(A) BMP4-treated embryos show ectopic expression of the midline marker
KLF1/2/4 at the tailbud stage when the treatment starts at the 110-cell stage. Embryos do not respond to BMP4 at the early neurula stage.
(B) ADMP overexpression transforms the entire tail epidermis into
KLF1/2/4-positive tissue containing
ETR-positive neurons. NOGGIN overexpression abolishes ventral midline formation.
(C) The BMP ligand ADMP is expressed in B-line midline vegetal cells (blue on scheme) underlying the ventral midline precursors (pink on scheme) at the mid-gastrula stage. ADMP MO–injected embryos do not express
KLF1/2/4 ventrally. (Lateral view, anterior to the left, dorsal to the top in all panels except in C for
admp expression pattern: anterior to the top, vegetal view (first image), sagittal section (second image and scheme)).