Fig. 2. (A) Neurosphere transplant (BMP-2 pre-treated) in the chick embryo neural tube 12 hours post transplantation (p.t.) (stage 13, HH) with visible fluorescence signal of the neurosphere. Transplant is located between the 18th pair of somites. (B) Enlargement of the same embryo as in A in paraffin section stained with HNK-1 antibody (brown reaction). SVZ neurosphere cells appear HNK-1 positive, whereas autochthonous chick neural crest cells are HNK-1 negative at this stage in the lower trunk region. (C) Same embryo as in A and B in parallel section. Anti-GFP staining shows integration of SVZ cells into the dorsal neuroepithelium and the roof plate, but transplanted mouse cells and host cells do not intermingle yet. (There is some nonspecific staining in somites.) (D) BMP-2 pre-treated neurosphere 24 hours p.t. in the chick embryo neural tube (stage 19, HH, total incubation time 72 hours). The transplant is located at the region of the upper appendage. GFP-epifluorescence shows bilateral emigration of single cells of the transplant laterally above the projected border of the neural tube. (E) The same embryo as in D. The tangentially cut cryostat section (see insert at lower left for orientation) stained with GFP antibody shows intermingling of mouse and chick cells and single GFP-positive mouse cells in the region of the roof plate (upper right insert). (F) Paraffin section of a different embryo of the same experiment. Emigrated SVZ cells visualized by in situ hybridization with the mL1 probe. Reactive cells can be seen in the dorsal neural tube and at the ventral root.