Embryonic lethality is not sufficient to explain hourglass-like conservation of vertebrate embryos

Uchida, Y., Uesaka, M., Yamamoto, T., Takeda, H., Irie, N.
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Pharyngula stages did not show the highest rate of lethal phenotypes following transient perturbations. a Representative embryos that showed malformation or lethal phenotype. (I–IV) Zebrafish embryos with (I) curled trunk, (II) bent trunk axis, (III) pericardial edema, and (IV) shortened trunk. (V–VIII) African clawed frog embryos with (V) curled trunk and small eyes, (VI) severely bent trunk, (VII) edema and abnormal head, and (VIII) bent trunk axis. (IX, X) Chicken embryos with (IX) abnormal head and growth arrest, and (X) small eyes. Scale bars represent 1 mm (I–VIII) and 5 mm (IX, X). bd Rate of lethal phenotypes rate after transient perturbation in b zebrafish, c African clawed frog, and d chicken. Phenotype evaluation was performed at hatch period in zebrafish, st. 45 in African clawed frog, and HH25 in chicken. Blst blastula, Gst gastrula, Pha pharyngula, Lat late embryo, ctrl untreated control group. Data are displayed as means, and error bars denote SD. Only significant differences between each treated group and the control group are shown. *P < 0.05, **P < 0.01, ***P < 0.001 (Tukey–Kramer method)

Developmental dynamics of zebrafish embryos showing normal development and examples of embryonic death. After UV irradiation, embryonic survival was tracked by time-lapse imaging in 1-h intervals until the hatch period (at least 60 h). The elapsed time from the start of recording is indicated in the upper left corner in each panel. (a) Entire time-lapse sequences of the typical normal development of a zebrafish embryo. (b, c) Examples of embryonic death; in these cases, we determined that embryonic death occurred at 6 h (b) and 19 h (c), respectively. In both frames, critical deformation and cessation of development were observed.

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