The Feulgen reaction at the electron microscopy level

Abstract

The Feulgen reaction has been the first specific method for detecting DNA available at light microscopy since 1924. However, a similar specific method was proposed for electron microscopy only 50 years later. Here, we discuss the problems encountered in finding the electrondense reagent capable of taking advantage of the extremely high resolution offered by electron microscopy as well as some applications of the method.

Figure 1.

Reproduction of a protocol, signed by Roland Cogliati, reporting a modification in the synthetic procedure of osmium ammine, posterior to the original published paper. The reagent is named New POS (POS stands for Préparation d’Osmium – in French).

Figure 2.

OA staining of a P815 cell nucleus. a) Only DNA is stained, the contrast in the cytoplasm is due to acrylate embedding; note the nucleoli (nc) which appear clearer than the surrounding nucleoplasm; scale bar: 2.5 µm. b) High magnification of the nucleolar chromatin; dfc, dense fibrillar component; asterisk, fibrillar centre; arrow, thin fibres of DNA; scale bar: 500 nm. c) In the inner part of the nucleolus, fibrils of naked DNA (arrowhead) as well as in the nucleosomal configuration (arrow) are present; scale bar: 100 nm.