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

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Abstract
The complex transformation of a tadpole to a frog during amphibian development is under the control of thyroid hormone (T3). T3 is known to regulate gene transcription through its nuclear receptors. We have previously isolated many genes which are up-regulated by T3 in the intestine of Xenopus laevis tadpoles. We have now cloned a full-length cDNA for one such gene (IU12). Sequence analysis shows that the IU12 cDNA encodes a plasma membrane protein with 12 transmembrane domains and homologous to a mammalian gene associated with cell activation and organ development. Similarly, we have found that IU12 is activated during intestinal remodeling when both cell death and proliferation take place. Furthermore, IU12 is an early T3-response gene and its expression in the intestine during T3-induced metamorphosis mimics that during normal development. These results argue for a role of IU12 in the signal transduction pathways leading to intestinal metamorphosis.