Figure 4.

Active cycling in the mitotic region. (A–C) Single confocal sections of germ lines extruded after BrdU pulses of increasing times. Pink, anti-BrdU; blue, TO-PRO-3 DNA dye; dashed line, mitotic region/transition zone boundary, arrowheads, distal end. (A) 15-min BrdU pulse. BrdU labels nuclei in both mitotic region left of dashed line and transition zone to its right. Nuclei with crescent-shaped DAPI staining are BrdU-negative and are likely to be in meiotic prophase; nuclei whose DAPI staining appears round are BrdU-positive and are likely to be in premeiotic S-phase (white arrowheads). (B) 4-h BrdU pulse. (C) 8-h BrdU pulse. All mitotic germ cells contain some BrdU label. Inset, boxed region. Lightly labeled germ cell in box (white arrowhead) is shown in a different focal plane in inset (white arrowhead). (D) Percent BrdU-positive nuclei in the high mitotic index region at increasing times of BrdU treatment. Each circle represents one germ line; red filled circles represent germ lines in which all germ cells show some BrdU labeling. Red lines indicate mean. This data represents all except the proximal 4 rows of the mitotic region; more proximal rows frequently contained several unlabeled nuclei even after 12 h, but most (>95%) were labeled. (E) Percent BrdU-positive nuclei at different positions along the distal-proximal axis. Each line represents data from all nuclei in a 2-row interval along the distal-proximal axis. Time course for complete incorporation is similar at these positions.