Hydrolysis in Feulgen autoradiography. I. Loss of label from S-period nuclei and its subsequent association with non-S chromatin

The Feulgen reaction: importance of the wash after hydrolysis

Washing in absolute ethanol after FEULGEN hydrolysis minimizes losses of DNA. The hydrolysis in HCl diluted in tetrahydrofuran is not superior in this respect to conventional hydrolysis if this is followed by an ethanol wash. These conclusions are based on cytophotometric and radiometric experiments made on salivary glands of sciarid larvae.

Feulgen hydrolysis at refrigerator temperature

In order to search for the better FEULGEN hydrolysis conditions, the 2 kinds of hydrolysis with 5 N HCl - at room temperature and at refrigerator temperature - were comparatively studied on rat liver imprints. 2 reactions were used: with the SCHIFF reagent binding to aldehyde groups and with methylene blue staining phosphate groups of DNA. Cytophotometry was coupled with morphological examination of stained nuclei. It was found that 1. cold hydrolysis has no substantial advantage when revealing DNA with the SCHIFF reagent but 2. it has undoubtful profit to reveal DNA, and in particular its acid-labile fraction, when staining with methylene blue. With the cold hydrolysis-methylene blue technique at least 3 categories of DNA with different acid-lability can be revealed and characterized morphologically in rat liver nuclei.

Evaluation of Feulgen reaction performed on unfixed smears

Feulgen reaction--both the original one with Schiff reagent and the modified one with toluidine- or methylene blue, pH = 4.0--can be carried out on air-dried smears without fixing. Hydrolysis--5 n HCl at room temperature should be 15 to 20 min for the original and 5 to 10 min--for the modified reaction. Binding of the dyes is stoichiometric in both cases.