ER-xSmad6 inhibits primitive blood island development during neurulation. (A-B) Water-injected embryos cultured in the absence (A) or presence (B) of E2 develop normal ventral blood islands as assayed by benzidine staining at stage 35. (C-D) Embryos injected with 1 ng/embryo in the ventral blastomeres of 4-cell stage embryos and cultured in the absence of E2 (C) develop normal ventral blood islands. Embryos similarly injected and cultured in the presence of E2 from stage 13 (D) develop with reduced (arrow) or lacking ventral blood islands (arrowhead). (E) Northern blotting analysis using 10 μg per lane of total RNA harvested from pools of embryos injected at the 2-cell stage with 0.8 ng/embryo of ER-xSmad6 and cultured in E2 from the indicated stages (NH = no hormone). The filter was first probed with αT1-globin, then stripped and reprobed with EF-1α as a loading control. (F) Graphic representation of normalized values from panel E. Original magnification for A-D, × 20.
