THE STUDY OF THE CELL-NUCLEUS USING CRYOFIXATION AND CRYOSUBSTITUTION

New pathways leading to a better understanding of the cell nucleus mor pho-functional aspects are being opened up by cryofixation and cryosub stitution methods. These techniques are able to produce excellent morp hology of the nuclear fine structure with subtle, sometimes even notab le, ultrastructural differences when compared with conventional chemic ally fixed, dehydrated and embedded material. It is of particular inte rest, when carrying out these cryotechniques, to avoid the use of any cryoprotectant and chemical fixation. This permits an analysis of the cell's fine structure, which may well approach its native state. Cryof ixation, because of its extreme rapidity, should be able to immobilize all cell activities and capture a well defined physiological state of the cell without causing major changes in molecular structures. Immun ocytochemical studies carried out using cryofixation and cryosubstitut ion, gave very satisfactory results, often revealing antigenic sites w hich were not, or hardly ever, detected when using conventional fixati on techniques. The applications of various cryofixation and cryosubsti tution methods in the study of the cell nucleus are summarized and an attempt to critically evaluate their results is made in this review.