Fig. 4

Fig. 4 Repression of posterior neural fates by the dominant interfering mdk2 variant mdk^Δ38. (A to D) Coexpression of mdk^Δ38 rescues head deficiencies induced by ectopic mdk2 expression. (A) Embryos exhibiting a strong posteriorized phenotype at 48 h after injection with 110 pg mdk2 and 330 pg prolactin RNAs. Note that ectopic mdk2 leads to specific repression of head and eye structures and to some curved tails. (B) Partial rescue of head deficiencies by co-injection of 110 pg mdk2, 220 pg mk^Δ38, and 110 pg prolactin RNAs. (C) Greater rescue of head deficiencies by co-injection of 110 pg mdk2 and 330 pg mk^Δ38. The majority of head structures appear indistinguishable from those of uninjected control embryos (D). The posterior defects observed are likely due to mdk^Δ38 interfering with endogenous mdk2 function. (E, F) 24-h embryos injected with 200 pg wild-type mdk2 (E) and mdk^Δ38 (F). Note anterior truncation resulting from gain of function (E, arrowheads) and posterior deficiencies resulting from loss of function (F, arrowheads). (G) Lateral view of gsc expression in an uninjected embryo at 80% epiboly. (H) gsc expression (arrow) is unaffected in mdk^Δ38-injected embryos. (I–O) 12-h embryos, dorsal view, anterior to the top. (I) pax2 (arrowhead) and krox20 (arrows) expression in an uninjected embryo. (J) Repression of krox20 expression in rhombomeres 3 and 5 of an embryo unilaterally injected with mdk^Δ38. Expression of pax2 at MHB appears normal compared to I. (K) fkd6 staining (red) in an uninjected embryo. (L) Expansion of the fkd6-positive neural crest domain in mdk2-injected embryo. (M) Repression of fkd6 by mdk^Δ38 in one half of a unilaterally injected embryo (arrow). (N–R) Ectopic mdk^Δ38 expression blocks formation of posterior moto- and sensory neurons. (N) isl1 expression in Rohon–Beard sensory neurons (rb) and motoneurons (mn) of an uninjected embryo at 12 hpf. (O) Unilateral lack of both neural fates in an embryo unilaterally injected with mdk^Δ38. (P–R) Dorsal view of 10-h embryos. (P) isl1 expression in an uninjected embryo. (Q) Primary neurons appear unaffected in a mdk2-injected embryo. (R) Note unilateral absence of sensory neurons (arrowhead) in mdk^Δ38-injected embryo.