Expression of Wnt9, TCTP, and Bmp1/Tll in sea cucumber visceral regeneration.

We employ non-radioactive in situ hybridization techniques, which combine good tissue morphology preservation with high sensitivity of transcript detection, to map gene expression in the regenerating digestive tube of the sea cucumber Holothuriaglaberrima. We investigated localization of transcripts of Wnt9, TCTP, and Bmp1/Tll, the genes that have been previously known to be implicated in embryogenesis and cancer. The choice was determined by our long-term goal of trying to understand how the developmental regulatory pathways known to be involved in tumor development can be activated in post-traumatic regeneration without leading to malignant growth. The gene expression data combined with the available morphological information highlight the gut mesothelium (the outer layer of the digestive tube) as a highly dynamic tissue, whose cells undergo remarkable changes in their phenotype and gene expression in response to injury. This reversible transition of the gut mesothelium from a complex specialized tissue to a simple epithelium composed of rapidly proliferating multipotent cells seems to depend on the expression of genes from multiple developmental/cancer-related pathways.