Blocking Nodal function prevents expression of ventral and dorsal marker genes in the presumptive ectoderm and causes massive ectopic expression of ciliary band genes.
(A) morphology of nodal morphants at 72h. Note that most of the ectoderm of these embryos differentiates into a thick ciliated ectoderm that resembles the ciliary band ectoderm. (B–D) Embryos were injected with a Nodal morpholino or treated with the Nodal receptor inhibitor SB431542 and the expression of ventral, dorsal or ciliary band genes was analyzed at the relevant stages. (B,C) All the ventral and all the dorsal marker genes tested required Nodal to be expressed in the presumptive ventral and presumptive dorsal ectoderm respectively. However, in the nodal morphants, a number of genes expressed dorsally continued to be expressed in the ectoderm derived from the vegetal region and/or in the mesendoderm including tbx2/3, id, irxA, nk2.2, atbf1, admp2 and 29D (the residual expression of tbx2/3 is not visible here since it is mostly visible at gastrula stages). This indicates that in the nodal morphants there is a residual D/V polarity with the vegetal most ectoderm adopting a dorsal identity. (D) Inhibition of Nodal signaling caused a massive ectopic expression of ciliary band genes throughout the ectoderm. Note that genes expressed throughout the ciliary band territory such as bmp1, otx, onecut, gfi1, dri, or tubulinß3 are ectopically expressed throughout the ectoderm of Nodal morphants. Genes that are expressed in sub domains of the ciliary band such as pax2/5/8, fgfA, univin or wnt8 are also ectopically expressed and display a radial expression but in accordance with their normal animal-vegetal boundaries. The neural marker Delta and the ciliary band antigen 295, which in control embryos labels the ciliated cuboidal cells of the ciliary band, are also expressed ectopically throughout the thick ciliated ectoderm typical of nodal morphants. lv, lateral view, vv, vegetal pole view, fv, frontal view. Scale bar: 100µm.