THICK-SECTION FLUORESCENCE IN-SITU HYBRIDIZATION ON FORMALIN-FIXED, PARAFFIN-EMBEDDED ARCHIVAL TISSUE PROVIDES A HISTOGENETIC PROFILE

Fluorescence in situ hybridization has become a major tool for analysi s of gene and chromosome copy number in normal and malignant tissue. T he technique has been applied widely to fresh tissue and dispersed for malin-fixed, paraffin-embedded archival tissue, but its use on section s of archival tissue has largely been limited to sections < 6 mu thick . This does not provide intact, uncut nuclei for accurate analysis of gene or chromosome copy number. We report here a method of hybridizati on to sections > 20 mu thick that overcomes these difficulties. Key de velopments were the use of DNA probes directly labeled with fluorochro mes and optical sectioning using laser-scanning confocal microscopy.