Fig. 4

Periderm proliferation decreases as the axial elongation rate slows. (A) Schematic of the Cdk2 sensor. The fluorescently tagged protein shuttles in and out of the nucleus. Based on the cytoplasm-to-nuclei signal ratio, we determine the cell cycle status. (B) Maximum projection view of representative embryos expressing krt4:Cdk2-KTR-mCherry, (Scale bar, 100 µm.) Higher-magnification view of cells in the boxed region of (A) tracked through time shows translocation of the sensor as cells transition from G2/M to G1 postmitosis. (Scale bar, 10 µm.) (C) Quantification of Cdk activity in periderm cells classified as mitotic or nonmitotic based on their ability to divide during the imaging. Expectedly mitotic cells have much higher Cdk activity compared to nonmitotic cells. (D) Maximum projection view of embryos expressing krt4:Cdk2-KTR-mCherry at 29 hpf and 54 hpf. The sensor predominantly shifts to the nucleus in later stages, indicating G1 phase entry. (Scale bar, 100 µm.) (E) Quantification of the percentage of mitotic cells at 28 to 30 hpf and 52 to 54 hpf shows significant reduction in the number of cells in G2/M at the latter stage. Average percentage of mitotic cells at 28 to 30 hpf – 44.23%, n = 9 embryos; at 52 to 54 hpf – 4.72%, n = 7 embryos. Welch’s t test P <0.0001