Alteration of N-CoR expression resulting in changes of hindbrain length between r6 and s1 similar to those changes caused by altering RA signaling in zebrafish embryos at 11-somites stage. Embryos at 1- to 2-cell stages are microinjected with N-CoR mRNA (C and D) or n-cor MO (I and J) to enhance or impair zebrafish N-CoR function, respectively. Alterations of RA signaling in embryos are performed by exogenous administration of 1 μM DEAB (E and F) or 10 nM RA (K and L) to reduce or enhance RA signaling, respectively. All treated embryos (C–F and I–L) together with wild-type control embryos (A and B) and control MO microinjected embryos (G and H) are grown to 11-somite stage and then hybridized by RNA probes of val (marking r5 and r6) and myoD (marking s1). Whole mounted embryos (A, C, E, G, I and K) are positioned anterior left and viewed laterally whereas flat-mounted embryos (B, D, F, H, J and L) are positioned anterior left and viewed dorsally. The lengths between r6 and s1 of the embryos overexpressing N-CoR (D) or treated with DEAB (F) are shorter than those of control embryos (B). The control MO microinjected embryo (H) has similar length between r6 and s1 to control embryos (B). The lengths between r6 and s1 of the n-cor knocked down (J) or RA treated embryos (L) are longer than those of the control embryos (B and H). r, rhombmere; s1, the first somite.
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