Fig. 2. X-TSK expression requires BMP signaling. Results of the animal cap (AC) assays. (A-H) Animal caps were prepared from stage 8-9 embryos injected with 0.5 ng Chordin (B,E), 0.5 ng Chordin + 1 ng BMP4 (C,F), 1 ng truncated BMP-receptor (tBR) (H), or none of the above (controls; A,D,G). ACs were harvested at the time equivalent to stage 14 and hybridized with XK81 (A-C) or X-TSK (D-H) probes. Chordin downregulated XK81 expression (B), which was rescued by BMP4 (C). The expression of X-TSK was repressed by Chordin (E), but rescued by BMP4 (F). (H) Truncated BMP receptors repressed the expression of X-TSK. (I) X-TSK expression in a normal embryo at stage 17. (J) RT-PCR analysis with ACs harvested at stages 14 (lanes 1-8) and 17 (lanes 9-16). ODC is used as an internal control. X-TSK expression in the ACs was recovered by increasing amounts of BMP4. BMP4 overexpression induced X-TSK expression at both stages. WE, whole embryo; NI, non-injected ACs.