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Fig. 2. RNA injection of Six6, Six3 or Xsix3 at high concentrations leads to retinal expansion by midbrain transformation. Whole-mount in situ hybridization of neural groove stage embryos (stage 18; anterior view). (A,E,I,M) Non-injected control embryos. (B,F,J,N,Q,R) Six6 injected embryos. (C,G,K,O,S) Six3 injected embryos. (D,H,L,P) Xsix3 injected embryos. The injected side is always on the right (except for Q). (B–D) Ectopic expression of Xpax2 in the optic area extends into the presumptive midbrain territory (red arrowhead). Expression at the midbrain/hindbrain boundary is lost (black arrowhead). (F–H) Enlarged Xpax6 expression domain in the eye primordia and ectopic expression in the presumptive midbrain area (red arrowhead). The forebrain/midbrain boundary (black arrowhead) normally demarcated by Xpax6 is lost. (J–L) Expanded Xrx expression in the optic area and ectopic expression in the presumptive midbrain territory (red arrowhead). Normal limit of Xrx posterior expression domain (black arrowhead). (N–P) Xen2 expression at the midbrain/hindbrain boundary is absent (red arrowhead), while Xkrox20 expression in the hindbrain rhombomeres 3 and 5 is maintained. Normal Xen2 expression domain at the midbrain/hindbrain boundary (black arrowhead). (Q) Six6 injected mRNA is still present in the injected side of the embryos at the neurula stage, as visualized with an antisense Six6 riboprobe (arrowhead). (R) Xsix3 expression domain (black arrowhead) remains limited to the optic area upon Six6 injections (red arrowhead). (S) Moderate expansion of Xsix3 expression domain into the midbrain area upon Six3 injections (red arrowhead). |
