Fig. 6. Immunohistochemistry for BrdU in an embryo at the late four-cell stage fertilized with cultured sperm. (A) Whole-mount immunohistochemistry. Two positives in each cell indicate chromosome division (arrowheads). (B) Section immunohistochemistry: BrdU-positive cells indicate that chromosomes have already divided (arrowheads). The remaining positives were found in other sections (not shown). (C) Control of whole-mount immunohistochemistry subjected to BrdU detection. (D,E) Control of section immunohistochemistry subjected to BrdU detection (D) and to Hematoxylin staining (E). Scale bars: 50 µm in A for A and C and B for B,D,E.