Tissue regeneration has intrigued biologists since the eighteenth century. While regeneration has been studied in many species, the cellular and molecular mechanisms governing successful compensation for lost body parts are poorly defined. This dissertation examines the cellular and molecular correlates of a form of regeneration defined as morphallaxis. Morphallaxis does not involve cell proliferation, but instead relies on the reorganization of existing tissues to recover body structure and function. Morphallaxis is a mechanism used during segmental regeneration (i.e., head or tail replacement) by the aquatic oligochaete, Lumbriculus variegatus. Here, morphallaxis of the nervous system is documented during segmental regeneration of Lumbriculus and during asexual reproduction. The morphallactic processes, which underlie changes in the neural anatomy and physiology of these worms, are reminiscent of mechanisms utilized by other neural plasticity events, including learning and memory. Proteomic and biochemical studies focus on a molecular marker of neural morphallaxis. The expression patterns of morphallaxis-associated-protein 66, MP66, are differentially regulated during both regeneration and asexual reproduction. This expression patterncorrelates with time-points of major cellular changes associated with neural morphallaxis. Thus, cellular and molecular events, demonstrated as part of neural morphallaxis in Lumbriculus, are recruited in two life-history contexts. Chemical disruption experiments, where either segmental regeneration or asexual fission are blocked, reveal that morphallaxis can be mechanistically dissociated from regeneration and reproduction. These results set a foundation for future investigations of specific mechanisms that mediate this novel form of neural plasticity.

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