Characterization of the Xenopus homolog of animmediate early gene associated with cell activation: sequence analysis and regulation of its expression by thyroid hormone during amphibian metamorphosis

The complex transformation of a tadpole to a frogduring amphibian development is under the control of thyroid hormone (T3). T3 is known to regulate gene transcription through its nuclear receptors. We have previouslyisolated many genes which are up-regulated by T3 in theintestine of Xenopus laevis tadpoles. We have now cloneda full- length cDNA for one such gene (IU12). Sequenceanalysis shows that the IU12 cDNA encodes a plasmamembrane protein with 12 transmembrane domains andhomologous to a mammalian gene associated with cell activation and organ development. Similarly, we have foundthat IU12 is activated during intestinal remodeling whenboth cell death and proliferation take place. Furthermore,IU12 is an early T3-response gene and its expression in theintestine during T3-induced metamorphosis mimics thatduring normal development. These results argue for a roleof IU12 in the signal transduction pathways leading to intestinal metamorphosis.