AUTORADIOGRAPHIC AND CYTOCHEMICAL EVIDENCE FOR SYNTHESIS OF A LYSINE-CONTAINING RIBONUCLEOPROTEIN IN NUCLEOLI INHIBITED BY ACTINOMYCIN D

Quantitative ultrastructural characterisation of rabbit erythroblasts and of 3H uridine incorporation into their nuclear components

Electron microscopic-autoradiographic and morphometric investigations were carried out in erythroblasts from rabbit bone marrow. 1. to obtain quantitative data for the erythroblast classes. 2. to determine quantitative-morphometrically the incorporation rate of 3H uridine into the cell components of the different erythroblast classes. 3. to evaluate the influence of UV irradiation on the incorporation of 3H uridine. According to ultrastructural criteria erythroblasts are divided into 3 classes: basophilic erythroblasts (BE), polychromatic erythroblasts (PE) and orthochromatic erythroblasts (OE). The areas of the 3 classes of erythroblasts are in a ratio of 1:0.5:0.43. In all classes the portion of the nucleus is between 56 and 58.8%. The portion of mitochondria decreases from 13.3% (BE) to 9.3% (PE), and to 6.3% (OE) respectively. Simultaneously the portion of heterochromatin in the nuclear area rises from 24.2% (BE) to 49.8% (PE), and to 63.2% (OE) whereas the percentage of euchromatin decreased correspondingly. Nucleoli were found only in 78% of the BE and in 3.4% of the PE. For the quantitative determination of the silver grains and silver filaments, respectively, the morphometric procedures have been adapted to the particular conditions. So it was necessary to estimate the areas covered by silver grains of filaments. The silver grains or filaments localised in the nuclear area are in the range from 84.6 to 93.4%. The percentage of silver grains of the total cellular area is 14.4% in BE, 6.8% in PE and 4% in OE. In a similar way the relative values of the nucleolus (total) and the euchromatin and heterochromatin are reduced. UV irradiation of bone marrow in vitro for 10 to 20 min does not cause any significant changes in the incorporation of 3H uridine. This result is in contrast to other published experiments on the influence of UV on the RNA synthesis. It is assumed that the irradiation dose was too low to induce a measurable effect on the RNA synthesis or the point of investigation was too early.

On the cytochemical demonstration of basic proteins in the cell nucleus, including the nucleolus

A combined Feulgen-alkaline fast green method is described for simultaneous demonstration of DNA and basic proteins in the cell nucleus. The method is based on preserving both types of substances in the tissue section and releasing in them reactive groups for the 2 kinds of staining. These conditions are best provided, as proved by staining tests on tissue hydrolysates, if formalin-containing mixtures (SERRA's or LILLIE's fluids) are employed for fixation, and cold 5 N HCl is used for FEULGEN hydrolysis. In this way, a good cytological picture is also achieved. Nuclear euchromatin stains with this method red, while heterochromatin, pycnotic nuclei and sperm heads exhibit a deep violet to blue-violet colour. Prominent nucleoli of metabolically active cells display a distinct blue-green staining thus manifesting their high content of basic proteins. Acetylation test reveals that these proteins are of lysine-rich type. The known negative reaction of the nucleoli with the routine alkaline fast green method according to ALFERT and GESCHWIND must be attributed to an extraction of the nucleolar basic proteins with the hot TCA used in this method. Certain analogy in the cytochemical behaviour between the nucleolous and the chromatin under various conditions of hydrolysis leads to the suggestion that the nucleolar basic proteins demonstrated should be in the form of a ribonucleoprotein complex, probably of the pre-ribosomal material of the nucleolus.

Effect of temperature of aldehyde fixation on the radioautographic localization of ribonucleoprotein in nucleoli of HeLa cells. Inhibition by puromycin and actinomycin D

In efforts to clarify the role of the nucleolus and substructures thereof in the assembly or synthesis of protein associated with formation of the complete ribosome, the effect of variation of some conditions of aldehyde fixation on the intranuclear distribution of lysine-(3)H, arginine-(3)H, and uridine-(3)H was studied by differential grain count in radioautographs of PPLO-free HeLa cells. It was found that the nucleolus is a site of rapid assembly or synthesis of a protein, the synthesis of which is inhibited equally by puromycin (200 microg/ml) and by actinomycin D under conditions inhibitory for ribosomal precursor RNA synthesis (P < 0.01). This protein is fixed by phosphate-buffered formalin or glutaraldehyde at pH 7.3, but the label is diminished by fixation in customarily employed acetic ethanol or in formalin at acid pH. Elevation of temperature of formalin or glutaraldehyde fixatives to 37 degrees C consistently reduces the nucleolar protein label, but not the RNA label, by a proportion identical with that incurred by puromycin or actinomycin inhibition. This proportional reduction of nucleolar protein label occurs without evident loss of total grain count and is independent of length of fixation between 30 min and 4 hr, but it is not observed at 23 degrees C. The data support the interpretation that the proportion of nucleolar protein not fixed at 37 degrees C is associated with nucleolar ribosomal RNA but that it is dissociated at 37 degrees C in formalin or glutaraldehyde fixatives, probably on the basis of ionic dissociation of a conjugated ribonucleoprotein.