Labeling the nucleus with fluorescent dyes for imaging.

INTRODUCTIONThe eukaryotic cell has evolved to compartmentalize its functions and transport various metabolites among cellular compartments. Therefore, in cell biology, the study of organization and structure/function relationships is of great importance. The nucleus contains almost all of the cell's DNA and is bounded by a double membrane. Inside and adjacent to the inner membrane of the nuclear envelope is the nuclear lamina. It is composed of a fibrous meshwork comprising one or more of three major intermediate filament-like polypeptides: lamins A, B, and C. The outer nuclear membrane is contiguous with the endoplasmic reticulum. Several fluorescent stains are available that label DNA and allow easy visualization of the nucleus in interphase cells and chromosomes in mitotic cells. These stains include Hoechst and 4',6-diamidino-2-phenylindole (DAPI), which are used in this article. Although not as bright as the vital Hoechst stains for DNA, DAPI has greater photostability. One advantage of Hoechst 33342 over DAPI is that the former is membrane-permeant and is, therefore, useful for imaging living cells, because it does not require cell fixation or permeabilization.