A model of the breakdown and removal of the chromatin components during Feulgen acid hydrolysis

Standardization of the Feulgen-Schiff technique. Staining characteristics of pure fuchsin dyes; a cytophotometric investigation

Four fuchsin analogues (Pararosaniline, Rosaniline. Magenta II and New Fuchsin) usually found in Basic Fuchsin have been applied as chemically pure dyes to the Feulgen-technique. Total nuclear absorption and wavelength of the absorption maximum were measured by microspectrophotometry in Feulgen stained cytological and plastic embedded histological liver samples, and in lymphocyte nuclei in human peripheral blood smears; absorption spectra of Feulgen stained DNA-polyacrylamide films were determined by spectrophotometry. The grey value distribution of tetraploid liver cell nuclei was calculated with an image analyzer. The staining characteristics of the pure dyes were compared to commercial fuchsin samples from various suppliers. Reverse phase thin layer chromatography was used for characterization and qualitative separation of commercial batches. Pure fuchsin analogues were all equally suitable for Feulgen staining: with respect of staining intensity all pure fuchsin dyes gave nearly identical results with a bathochromic shift of the absorption maximum from Pararosaniline to New Fuchsin of about 8 microns. Differences in staining results observed among the commercial dyes were due to varying dye content, contamination with an acridine-like fluorescent compound or simply mislabelling of samples. Pure Pararosaniline is recommended for a standard Feulgen technique.

Lability to acid hydrolysis in some different DNA-protein complexes of spermatozoa

The Feulgen hydrolysis kinetics was investigated in spermatozoa with different composition in DNA-protein complexes. The species used were: Bos taurus (arginine rich nuclear protein also containing cystine residues), Pichroplus bergi, Triatoma infestans (arginine-rich nuclear protein), Lytechinus variegatus and Apis mellifera (lysine-rich nuclear protein). The spermatozoa were subjected to Feulgen's reaction, after varying the fixative type and the hydrolysis times. Feulgen-DNA values were obtained with an automatic scanning cytophotometric procedure. Differences were demonstrated in the hydrolysis kinetics as a function of differences in composition of the DNA-protein complexes being present in the spermatozoon chromatin. Differences in the profiles of Feulgen hydrolysis curves, having for basis the fixation, were rather clear for bull, grasshopper, and blood-sucking insect spermatozoa than for the sea-urchin and bee spermatozoa. The different hydrolysis kinetics of chromatin of blood-sucking insect spermatozoa compared to that of grasshopper, sea-urchin, and bee sperm cells suggests that, although the first 2 materials contain an arginine-rich "germinative" protein and the latter 2 ones contain a lysine-rich protein, these differ to each other. The DNA depurination was obtained more quickly for T. infestans (20 min) and P. bergi (10 min) spermatozoa when they were fixed in the ethanol-acetic acid (EA) mixture. Morphologically anomalous bull spermatozoa fixed in the EA mixture presented a quicker depurination (30 min) as compared to the normal cells (1 h). The fast lability to acid hydrolysis in the abnormal cells is certainly due to anomalies in their basic nuclear "germinative" protein. In the formalin fixed materials the maximal depurination was obtained earlier in bull spermatozoa (30 min) followed by sperm cells of P. bergi, T. infestans, L. variegatus (all of them one-hour hydrolysis) and finally Apis mellifera (2 h hydrolysis). The presence of secondary peaks at the descending branch of the hydrolysis curves of grasshopper and sea-urchin spermatozoa, indicates for these, more than 1 kind of apurinic-acid protein complexes. The spermatozoa bearing arginine-and/or cystine-rich nuclear protein contain a more easily soluble apurinic acid protein complex. Due to the differences in hydrolysis kinetics of chromatin in spermatozoa containing different nuclear "germinative" proteins, this cellular type does not appear indicated as a haploid control for evaluation of Feulgen-DNA contents of diploid and polyploid somatic cells.

Absorption spectrum of Feulgen-stained polytene chromosomes of Drosophila melanogaster

Hetero- and euchromatic polytene chromosome regions of early and fully grown larvae of Drosophila melanogaster had their Feulgen absorption curves determined cytophotometrically. Hydrolysis conditions adequate to induce maximal DNA depurination were used. No differences in curve shapes specially concerning the absorption shoulder at the 520 less than or equal to lambda less than or equal to 550 nm spectral range were detected with advancing polytenization or when comparing the absorption patterns for the hetero- and euchromatic regions to each other. It is considered that prominence of the Feulgen absorption shoulder could be related to the amount of Schiff molecules di-substituted with apurinic acid aldehydes and to the relatively larger resistance of these apurinic acid fragments towards solubilization with acid hydrolysis due to their binding to nuclear proteins. It is therefore assumed that no significant differences owing to the above-cited factors exist for the chromosome regions analyzed at 2 phases of the polytenization process. Consequently, the replication of reiterated sequences from the main band DNA which occurs in polytene chromosome regions of Drosophila melanogaster appears not to affect the Feulgen absorption spectrum of this material.

Comparative studies of Feulgen hydrolysis for DNA. I. Influence of different fixatives and polyethylene glycols

We compared the Feulgen hydrolysis curves (37 degrees C, 5 M HCl) of human blood lymphocytes fixed by the following four methods: 96% ethanol, 60 min at 20 degrees C; ethanol-acetone, 1:1, 120 min at 4 degrees C; ethanol-glacial acetic acid mixture (3:1), containing 2% of formaldehyde (EAF), 90 min at 20 degrees C; and ethanol-glacial acetic acid (3:1), 60 min followed by 5% chrome alum solution for 360 min at 20 degrees C. The best results were obtained with EAF-fixation, with respect to the highest amount of DNA-Schiff complex at the peak point of the curve, the longest "plateau" region and the smallest scattering of DNA-Schiff amount values along the "plateau". With other types of fixation the addition of polyethylene glycol (PEG) 6,000 to the hydrolysis solution resulted in modification of the shape of the hydrolysis curve so that it became nearly similar to the EAF-curve. The effect of PEG6000 on the EAF-curve was minimal. Slides fixed by ethanol were used for a comparison of polyethylene glycols with m.w. 1,500, 6,000 and 20,000. The longest "plateau" was obtained with PEG6000. The only effect of PEG1500 was a dramatic increase of DNA-Schiff amount at the peak point. PEG20000 had no significant effect on the shape of the hydrolysis curve. The results are discussed in terms of Kjellstrand's "chain with a stable structure" model of Feulgen hydrolysis.

Acid lability of deoxyribonucleic acids of some polytene chromosome regions of Rhynchosciara americana

An analysis of profiles of Feulgen hydrolysis curves has been carried out in two heterochromatic (B-15 and C-11) and one euchromatic (C-1) regions of polytene chromosomes of salivary glands of 66 day old Rhynchosciara americana larvae. Differences among these three regions have been found mostly concerning the period of predominant apurinic acid breakdown including the "lag" phase of teh apurinic acid depolymerization. The hydrolysis time for which maximal Feulgen-DNA values are attained also differs when comparing the hetero- and euchromatic regions of the C chromosome and the heterochromatic regions C11 and B15 to each other. Different labilities of DNA to acid hydrolysis have therefore been demonstrated for these chromosome regions. This has been tentatively correlated with differences in non-histone proteins some of which are assumed to be involved in chromatin compactness. Others (probably not concerned with chromatin compactness) are suggested to be associated with certain specific DNA types which are known to occur in these chromosome regions.

Feulgen-DNA absorption curves of polytene chromosome regions of Rhynchosciara americana

Feulgen absorption spectra of polytene chromosome regions, differing in types of DNA composition and of chromatin compactness, were determined microspectrophotometrically in squashed salivary glands of Rhynchosciara americana. The absorption curves exhibited a secondary maximum at their ascending branch after the chromatins were maximally depurinated. The degree of shoulder prominence could not be specifically correlated with the packing state or even with richness in satellite repetitive DNA of the chromatins. It is assumed that other factors may exist which play a part in the phenomenon that gives rise to the Feulgen absorption shoulder characteristics. Differences in the extraction rate of the apurinic acid fragments due to their binding to specific non-histone proteins are suggested as contributing to the above-mentioned absorption patterns when comparing the various chromatin types.

Mechanisms of the Feulgen acid hydrolysis

Our present knowledge of the two main reactions responsible for the form of the Feulgen hydrolysis curve is summarized. A suggestion that hydrolysis slightly above room temperature and in 5 M HCl is preferable is made and discussed. A formula making it possible to calculate the appropriate hydrolysis time at any normally used acid concentration and temperature is presented.

Quantitative aspects of the cytochemical Feulgen-DNA procedure studied on model systems and cell nuclei

Quantitative aspects of DNA losses during fixation and pararosaniline(SO2)-Feulgen staining of microscopic preparations were studied. The preparation of a new cytochemical model, consisting of DNA-protein layers (with thicknesses between 0.1 and 5.0 micrometer) on microscopic glass slides is described and potentialities and limitations of this model are discussed. Polyacrylamide films into which high molecular weight calf thymus DNA or chicken erythrocyte nuclei had been constrained served as another model. As biological objects chicken erythrocyte nuclei and rat liver nuclei either in suspension or on microscopical glass slides were used. The experimental results indicate a loss of about 5% of the DNA due to the fixation procedure applied. Hydrolysis in 5 N HCl at room temperature, staining with the pararosaniline-Schiff medium and rinsing with sulfurous acid induced losses of DNA too, varying in amount depending on the type of preparation used. About 10% of the original DNA content is lost in total from chicken erythrocyte nuclei and rat liver nuclei dried on microscopical glass slides, from chicken erythrocyte nuclei constrained in polyacrylamide films, and from DNA-protein layers on microscopic glass slides. For nuclei fixed and stained in suspension the total losses amount to about 40%. The differences in losses between various types of preparations are discussed. Biochemically, the content of DNA originally present per chicken erythrocyte nucleus was determined to be 2.52 pg, a value, which is in good accordance with reliable biochemical data published already. It is shown that calibration of cytochemical staining intensities into biochemical units or absolute amounts of material by use of a model system, is only reliable when it is known or to be expected that both the loss of material due to fixation and staining, and the stoichiometric relation between material present and dye molecules is identical. The same holds for the application of internal biological reference systems.

The effect of sodium chloride on the extraction of DNA fragments during Feulgen acid hydrolysis

Feulgen acid hydrolysis was performed on ascites tumour cells labelled with radioactive DNA-precursors. The development of fragments of apurinic acid and the extraction of purines were studied by monitoring the variations in the extraction rate during the hydrolysis when sodium chloride was either present or absent from the hydrolysis solution. The changes in the rate of extraction of purines and the alterations in the initial retardation of the apurinic acid extracting process followed approximately the same pattern. The extractability of apurinic acid fragments during hydrolysis in 0.3 M HCl was found to be a maximum when the sodium chloride concentration was about 1 M. Sudden exchange experiments, in which acid was substituted for sodium chloride after various times of hydrolysis, revealed a successive shortening of the extractable fragments during the low acid concentration hydrolysis. The results strengthen the view that, during hydrolysis, apurinic acid is lost from the cells through a reaction whose form is determined, first, by an initial retardation of the depolymerization, second, by the maximum length at which fragments developed through the depolymerization become soluble and are lost by diffusion, and last, at low acid concentrations, by a mechanism whose influence is equivalent to the presence of bonds between the fragments and an unextractable stable structure.