DNA Ploidy

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Ploidy is a cytogenetic term used to describe the number of chromosome sets, or deviation from the normal number of chromosomes in a cell. In cytometry, the expression DNA ploidy is used either to describe the DNA content in a cell or the total DNA distribution in a cell population.

DNA Ploidy process

Overview

We have developed an image analysis system for DNA ploidy analyses based on the Feulgen technique, which is a widely used staining method in biology. The Schiff or Shiff-related reagent is used to bind to aldehyde groups which are yielded after hydrolysis with HCl. This allows for DNA staining in situ. The color intensity is proportional to the DNA concentration and the amount of DNA in the nucleus is an expression of light absorbed by the Feulgen stain in the entire nucleus. The Feulgen reaction is used to quantify the DNA ploidy distribution in tumor nuclei.

The picture of the nuclei is transferred from a microscope to a computer, via a high resolution digital camera. The computer measures the absorbed amount of light, which provides an expression of the amount of DNA in each nucleus:

Scanning

Prognostic markers

Automatic classification of cell types

A condition for automatic DNA ploidy analysis is that one must classify nuclei in relation to the cell type it was isolated from (epithelial nuclei or nuclei from connective tissue, as well as lymphocytes and plasma cells from the tumorís blood supply). With the system we use today 70-80 % of the nuclei are classified correctly. The rest must be edited manually. As we measure between 1000-15000 nuclei per specimen, this is acceptable. A drastic benefit with a system based on scanner technology, is that one can relatively quickly measure all of the nuclei in the specimen (>10,000). The manual editing job will however be then too time-consuming in this case, and we must therefore develop a better classification algorithm and increase the correct classification rate to between 90-95 %. We hope to be finished with this by September 2008.

Automatic classification of DNA histograms

DNA histograms are today classified manually. As the last phase in automization, we would like to develop an algorithm for automatic classification of such histograms. We are planning on finishing this by September 2008.