Maintenance of A/P body regions in planarians by tcen49, a putative cystine-knot neurotrophin

In freshwater planarians, the protein TCEN49 has been linked to the regional specification of the central body region, which includes the pharynx. Here we present the genomic and deduced amino acid sequence of the tcen49, show the expression of tcen49 mRNA and compare the location of its protein in intact and regenerating organisms. The open reading frame encodes a secreted protein of 70 amino acids that shows no similarity to any other known protein, although it displays a cysteine pattern found in some members of the neurotrophic family. In intact adult planarians, transcripts are detected specifically in secretory cells in the central body region, whereas the protein is secreted from them to all the tissues in this region. Neither mRNA nor protein is detected in the anterior or posterior regions. During regeneration, the timing and dynamics of tcen49 expression and TCEN49 location are always detected prior to any morphological evidence of the formation of the new central region, although the protein is not secreted until the pharynx starts its maturation. During anterior regeneration, tcen49 is detected as early as day 1 of regeneration throughout the regenerate, which is different from posterior regenerates. Our results suggest (1) the presence of inhibitory mechanisms that regulate tcen49 expression as well as the post-transcriptional regulation of its RNA and (2) that TCEN49 is not necessary to start regeneration but is involved in regional pattern maintenance.