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Figure 3. IGF Signaling and the Head/Trunk Boundary(A) Uninjected 3 day tadpole in lateral view.(B) Embryo injected with 500 pg of DN-IGFR mRNA per animal blastomere at the 4- to 8-cell stage showing reduction of cement gland and eye structures (92%, n = 48).(C–H) The domains of expression of Otx-2 (head), XAG-1 (cement gland), and Rx2a (eye) markers are reduced by DN-IGFR mRNA.(I–N) Dorsal views of neurula stage embryos injected into one blastomere at the 4-cell stage with nuclear lacZ mRNA (note red nuclei). In situ hybridization was performed at neurula stage with probes for Six-3 (I–K) or a combination of Otx-2 and the trunk marker HoxD1 (L–N). IGF-2 (400 pg) shifts the head/trunk border caudally (n = 25) and DN-IGFR mRNA (500 pg) displaces it anteriorly (n = 15). IGF-2 and DN-IGFR mRNA injections do not significantly change the number of nuclear LacZ-labeled nuclei |
