Fig. 3. Apoptosis in the ICM and cells of the dorsal trunk and tailbud. (A) Acridine Orange staining of wild-type and bls embryos at 15- somites and 23 hpf detects cells undergoing apoptosis. Images of embryos under light-microscopy (far left and far right) are shown as anatomic references for the fluorescence images (middle left and right). Apoptotic cells appear as yellow dots when stained with Acridine Orange. Low level apoptosis is can be seen in wild-type embryos (sparse yellow dots). However, bls embryos exhibit marked apoptosis in the ICM (arrowhead) and dorsal trunk mesenchyme (arrowheads with asterisk). The numerous apoptotic cells line the dorsal trunk of the bls embryo, and extend around the tailbud into the ICM. (B) Transcripts of spt can be detected in the ICM at 23 hpf in wild-type but not bls embryos (arrowhead). Expression of spt in the tailbud and spinal neurons are unperturbed by bls. Likewise, tbx6 expression is absent in the ICM of bls mutants, but is normally expressed in the tailbud. Neural crest derived Rohon-Beard cells are detected with HNK-1 antibody along the dorsal trunk of both wild-type and bls embryos (arrowhead). Axial mesoderm markers ntl and shh exhibit wild-type expression patterns in bls notochord and tailbud.
