Correlation between presence of head muscles and neural tube closure in sqt mutants. (A–E) WT and sqt embryos were raised to 3 dpf and processed in tandem for smyhc2, in the head muscles (hm) and otx5, in the pineal anlage. The adductor mandibulae (am; white arrowheads) are the first muscles to develop in the head region and were used as an indicator for head muscle presence. (A) In WT embryos, am precursors are in two clusters just anterior to the yolk sac and other jaw muscles. The pineal organ is oval indicating a closed neural tube. (B–E) sqt embryos with an (B, C) oval pineal with the am present and (D, E) divided pineal with the am present. (F) Complete set of quantitative data. All images are frontal views with anterior to the top. Scale bar: 100 µm (A–E).