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. 1999 Sep 28;96(20):11376–11381. doi: 10.1073/pnas.96.20.11376

Figure 2.

Figure 2

Shh controls Lefty-1 expression. All embryos are viewed from the ventral side (left side of the embryo corresponds to the reader’s right). Phenotypes or experimental manipulations, followed by the probe used for in situ, are shown at the bottom of each panel, unless otherwise indicated. (A-H) Expression of Lefty-1, Lefty-2, Nodal, and Pitx2 in E8–8.5 Shh−/− embryos. (A and B) Lefty-1 normally is expressed on the left side of the presumptive floor plate (arrowhead in A) and weakly on the left LPM (arrow in A). In Shh−/− mice (B), expression of Lefty-1 is not detected, neither in the midline (arrowhead) nor the left LPM (arrow). (C and D) Lefty-2 also is expressed in the midline (arrowhead) and more strongly on the left LPM (arrow) of wild-type embryos (C). In Shh−/− embryos, Lefty-2 expression in the midline is not detected (white arrowhead), whereas an ectopic induction on the right LPM (red arrow) is observed (D; black arrow shows normal expression in the left LPM). (E and F) Nodal, normally expressed on the left LPM (arrow in E), is ectopically induced on the right LPM of Shh−/− embryos (red arrow in F). (G and H) Similarly, Pitx2, normally expressed on the left LPM (arrow in G) is ectopically induced on the right LPM in Shh−/− embryos (red arrow in H). (I-J) In the mouse, Shh is expressed symmetrically in the head process at E7.5-E8.5 (I). Lefty-1 transcripts are localized on the left side of the perspective floor plate (J). (K and L) In the chick, asymmetric expression of Shh on the left side of the node at stage 5+ coincides with the initial asymmetric expression of Lefty-1. (M and N) In subsequent stages (7 to 9), Lefty-1 and Shh transcripts overlap in a symmetrical pattern in the notochord of the chicken embryo. (O-Q) Shh beads implanted on the right side of the chicken node at stage 6 induce an ectopic patch of Lefty-1 expression that is observed on the posterior right LPM (red arrow in O; black arrow shows normal expression in the posterior left LPM). When beads soaked in a blocking anti-Shh antibody are implanted on the left side of a stage 6 chicken embryo, Lefty-1 expression is neither detected in the midline nor in the posterior left LPM (Q, compare with the normal pattern in P). WT, wild type.