Transcription factor Pbx4 is recruited to form dimeric or trimeric complexes with Hox and/or Meis homeodomain proteins and participates in patterning the hindbrain and retina during vertebrate CNS development. We characterized a Pbx4 cDNA isolated from a Gekko japonicus brain and spinal cord cDNA library. Northern blot and quantitative real-time PCR revealed that gecko Pbx4 was ubiquitously expressed in several tissues. In the spinal cord after tail amputation, in situ hybridization results showed that Pbx4 mRNA staining was present in the gray matter and ependymal cells of the spinal cord but that additional staining was seen in the white matter in regions close to the amputation stump. Both in situ hybridization and real-time PCR methods detected no obvious changes in Pbx4 expression in segment of the cord farthest from the amputation site, however, Pbx4 mRNA expression increased by 2 fold in segment close to the amputation site after 2 wks. The upregulation of Pbx4 was inhibited by an intraperitoneal injection of retinoic acid (RA) (100 microg/g body weight). These results suggest that gecko Pbx4 is possibly involved in spinal cord regeneration at sites of proximal amputation, and that the expression of Pbx4 in the spinal cord is regulated by retinoic acid in a manner different from that of Pbx1, Pbx2 and Pbx3.