Fig. 5. Localization of VCAM1, cytokeratins and FLK1 in 6-hour allantoic regenerates. Allantoises were removed and operated conceptuses were cultured for 6 hours. Embryo stages before and after culture are indicated at the bottom of each panel (A,C-H), and are separated by `/'. Immunostain is brown in all panels; all sections were counterstained in hematoxylin. (A) Allantoic regenerate (al-r), 3/6-somite pairs, VCAM1-immunostained. This regenerate was less than 220 µm long and was negative for VCAM1 (i.e., no brown staining). Arrowhead indicates mesothelium. (B) Internal control, same conceptus as A, confirms the presence of VCAM1-positive cells in the heart (surrounding the asterisk) (Gurtner et al., 1995; Kwee et al., 1995). (C) VCAM1-stained unoperated cultured control allantois (al) from the same experiment as the specimen in A,B. (D) Brightfield photomicrograph shows cytokeratins (arrows) in both the allantoic mesothelium and core cells of the 6-hour regenerate (al-r). (E-H) Brightfield photomicrographs show FLK1 in the 6-hour regenerates (E,G) and corresponding unoperated cultured controls (F,H). Other abbreviations as in Fig. 1. Scale bar in H: 50 µm (A,B,D-G); 75 µm (H); 100 µm (C).