BMP4 expression overlaps with intracellular BMP inhibitor expression and intermediate Smad1/5/8 activation.

<p>(A) HCR shows expression of <i>bmp4</i>, <i>ckip-1</i>, and <i>smurf1</i> in wild-type HH6 chick embryos. (B) Immunostaining for the NPB marker Pax7 and phosphorylated Smad1/5/8 in HH6 embryos. (C) Line traces of <i>bmp4</i>, <i>ckip-1</i>, and <i>smurf1</i> expression compared with Pax7 and pSmad1/5/8 staining intensity from the boxed regions in A-B show high <i>bmp4</i> expression and intermediate pSmad1/5/8 staining in the Pax7+ NPB domain. Underlying data can be found in <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.2004425#pbio.2004425.s006" target="_blank">S1 Data</a>. Scale bars represent 200 μm. BMP, bone morphogenetic protein; CKIP-1, casein kinase interacting protein 1; HCR, hybridization chain reaction; HH6, Hamburger-Hamilton stage 6; NNE, nonneural ectoderm; NP, neural plate; NPB, neural plate border; Pax7, paired box 7; pSmad1/5/8, phospho-Smads 1/5/8; Smurf1, Smad ubiquitin regulatory factor 1.