Background: Among deuterostomes, the regenerative potential is maximally expressed in echinoderms, animals that can quickly replace most injured organs. In particular, sea cucumbers are excellent models for studying organ regeneration since they regenerate their digestive tract after evisceration. However, echinoderms have been sidelined in modern regeneration studies partially because of the lack of genome-wide profiling approaches afforded by modern genomic tools.

Repair and regeneration are key processes for tissue maintenance, and their disruption may lead to disease states. Little is known about the molecular mechanisms that underline the repair and regeneration of the digestive tract. The sea cucumber Holothuria glaberrima represents an excellent model to dissect and characterize the molecular events during intestinal regeneration. To study the gene expression profile, cDNA libraries were constructed from normal, 3-day, and 7-day regenerating intestines of H. glaberrima. Clones were randomly sequenced and queried against the nonredundant protein database at the National Center for Biotechnology Information. RT-PCR analyses were made of several genes to determine their expression profile during intestinal regeneration. A total of 5,173 sequences from three cDNA libraries were obtained. About 46.2, 35.6, and 26.2% of the sequences for the normal, 3-days, and 7-days cDNA libraries, respectively, shared significant similarity with known sequences in the protein database of GenBank but only present 10% of similarity among them. Analysis of the libraries in terms of functional processes, protein domains, and most common sequences suggests that a differential expression profile is taking place during the regeneration process. Further examination of the expressed sequence tag dataset revealed that 12 putative genes are differentially expressed at significant level ( R > 6). Experimental validation by RT-PCR analysis reveals that at least three genes (unknown C-4677-1, melanotransferrin, and centaurin) present a differential expression during regeneration. These findings strongly suggest that the gene expression profile varies among regeneration stages and provide evidence for the existence of differential gene expression.

We have analyzed 5,173 expressed sequence tags (ESTs) from three cDNA libraries of normal and regenerating intestinal tissue of the sea cucumber Holothuria glaberrima and found 22 putative immune-related genes. These sequences showed similarities (e-value approx 10(-8)) to genes involved in immune processes or expressed by immune cells. Sequences were analyzed using bioinformatic tools to determine a putative identity. In addition, phylogenetic analyses were performed to find relationships with similar proteins in other organisms. The mRNAs for ten sequences were detected in coelomocytes by using reverse transcription-polymerase chain reaction (RT-PCR). Moreover, five of them showed a significant increase in expression after an LPS challenge, while the other five showed no significant changes. These results show the variety of immune molecules that may be found in holothurians and support the idea that the invertebrate immune system is more than a collection of simple innate responses. Our study also provides new data of importance in deciphering the evolution and development of the immune system.

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Endometriosis is commonly associated with symptoms similar to those of gastrointestinal diseases, such as inflammatory bowel disease (IBD), leading to erroneous diagnosis and inappropriate management. The role of tumor necrosis factor alpha (TNF) in IBD is well established, but its role in endometriosis--also characterized by the activation of inflammatory mechanisms--is still under study. Furthermore, little is known about the involvement of TNF receptors. Intestinal endometriosis was surgically induced in female Sprague-Dawley rats (n = 10). Control rats (n = 10) received sutures with no implants. Samples of tissue and fluids were collected 60 days after surgery. Endometriotic implants were classified in grades, and the gastrointestinal tract was examined for damage. A significant increase was observed in protein levels of TNF and soluble TNFRSF1B in the peritoneal fluid of experimental rats compared to controls. Expression of Tnf mRNA was significantly increased both in peritoneal leukocytes and in intestinal segments associated with implants in experimental animals. Bioactivity of TNF in tissues was confirmed by overexpression of Icam1, Sele, Vegfa, Flt1 and Kdr. Gene expression of Tnfrsf1a and Tnfrsf1b was downregulated in colon and small intestine of experimental animals, possibly as a mechanism of protection against TNF cytotoxicity. Significant overexpression of genes encoding TNF receptor-associated factors that have been linked to activation of antiapoptotic pathways also was observed. Overexpression of TNF and target genes, underexpression of TNF-receptor genes, and increased shedding of TNFRSF1B in this animal model provide further evidence for involvement of the TNF system in the pathogenesis of endometriosis.

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The sea cucumber (Holothuria glaberrima) is an excellent model to study regeneration processes in deuterostomes. H.glaberrima has the ability to regenerate most of its viscera after the process of evisceration, where most of the viscera are expelled from the body. We have showed that apoptosis takes place during intestinal regeneration. Apoptosis, is the result of DNA internucleosomal cleavage, the morphological characteristics are: cell contraction, nuclear pyknosis, chromatin condensation and cell fragmentation. By using the TUNEL assay, where the TdT enzyme catalyzes the addition of Br‐dUTP, labelling the 3′‐OH terminal groups exposed during the internucleosomal cleavage; we identified apoptotic cells by fluorescence microscopy. We showed a peak in the number of apoptotic cells throughout the first week of regeneration and the distribution of apoptotic cells in the different layers of the large intestine (serosa, sub‐mucosa, mucosa and mesentery). Moreover we have now identified the holothurian homologue of the Survivin gene that in vertebrates functions as an inhibitor of apoptosis. Preliminary results have shown a differential expression of this gene during regeneration. Molecular experiments, PCR and In‐situ hybridization are under way to asses the temporal and spatial expression of apoptosis and survivin expression. Our results prove that similar to embryonic development, apoptosis plays an important role during intestinal regeneration. These studies provide a deeper understanding of the process of intestinal regeneration in the sea cucumber and the applications to studies in other animals, including humans.

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