Fig. 5

Cyclin B1 mutants have an abnormal cell cycle progression. (A-A″) anti-pH3 staining shows spr mutants have fewer cells in mitosis between the egr2b stripes in rhombomeres 3 and 5, dorsal view. Mitotic cells align at the dorsal midline (white arrow) in the wild-type embryo (A), but do not in the spr^tu21 mutant (A′) whose mitotic cells are irregularly shaped. In the spr^ro1 mutant (A″), pH3 staining is weak and reveals few mitotic cells. (B) Quantification of the number of mitotic cells between the egr2b stripes in the wild-type embryos (grey), spr^tu21mutant (yellow), and spr^ro1 mutant (green) between 7- and 25-somites (12 h and 21.5 h). Starting at 15-somites (16.5 h), the number of mitotic cells in the spr^tu21 allele is significantly fewer (p < 0.05) compared to wild-type embryos. The counts for the spr^ro1 allele are statistically significant compared to both, wild-type and spr^tu21 at all stages (p < 0.01). (C-E″) The Dual FUCCI transgene shows that cells in the sprmutant reside in the wrong phase of the cell cycle at 20-somites. Shown are populations of cells in the tail where the cell cycle reporter mCherry-Cdt1 (red) defines cells in G1 (G0) stage (C–E) and the Cerulean-Geminin (blue) defines cells in S/G2/early M stages (C′-D″). Whereas the majority of cells in wild-type embryos are in the G1 (G0) stage of cell cycle (C-C″), the majority of cells in spr^tu21 (D-D″) and spr^tu21/ro1 (E-E″) mutants are in the S/G2/early M phase of the cell cycle. Scale bar is 100 μm. Inserts show that G1 (G0) cells have abnormal shapes in mutant embryos, scale bar is 10 μm.