Developmental Genes in Gut Regeneration of the Sea Cucumber

Abstract

Organ formation as consequence of regenerative events in adult animals has long been thought to involve processes similar to those that take place during embryological development. In previous studies on intestinal regeneration in the sea cucumber, Holothuria glaberrima we have reported the over expression of various development-associated genes. Here we explore whether some of these genes are playing similar roles in intestinal regeneration as they do during embryological formation of the digestive system. Specifically, we determine the expression of the developmental genes Hox1, Hox9, Hox12, Wnt9 and BMP1 along the antero-posterior axis of the normal and regenerating digestive tract. Using RT-PCR, no significant differences in the expression of Wnt9 and BMP1, were found. On the other hand, both Hox1 and Hox12 appeared to be differentially overexpressed; the Hox 1/Hox12 mRNA expression ratio was significantly higher in the anterior regions of the digestive tract than in the posterior regions. This difference in expression correlates with the expected expression gradient that guides Hox gene expression during development. We also used known inhibitors of the Wnt-canonical pathway to determine the possible role of this development-associated gene during the first week of regeneration. The overall result was a delay in the intestinal regeneration process in EGCG inhibited animals when compared with controls, as determined by a reduced size of the regenerating intestinal blastema. Immunohistological experiments using rhodamine-labeled phalloidin and antibodies against collagen and BrdU showed particular effects on the cellular events that underlie intestinal regeneration. Thus, our results show that developmental genes are expressed during intestinal regeneration in H. glaberrima, and that they play roles in intestinal regeneration akin to those observed in embryological development. These results open the door to future experiments to figure out the specific cellular events involved.