Fig. 1. L-R asymmetric Smad1/5/8 activation and BMP antagonist expression in mouse embryo lateral plate mesoderm. (A-C) Whole-mount immunohistochemistry for phosphorylated (p-) Smad1/5/8 in 4s (A) (n=7/10) and 5s (B) (n=8/8) embryos (anterior view). Anti p-Smad1/5/8 staining in lateral plate mesoderm (LPM) is stronger on the right side than on the left (arrowhead). (C) High magnification of the boxed region from A. Rectangles demark left and right LPM. (D,E) Whole-mount lacZ staining of Bmp4^lacZ/+ embryo at 4s (n>10). Bmp4 expression is observed bilaterally at the edge of the LPM (arrowhead). Anterior (D) and posterior (E) views. The node is boxed. (F-H) Whole-mount lacZ staining of Nog^lacZ/+ embryo at 4s (F) (n=6/6) and 5s (G) (n=6/6). Nog expression in LPM is stronger on the left side than right (arrowhead). (F,G) Anterior view. (H) High magnification of the boxed region from F. (I-K) Whole-mount in situ hybridization (WMISH) for Chrd at 4s (I) (n=6/12) and 5s (J) (n=10/16). Chrd expression is stronger in left LPM than right (arrowhead). Ventral views. The dashed line indicates the extent of LPM on each side. (K) High magnification of the boxed region from I. (L) Quantitative RT-PCR results for Nog, Chrd, Bmp4 and Nodal in right versus left LPM at 4s. R, right; L, left. (M) Summary of BMP signaling activity and BMP antagonist expression at 4-5s. BMP signaling activity is represented in red (left), Nog and Chrd expression in green (right), with higher levels in a darker hue.