Subdivision of the mitotic cycle into eleven stages, on the basis of the chromosomal changes observed in mouse duodenal crypt cells stained by the DNA-specific Feulgen reaction.

The Feulgen reaction has been utilized to localize DNA in nuclei throughout the cycle of mouse duodenal crypt cells using Epon-embedded 1 micron thick sections. The observed changes indicate that the 12.3 h long mitotic cycle of these cells can be subdivided into eleven stages, seven of which take place during the interphase. Computer measurements of Feulgen-stained nuclei and previous radioautographic studies indicate that DNA synthesis begins during stage I and ends during stage IV. The staining pattern shows no distinctive feature in the nuclei of the 1.5 h long stage I. Thereafter, marked changes occur during the rest of the interphase--that is during the 6.3 h that precede karyokinesis and the 3.5 h that follow it. Thus, at stage II the background of the nuclei darkens; at stage III, there appear stained threads interpreted as densifying chromosomes and dots interpreted as chromomeres, both of which thicken from 0.2 to 0.4 micron; at stage IV they further thicken to about 0.5 micron and at stage V, to about 0.7 micron. At this stage, which approximately corresponds to prophase, the intensely stained, discrete dots are localized within the less intensely stained sausage-shaped threads. As the breakup of the nuclear envelope introduces stage VI, whose early part corresponds to prometaphase, the intensely stained dots become close to one another within the threads and eventually fuse. The staining of the threads thus intensifies, and, by the late part of the stage that corresponds to metaphase, they have become the homogeneously dense metaphase chromosomes. At stage VII, the anaphase chromosomes reach each pole where they associate into a compact mass.(ABSTRACT TRUNCATED AT 250 WORDS)