Fig. 1

Standard Heat Shock causes a cell cleavage stall at the first cell cycle, and HS2 a stall at the second cell cycle. A–C: Control untreated embryos at the indicated time points, corresponding to the two-, four-, and eight-cell stage. D–F: An embryo with a one cell cycle stall during the first cell division, caused by a heat pulse initiated at 13 mpf (standard Heat Shock (HS)). G–I: An embryo with a one cell cycle stall during the second cell division, caused by a heat pulse initiated at 22 mpf (HS2). Embryos exhibiting a cell cycle stall resume cleavage after the stall and contain half the number of blastomeres as control stage-matched embryos. J: Comparison of the degree and type of cell cycle stall caused by standard Heat Shock and HS2. Standard Heat Shock causes primarily a stall of the first cell division, whereas HS2 primarily causes a stall of the second cell division. Values are mean percentages across four different trials.