Fig. 6. Expression patterns of Smad1, Smad5 and Smad8. Brightfield and darkfield images of sagittally sectioned embryos at 6.5 (A,D,G), 7.25 (B,E,H) and 8.5 dpc (C,F,I) hybridized using Smad1 (A-C), Smad5 (D-F) or Smad8 (G-I) specific probes. (A,A') At the onset of gastrulation, Smad1 is highly expressed in the VE and early primitive streak. (B,B') At late streak stage, Smad1 is observed in the VE, extra-embryonic and embryonic mesoderm derivatives. as well as the primitive streak. (C,C') By 8.5 dpc, Smad1 is ubiquitously expressed. (D,D') At 6.5 dpc Smad5 is uniformly expressed at low levels throughout the conceptus. (E,E') At late streak stages, Smad5 is expressed throughout the embryonic region and the allantois. (F,F') Smad5 transcripts are found throughout 8.5 dpc embryos. (G,G') At 6.5 dpc a Smad8 hybridization signal cannot be discerned from background. (H,H') At late primitive streak stages, Smad8 is expressed in the VE, posterior primitive streak and extra-embryonic mesoderm derivatives. (I,I') By 8.5 dpc Smad8 is widely expressed. al, allantois; am, amnion; ch, chorion; ec, ectoderm; ep, epiblast; ps, primitive streak; ve, visceral endoderm.