Fig. 11

Experimental disruption of secondary organizers in vertebrates results in a Di-Mesencephalic primordium (DiMes)-like remnant.

(A-C) A schematic representation of mouse Pax6 neural expression pattern (solid grey) in wild-type condition (WT) (A) and abolishing the function of the zona limitans intrathalamica (ZLI) (B) or isthmic organizers (IsO) (C). (B′-B′′′′) Drawings adapted from the results of Hirata et al. 2006 upon ZLI abrogation during mouse development. (C′-C′′) Immunohistochemical detection of αPax6. (C′′′-C′′′′) In situ hybridizations for Otx. (C′) and (C′′′) are WT expression domains of Pax6 and Otx, whereas (C′′) and (C′′′′) are conditional En2-Fgf8 knockout (KO) mice. (D,E) Schematic representation of pax6a gene expression (solid grey) in zebrafish embryos in WT (D) or quadruple morpholino knockdown (4MO) of otx1a, otx2, eng2a, and eng2b (E) conditions. (F) Quantification of the phenotypes observed upon 4MO treatment. All treated embryos showed a reduction in the size of the gap, even those scored as normal (indicated by an asterisk). Embryos with “reduced pax6a gap” showed only a very small expression gap, often with weak pax6a expression in it. Embryos with “no pax6a gap” had a continuous expression of the gene. (G-N) Expression patterns of key genes in WT (G-J) or 4MO (K-N) embryos. Insets in H and L showed sagittal sections of a different representative embryo. Sections of the indicated embryos. Abbreviations: Cer, cerebellum; D, diencephalon; Rh, rhombencephalon; pc, posterior commissure; pTh, prethalamus; Th, thalamus; PT, pretectum; MB, midbrain; MHB, midbrain–hindbrain boundary; T, telencephalon. Anterior is to the left. Scale bar = 100 μm.