Fig. 11. VCAM1 immunostaining of isolated whole allantoises and allantoic subregions after 24 hours of culture. Subregions of whole lacZ/+ donor allantoises were placed into the exocoelomic cavity of wild-type hosts (A-C,G-I), cultured for 24 hours, exposed to X-gal and VCAM1 immunostained (brown color). Wild-type allantoic subregions were cultured in isolation (D-F). Sections were counterstained with nuclear fast red (A-C,G-I), or hematoxylin (D-F). (A) Donor distal allantoic 2/3 has fused with the host's allantoic regenerate (al-r) and chorion exhibits VCAM1. (B) Donor proximal allantoic 1/3 is tethered to the host's allantoic regenerate (al-r) and exhibits robust VCAM1. (C) Donor proximal allantoic 1/3 is fused with both the host's yolk sac (ys) and chorion (ch) and exhibits robust VCAM1. (D-F) Wild-type distal 2/3 (D), wild-type proximal 1/3 (E), and whole wild-type allantois (F) from headfold (HF)-stage conceptuses were cultured in isolation for 24 hours; all exhibit robust VCAM1. (G) Donor distal allantoic 1/3 exhibits VCAM1 and is fused with the host's chorion. (H) Donor proximal/mid-allantoic region (p+m) is free-floating in the host's exocoelom and exhibited VCAM1 throughout the explant. (I) Donor whole allantois is fused with the host's chorion and exhibits strong VCAM1. In A-C, stages of synchronous donor allantoises and host conceptuses before and after culture are separated by a `/'. In G-I, initial stages of the asynchronous donor allantois and host conceptus are separated by `/', whereas the number after `//' indicates the final stage of the host after 24-hour culture. Scale bar in I: 50 µm (B); 75 µm (D-F); 100 µm (A,C,G-I).