||Fig. 1 (Left). Expression of purine nucleoside phosphorylase. (A)
Vegetal view of an early gastrula (stage 10.5), with a strong expression in the dorsal marginal zone. (B) Vegetal view of a stage 11 gastrula. The transcripts are detected in the entire marginal zone. (C) Section from the line in (B), showing expression in the deep layer of dorsal marginal zone cells. (D) Dorsal view of a stage 15 early neurula. Expression is localized to the posterior region and the entire neural plate. (E) Section from the line in (D), showing expression in the deep layer of neural plate and absence of expression in the somites and notochord. (F) Lateral view of a stage 22 early tail-bud embryo, with the expression essentially de- tected in the tail bud and the forming otic vesicle (OV). (G) Section from inset in (F), showing expression in deep cells of the tail bud. (H) Lateral view of a stage 28 tail-bud embryo. The expression is restricted in the posterior tip of the tail bud and in the otic vesicle (OV). (I) Section from inset in (H), with higher magnification of the otic vesicle. (J) Section corresponding to inset in (H), showing expression in the tail bud including both unsegmented posterior mesoderm and neural precursor cells.