Fig. 4

Electron microscopy analysis of the notochordal basement membrane from 30 hpf scarb2a mutants. All images shown are transverse cross-sections close to somite 16 of 30 dpf zebrafish embryos. In this figure, images were arranged so the outer layer of the basal membrane was oriented toward the top or top-left corner regardless of the embryo orientation. The dorso–ventral axis of the larvae is indicated by a double arrow. A,C: WT zebrafish embryos prepared for electron microscopy. B,D: Mutant embryos scarb2a^hi1463Tg also prepared for electron microscopy. A,B: Images of the basal membrane at the dorsal side of the notochord. C,D: Images of the basal membrane at the ventral side of the notochord. All mutant embryos were genotyped first to ensure that they were scarb2a^hi1463Tg homozygous embryos (see Experimental procedures). All images are shown at 5,000X magnification. Square brackets to the sides of each figure indicate basal membrane thickness, which was wider in the mutants (see asterisks). The insets show higher magnifications (10,000X) of selected regions (dotted boxes). Arrowheads point to electron-dense particles observed in the medial basal membrane in scarb2a^hi1463Tg homozygous embryos, and dotted arrows point to thickened inner basal lamina in mutant embryos. Outer basal membrane (O), medial basal membrane (M) and inner basal membrane (I). Scale bars = 500 nm.