Fig. 3. E2f1 protein accumulation during embryogenesis. w¹¹¹⁸ embryos were pulse-labeled with BrdU for 5 minutes and stained for E2f1 (green), BrdU incorporation (red) and phospho-tyrosine (cyan). Embryos undergoing (A) S₁₃; (B) S₁₄; and (C) G2₁₄. (D) S₁₅ cells are indicated by arrows in the BrdU image; the remainder are still in G2₁₄. Note that entry into M₁₄ is not synchronous throughout the embryo, resulting in groups of cells called mitotic domains that proceed through the cycle coordinately and that generate a reproducible and stereotypic pattern of BrdU incorporation [e.g. the top arrow indicates mitotic domain 11 (Foe, 1989)]. (E) Cycle 15 in the ventral epidermis (bracket) and S₁₆ in the dorsal epidermis (bar). (F) S₁₆ in the ventral epidermis (bracket) and G2₁₆-G1₁₇ in the dorsal epidermis (bar). Arrowheads in E-H indicate amnioserosa cells. (G,H) Although most cells of the epidermis have entered G1₁₇ (see Fig. 2C), some cells continue into cycle 17 (arrows in the BrdU image). (I) G1₁₇. Scale bar: 50 µm.