Fig. 1

Dorsal neural tube restriction of zic1 and zic4 linked genes during embryonic development. (A, B) Dorsal view (anterior to the top) of RNA in situ hybridization of zic1 (A) and zic4 (B) at their onset of expression at 75% epiboly (zic1) and 90% epiboly (zic4) in the anterior (asterisks) and lateral border (arrows) of the neural plate. (C–M) Developmental stages are as indicated; dorsal (C, D, G–L) and lateral (E, F, M) views, anterior to the left. Transverse sections of the neural tube (outlined with yellow dots) (G′, I′, K′). (C–F) Whole-mount embryos showing modulated zic1 (C, E) and zic4 (D, F) expression along the AP axis (C, D) and dorsal restriction of expression in the neural tube (E, F). (C–F) krox20 is a marker for r3 and r5. (G–I) zic4 RNA in situ hybridization of whole-mount embryos highlighting the progression of hindbrain ventricle opening (arrows) from 18.5 hpf (G) to 21 hpf (H) and 24 hpf (I). Note dorsal restriction of zic4 expression in transverse sections through r5 at 18.5 hpf (G′) and 24 hpf (I′), as indicated by white dotted lines in panels G and I respectively. Note at 18.5 hpf (G′) the absence of a ventricle opening, while at 24 hpf (I′) the opening is clearly defined. zic4 is expressed in the roof plate (RP) indicated by arrow in panel I′. (J–M) zic1 (J) and zic4 (K–M) transcripts continue to be expressed in the dorsal neural tube. Arrow in panels J and K indicates the expression of zic1 and zic4 respectively in an unidentified population of dorsal midbrain neurons. Dorso-lateral expression domain of zic4 is maintained at 48 hpf (K′) in transverse section at level indicated by white dotted line in panel K. t, telencephalon; d, diencephalon; m, midbrain; h, hindbrain, s, somites.