The following additional data files are available with the online version of this paper.

Additional data file 1 includes Supplementary Tables 1-4 and their legends. Supplementary Table 1 contains the tags derived from known genes with differential expression along the dorso-ventral axis and their frequency of occurrence in our SAGE libraries. Supplementary Table 2 contains the tag-mapping to transcripts for the 125 tags with significant difference of frequency of occurrence between both libraries. Supplementary Table 3 contains reverse SAGE sequences. Supplementary Table 4 contains the sequences of the primers and information about the probes used in this study. 

Additional data file 2 is a table containing the list of 180 tags with p-values < 0.05 (obtained with the 3 statistical tests), information about known genes and count fold-ratios.

Additional data file 3 corresponds to Supplementary Figure S1 including RT-PCR for DV11 and DV17 in dorsal and ventral explants of X. tropicalis. 

Additional data file 4 contains the complete list of experimental tags with their frequencies of occurrence in the SAGE libraries, normalized count ratio and p-values from three different statistical tests. 

Additional data file 5 contains 15-nts tag sequences, their frequencies in the SAGE libraries, count ratios, p-values and their corresponding sequences of 14-nts tags.

Additional data file 6 contains the list of experimental tags matching to the genome and to the Ensembl transcripts in positions 1, 2 or polyA-next. 

Additional data file 7 contains the list of experimental tags matching to the genome, to the NCBI, Unigenes and Gurdon transcript databases in positions 1, 2 or polyA-next (only those not present in Ensembl). 

Additional data file 8 contains the list of experimental tags matching to the genome but without reliable matches to the transcript databases. 

Additional data file 9 contains the list of experimental tags matching to the genome but without any match to the transcript databases. 

Additional data file 10 contains the list of experimental tags matching to the genome and their frequencies of occurrence in the transcript databases used in this study. 

Tag-mapping of experimental tags to the transcript databases are included in Additional data file 11 (Ensembl), Additional data file 12 (NCBI), Additional data file 13 (Unigene) and Additional data file 14 (Gurdon).