Fig. 2

Fig. 2 Overnight heat treatment reliably induces midline bifurcations in MZsqt embryos. (A–C) Embryonic phenotypes after overnight heat treatment. Overnight (22 h) heat treatment caused no significant defect in WT embryos (A), but led to the MB phenotype in a fraction of MZsqt embryos from every cross tested. Severe MBs extended from the trunk to the hindbrain, as demarcated by the otic vesicles (arrows) (B). Weaker MBs were limited to the trunk (C). Arrows point to otic vesicles. (D–E) Overnight heat treatment increases MB incidence in MZsqt embryos. WT and MZsqt^hi975/hi975 (D) or MZsqt^cz35/cz35 (E) embryos were cultured under standard conditions (28 °C) or heated (34 °C) overnight starting at the 64-cell stage, then scored for the MB phenotype on 1 day post fertilization. A significant difference was observed between control and heated MZsqt^hi975/hi975 embryos (p = 3.00E- 08), or control and heated MZsqt^cz35/cz35 embryos (p = 0.00126). (F) Early initiation of heat treatment is required to induce MB. MZsqt embryos pooled from several crosses were heated overnight, beginning at the indicated stages and scored for the MB phenotype on 1 day post-fertilization. Numbers of embryos scored are shown. Percentages for each phenotype are indicated: normal appearing (white); cyclopia alone (green); MB alone (red) and MB + cyclopia (yellow).