Verification of the differential expression of X. tropicalis transcripts identified by SAGE. (a) Total RNA was obtained from dorsal (DMZ) and ventral (VMZ) explants isolated from gastrula stage X. tropicalis. RT-PCR was performed using specific primers for each transcript. DV01 (pintallavis), DV03 (vent-1.1), chordin and sizzled were included as controls. (b) X. tropicalis embryos at stage 10 (a-i, a'-i'), and stages 18-20 (a"-i") were processed for in situ hybridization with specific probes for each transcript. (a'-i') Hemi-sections from embryos at the gastrula stage. (a-i, a'-i') Dorsal to the left and (a"-i") anterior is up. The frequency of occurrence in each library is indicated in parentheses below the name for each transcript (tag frequency in dorsal library; tag frequency in ventral library).