Segment Specific Head Regeneration in the Fresh Water Oligochaete, Lumbriculus variegatus

Karen Crawford

St. Mary's College

The California Blackworm, Lumbriculus variegates, is a robust and inexpensive system for studying the cellular and molecular mechanisms of pattern formation in both epimorphic and morphallactic regeneration. Normally, epimorphic regeneration from any anterior amputation site along the body axis of Lumbriculus results in the formation an 8-segment head and prostomium. Following this, morphallactic regeneration occurs within the body segments adjacent to the new head. Interestingly, level specific amputations within the 8-segment head region most often result in the replacement of only those segments that were removed. Moreover, wounds made within the head region may induce a supernumerary head to regenerate. When this occurs, these heads form only the segments anterior to the wound site. In contrast, regeneration from any posterior amputation site results in the formation of a pygidium or growth zone that continues to add segments indefinitely to the tail of the worm. These results indicate that regeneration within the head is precisely regulated.

To begin to understand the cellular and molecular mechanisms that regulate head regeneration in Lumbriculus, antibodies to the proteins of several segment polarity genes and proteins important to patterning in other organisms were used to probe anterior and posterior regenerating worm fragments. Results from these studies indicate that the protein β-catenin (homologue of Drosophila Armadillo and member of the Wnt-signaling pathway) was expressed in the segments just behind the regenerating head blastema but not the regenerating tail. To explore whether β-catenin might be involved in early patterning in anterior or posterior regeneration in Lumbriculus , freshly amputated worm fragments were allowed to regenerate in the presence of 5, 10 or 20mM LiCl. Regenerating worms cultured in the presence of LiCl exhibited a dose dependent inhibition of head and tail regeneration. Interestingly, tail regeneration was especially affected by LiCl treatment. This response was partially rescued when treated worms were washed free of LiCl. These results suggest that a LiCl sensitive pathway, perhaps associated with the Wnt-signaling, may be responsible for patterning during regeneration in the California Blackworm.