|10% Buffered Formalin (Sigma, HT50-1)
||Cross-link proteins and nucleic acids and has a mode of action very different from acetone and ethanol. Formalin fixation appears to create a migration barrier that, under certain specified conditions, severely limits the movement of the PCR product from its site of synthesis in the cell. It is reasonable to assume that this relates to the protein-DNA latticework that occurs secondary to the cross-links created after formalin fixation.
|Acetone and Ethanol
||Denature proteins and, in this way, render degradative enzymes inoperative. Ethanol and acetone fixation allow intranuclear DNA synthesis, but that, in many cells, the PCR product migrates out of the cell.
|10% Buffered Formalin (Sigma, HT50-1) with Picric acid (e.g., Bouin's solution) or with a Heavy Metal such as Mercury (e.g., Zenker's solution)
||Give better nuclear detail with microscopic sections (bone marrow and lymph node biopsies). However, fixatives that include a heavy metal or picric acid do not allow PCR because of the rapid and extensive degradation of the DNA. Tissues fixed for more than 8 hours in solutions that contain either a heavy metal or picric acid do not permit a signal with in situ hybridization, although shorter-term fixation can yield intense signals.
|Frozen, Unfixed Tissues
||For preservation of the antigens determinant