A Xenopus homolog of a human p53-activated gene, PA26, is specifically expressed in the notochord

The LIM class homeodomain protein Xlim-1 is specifically expressed in the organizer and later in the notochord in Xenopus. By seeking genes which are activated by Xlim-1 in animal caps, we isolated a gene which encodes a protein highly homologous to human PA26-T2, a p53-inducible nuclear factor, which we refer to as XPA26. Northern blot analysis showed that maternal transcripts of XPA26 are detected at cleavage stages and reduced during gastrulation. Whole-mount in situ hybridization showed that zygotic transcripts of XPA26 were initially detected in the anterior portion of developing notochord at neurula stages, and later in the entire notochord except its posterior region at tailbud stages. Thus the zygotic expression of XPA26 was detected exclusively in the notochord.