Fig. 4. The activity of both Him and Her5 is necessary to prevent neurogenesis across the medial IZ in vivo. (A-D) The inhibition of either Him or Her5 function triggers ectopic neurogenesis in place of the MIZ (dorsal views of the MH region in flat-mounted embryos at the four-somite stage, anterior to the left). Embryos are probed for ngn1 (blue) and pax2.1 (red) expression following injection of her5MO^ATG(A), himGripNA^ATG (B), himGripNA^SPL (C) (orange labels), compared to a non-injected WT control embryo (D). Note that the vcc and r2MN are bridged by ectopic ngn1-positive cells (double arrows) after blocking Her5 or Him activity, while other undifferentiated areas are not affected (e.g. area between r2MN and r4MN, asterisk. (G-L) him and her5 expression are not successive and interdependent steps of the anti-neurogenic cascade acting in the MIZ (dorsal views of the MH area in flat-mounted embryos at the three-somite stage, anterior to the left, used markers are color-coded). (G,H) him expression in wild-type embryos (H) or after injection with her5MO^ATG (G). Note that him expression is not modified. (I-L) Expression of her5 (I,K) and GFP (J,L) in her5PAC::egfp embryos injected (K,L) or not (I,J) with himGripNA^ATG. Note that her5 and GFP expression are unaffected. vcc: ventro-caudal cluster, r2MN: prospective motorneurons of rhombomere 2, r4MN: prospective motorneurons of rhombomere 4.