A cnidarian homologue of translationally controlled tumor protein (P23/TCTP).

A protein homologous to P23, or translationally controlled tumor protein (TCTP), was cloned in Hydra vulgaris, the most ancient type of metazoan from which P23/TCTP has been characterized to date. Hydra P23/TCTP is composed of 184 amino acids and is encoded by a single mRNA of 700 bp. This invertebrate P23/TCTP is well conserved compared to those of other invertebrate and vertebrate species. Expression of Hydra P23/TCTP was confirmed by western blot of Hydra cell lysates using a polyclonal antibody against murine recombinant P23/TCTP. Spatial distribution of P23/TCTP mRNA and protein in Hydra was studied using in situ hybridization and immunostaining, respectively. Hydra P23/TCTP expression along the longitudinal body axis is regulated at both the transcriptional and the translational level. High levels of P23/TCTP mRNA were detected in a subpopulation of cells in the body column. In contrast, no mRNA was evident in the differentiated cells of the head and the foot regions. Coincidentally, P23/TCTP protein also concentrates to the body column, with no detectable protein in the head and foot region. However, despite the existence of P23/TCTP mRNA in both the ectoderm and endoderm in the body column, its protein is localized to the endodermal cells, suggesting a regulatory mechanism at the translational level. Taken together, the expression pattern of P23/TCTP in Hydra correlates with regions in which cell proliferation is actively occurring and its expression is excluded from regions where terminal differentiation has occurred.