Fig. 1

Axis induction defects in embryos from mothers homozygous for three different hecate mutant alleles.

A-F) Side views (except as indicated in (F)) of live embryos at 24 hpf showing a range of phenotypes from most severe (A) to normal (E) and double-axis embryos (F). A) Class V4 embryo exhibiting complete radial symmetry and lacking all anterior (e.g. head structures) or dorsalmost (e.g. notochord) structures. B) Class V3 embryo exhibiting a rudimentary axis but lacking all anterior and dorsalmost structures. C) Class V2 embryo lacking anteriormost structures such as the eyes, but showing formation of more posterior head structures such as the otic vesicles (black arrowhead, also indicated in D). D) Class V1 embryo with a relatively complete axis but reduced anterior structures, such as the eyes (white arrowhead, also labeled in E), and lacking a properly formed notochord. E) Normal embryo derived from hec mutant females indistinguishable from wild-type. Note somites in (E) are chevron-shaped, while they are blocky in (B-D) indicative of defects in notochord formation, or encircling the entire embryo in (A). F) A double-axis embryo found in hec mutant clutches exhibiting weak expressivity. Insert in the lower left shows the left axis indicated by the dashed rectangle, out of focus in the main image. Insert in the upper left panel shows a dorsal view, showing the bifurcated axis. Note the lack of defined anterior structures in both axes, as well as the lack of a notochord along the trunk, also reflected by block-shaped somites in this region. Images in A–F are side views, except for upper left insert in (F). G-I) Animal views of live wild-type embryos (G) and embryos from females homozygous for each of the three hec mutant alleles. The dorsal thickening or shield (arrow) is absent in mutant embryos. K-V) In situ hybridization analysis to detect expression of dorsally-expressed genes (gsc, chd) and ventrally-expressed genes (eve 1). The expression domains of gsc and cho is reduced in hec mutant embryos, while the expression domain of eve is expanded in these embryos. (K-V) are animal view of embryos, dorsal to the right when identifiable, at the shield stage (6 hpf). Magnification bars in (F) and (V) correspond to 100 µm for panels sets (A-F) and (G-V), respectively. Dorsal view insert in panel (F, upper left) has been reduced to 75% size.