiles and the distinct vesicle populations, our data suggest there are at least two populations of 5HT varicosities that are in juxtaposition to olivary neurons. Further, boutons containing 5HT primarily interact with the distal dendrites of olivary neurons except in the caudal medial accessory nucleus where cell bodies are in apposition to 5HT varicosities.

An improved method for combined autoradiography and histochemistry: the simultaneous detection of 6-3H thymidine and acid phosphatase activity in cryostat sections of mouse thymus and duodenum

A new method is described that enables the simultaneous detection of 6-3H thymidine incorporation and acid phosphatase activity in the same tissue section. Histochemically, naphthol AS B1 released by tissue based acid phosphatase activity from the substrate naphthyl AS B1 phosphoric acid is coupled with a range of diazonium salts to produce insoluble azo dyes. The azo dye tests result in a particulate localization of lysosomal acid phosphatase and also label diffuse sources associated with cell death. The tests selected permit the application of photographic emulsion without the necessity of an inert barrier layer to separate the emulsion from the histochemically treated cryosections. The localization of 6-3H thymidine incorporation and cell death in mouse thymus and duodenum is demonstrated and comparative counts estimating the distribution of 6-3H thymidine incorporation and hydrolase labelled cell death in the thymus are presented. Young mouse thymus (5 weeks) was found to contain 1.36 +/- 0.12% dying cells and 6.78 +/- 0.03% thymidine incorporating cells, whilst old mouse thymus (53 weeks) was found to contain 2.34 +/- 0.6% dying cells and 5.29 +/- 0.37% thymidine incorporating cells.

A unit density method of grain analysis used to identify GABAergic neurons for electron microscopic autoradiographs

The distribution of electron microscopic autoradiographic grains over neurons in cerebellar cultures incubated with [3H]gamma-aminobutyric acid ([3H]GABA) was examined. With the unit density method of grain analysis, the number of grains over each structure was tested against the total grain density for the entire section. If an individual structure has a grain density higher than the expected grain density, it is considered one of the group of heavily labeled structures. The expected grain density for each structure is calculated based on the area for that structure, the total grain density and the Poisson distribution. A different expected grain density can be calculated for any P value required. The method provides an adequate population of structures for morphological analysis but excludes weakly labeled structures and thus may underestimate the number of labeled structures. The unit density method of grain analysis showed, as expected, a group of cell bodies and synapses that was labeled heavily. Cultures incubated with other [3H]amino acids did not have any heavily labeled synaptic elements. In addition, serial section analysis of sections showed that synapses heavily labeled with [3H]GABA are seen in adjacent section. The advantage of the unit density method of grain analysis is that it can be used to separate two groups of metabolically different neurons even when no morphological differences are present.

An alternative to the flat substrate method of preparing electron microscope autoradiographs

Difficulty with flat substrate methods of preparing electron microscope autoradiographs has prompted reconsideration and refinement of a technique in which an electron microscope grid is placed beneath the specimen prior to dipping. This technique avoids the problems commonly associated with the direct application of emulsions to specimen grids, and should be considered as an alternative to flat substrate techniques when difficulty with these methods is encountered.

Freeze-drying of unfixed monolayer cultures for electron microscopic autoradiography

A method has been developed for freezing, drying and embedding of unfixed monolayer cultures for electron microscopic autoradiography (EM ARG). Experimental results showed: a) Aclar 33 C was a more suitable substrate than the plastic of petri dishes, b) cultures pressed rapidly against the polished face of a large copper cylinder chilled in liquid nitrogen had better cellular morphology than did cultures dipped in Freon 12 chilled in liquid nitrogen, and c) cultures embedded in Epon alone had finer extracellular ice spaces and lower background grain densities than did cultures embedded in Epon with 1% silicone. This method has been used to evaluate the effect of fixation on the localization of the neurotransmitter, 3H-gamma-aminobutyric acid (3H-GABA), in neurons of dispersed cell cultures. EM ARG results showed that the neuronal cell bodies and vesicle elements were present in similar numbers in both glutaraldehyde fixed and freeze-dried cultures.

Electron microscopic autoradiography of the uptake of [3H]GABA in dispersed cell cultures of rat cerebellums. I. The morphology of the GABAergic synapse

Dispersed cell cultures of rat cerebellums 21 days in vitro were incubated in saline containing 0.5 micrometer [3H]GABA for 5 min, fixed and prepared for electron microscopic autoradiography. Quantitative methods for analyzing the resulting autoradiographs were developed to distinguish lightly labeled neurons from heavily labeled (i.e. GABAergic) neurons. After a 3 week exposure, 2% of the presynaptic elements were found to be GABAergic. A longer incubation time of 15 min resulted in a greatly increased grain density over lightly labeled neurons, making it more difficult to distinguish them from the GABAergic neurons. When the concentration of [3H]GABA was increased to 1.0 micrometer, the grain densities over both GABAergic and other neurons increased to a similar extent. The morphology of the GABAergic synapses differed from that of the total population synapses. The GABAergic synapses had larger cross-sectional areas, lower densities of vesicles, greater numbers of vesicles, and thinner postsynaptic densities. Both the GABAergic and total population had similar lengths of the postsynaptic densities, cleft widths, vesicle sizes and types of postsynaptic elements. The morphology of the GABAergic synapse reported here is similar to that described for basket and stellate presynaptic elements in vivo.