Fig. 2.

Notochord excision. (A) Schematic diagram showing experimental strategy for notochordectomy. The dashed lines (a’ and a’’) show the levels of the sections shown in (Aa’) and (Aa’’). (Aa’) Transverse section through the unoperated region of an embryo fixed immediately after excision of the neural tube and notochord, and processed for shh in situ hybridization; shh expression (red) is visible in the notochord. (Aa’’) Transverse section of the same embryo through the excised region and processed for shh in situ hybridization; removal of the notochord and its sheath is confirmed, and the midline endoderm remains intact. (B) Longitudinal section of a stage 29 host embryo showing the unoperated region with notochord (posterior, downwards) and the notochordectomized region (anterior, upwards). Pax1 expression remains segmented in the grafted region anterior to the notochord (arrows), being conspicuous laterally but diminished medially in comparison with the stripes of expression seen alongside the notochord in the unoperated region. (C) Similar section to (B) in another notochordectomized embryo, showing persistent Pax1 expression both laterally and medially (arrows) in the grafted region anterior to the notochord. n, notochord. Scale bars: 100 μm.