Figure 2

Splice variants of Xenopus osr2. (A) Schematic representation of the Xenopus osr2 splicing variants A and B based on the mammalian data [35] shows alternative splice sites 2A and 2B indicated by arrowheads. Boxes represent exons and filled areas reflect open reading frames, while lines represent the promoter and introns. In the lower panel a scheme of the five and three zinc-finger domains (grey boxes) in osr2A and in osr2B protein is given, respectively. The black box in osr2B denotes the alternatively spliced exon 4. (B) Alignment of the nucleotide sequence around alternatively spliced exon 4 is based on a Xenopus laevis osr2B full-length cDNA sequence (accession no. BC108579), whereas the corresponding osr2A cDNA of Xenopus tropicalis (accession no. CU075721) is taken, as no corresponding Xenopus laevis cDNA is available. The nucleotide sequence around alternatively spliced sites 2A and 2B (indicated by arrowheads) is conserved in both species. The forward primer FP is identical for both splice variants, whereas the reverse primers distinguish between osr2A and osr2B. (C) Animal caps were cut at the late blastula stage 9 [36] and incubated for 1.5 or 3 hours in retinoic acid (10^-4M) and activin A (10 ng/ml). For 5, 7 and 13 hours treatments retinoic acid and activin A was replaced after three hours with Steinberg's solution as originally described [15]. The mRNA levels were analysed by quantitative RT-PCR using the specific primers for osr2A and osr2B (see Additional file 2) and the results are normalized to odc expression levels. If two independent pools were analysed, the mean is given and the bar marks the two values.