Fig. 7. Localization of BMP4 to the extraembryonic region of mouse gastrulae and allantoic regenerates. BMP4 (brown color) in the extraembryonic region of mouse conceptuses in ex vivo (A,B,D,F,G) and cultured unoperated (E,H) allantoises, and allantoic regenerates (I-M). Ex vivo control conceptus [pre-binding with control peptide, CP] (C). See text for complete explanation of staining patterns. In E,H,I, embryo stages before and after culture are separated by `/'. (A) EB stage. BMP4 is present in mesoderm lining the exocoelomic cavity and in the mesothelium surrounding the allantois at this stage, as shown in this glancing sagittal section through the lateral surface of an allantoic bud, in agreement with previous results (Lawson et al., 1999). In deeper sections, the core of the early bud was negative (data not shown). (B) EHF stage. (C) EHF stage, pre-binding antibody with control peptide (+ CP). The arrow indicates faint BMP4 in yolk sac mesothelium, suggesting that this amount of control peptide (100:1, CP:anti-BMP4) was not completely efficacious in pre-binding all antibody, although all other tissues were negative. (D) Two-somite pairs (2-s). (E) Cultured conceptus (EHF/4). (F) Six-somite pairs (6-s). BMP4 is now present throughout the allantois, including endothelium within the core. (G) Sixteen-somite pairs (16-s), BMP4 is present at the chorio-allantoic fusion junction. (H) Cultured conceptus (3/13); BMP4 is present in both mesothelium and in endothelial elements within the core. (I) Twenty-hour allantoic regenerate (3/14) demonstrates a similar BMP4 staining pattern in the allantois as that shown in H. (J-M) Time course of allantoic regenerates created from EHF-stage conceptuses shows BMP4 in the regenerates at (J) 0 hours, (K) 1.5 hours, (L) 3.0 hours and (M) 6.0 hours after allantoic removal. Arrows in J-L indicate the distal site of allantoic regeneration. Abbreviations as in Figs 1, 2. Scale bar in M: 50 µm (A-C,J-M); 100 µm (I); 150 µm (D-G); 200 µm (H).