- Feulgen stain
Feulgen stain is a
stainingtechnique discovered by Robert Feulgenand used in histologyto identify chromosomal material or DNAin cell specimens. It depends on acid hydrolysisof DNA, therefore fixating agents using strong acids should be avoided.
The specimen is subjected to warm (60 °C)
hydrochloric acid, then to Schiff reagent. In the past, a sulfite rinse followed, but this is now considered unnecessary. Optionally, the sample can be counterstained with Light Green SF yellowish. Finally, it is dehydrated with ethanol, cleared with xylene, and mounted in a resinous medium. DNAshould be stained red. The background, if counterstained, is green.
The Feulgen reaction is a semi-quantitative technique. If the only aldehydes remaining in the cell are those produced from the
hydrolysisof DNA, then the technique is quantitative for DNA. It is possible to use an instrument known as a microdensitometeror microspectrophotometerto actually measure the intensity of the pink Feulgen reaction for a given organelle. Using this procedure, it was early determined that interphase cells were composed of two populations, those with diploid DNAand those with tetraploid DNA(two complete genomes). The nuclei looked identical, but one contained twice as much DNA. This gave rise to the division of the interphase period of the cell cycleto G1, S, and G2 phases based on the synthesis of that extra DNA. [http://homepages.gac.edu/~cellab/chpts/chpt2/ex2-5.html]
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