Fig. 5.

Regulation of Nodal expression in peri-implantation embryos. a Four transcriptional enhancers—ASE, LSE, NDE, and PEE—contribute to regulation of Nodal expression. b Expression of Nodal(lacZ) BAC transgenes containing all enhancers or lacking either ASE alone, ASE and LSE, or ASE, LSE, and PEE was determined in embryos at E4.5 and E8.2 by X-gal staining. Scale bars, 50 μm. In E4.5 embryos, the relative levels of Nodal expression in the different embryos are indicated by plus signs. Frontal and lateral views are shown for E8.2 embryos. X-gal⁺ regions are schematically summarized in diagrams on the right. Note that ASE and LSE are active in the lateral plate mesoderm, whereas NDE is active in the node⁴⁰. c E3.2 embryos harboring a Nodal(Tomato) BAC transgene were cultured for 24 h with 10 µM SB431542 or dimethyl sulfoxide (DMSO) vehicle and were then examined for Tomato and GATA6 immunofluorescence. d Expression of the Nodal(lacZ) BAC transgene in Foxh1 ^+/+ and Foxh1 ^–/– embryos at E4.5. Scale bars, 50 µm. e Regulatory relation between Nodal and Lefty at the peri-implantation stage. The genes constitute a SELI system, as they do for L–R patterning at E8.0