Title of project

Regeneration in Lumbriculus Embryos is Dependent on Amputation Site Along AP Axis

Faculty Advisor

Kay A Tweeten



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Regeneration in Lumbriculus Embryos is Dependent on Amputation Site Along AP Axis

Lumbriculus variegatus, a freshwater oligochaete, has high regenerative capability. Amputation at all levels along the anterior/posterior (AP) axis of these annelids except for within 20-30 segments of the pygidium generates fragments capable of forming new head segments. New tail segments form from anterior fragments produced by amputation at any point along the AP axis behind the eight head segments. While studying sexual reproduction in a Lumbriculus species collected from a lake in Minnesota, we determined that newly hatched worms were capable of regeneration. Studies by other scientists on rats, mice, and lizards have shown that embryos from these vertebrates formed tissue protrusions after amputation of limb or tail buds. Even though regeneration was partial, with little to no differentiation of mesenchyme, apical ectodermal ridges required for vertebrate regeneration developed in the protrusions. Intrigued by these observations, we conducted amputation experiments on Lumbriculus embryos to investigate their regenerative potential. Lumbriculus embryos were allowed to develop until formation of mouth and prostomium were first observed. At this point, embryos were released from cocoons and anterior or posterior tissue was then removed from the embryos at different levels along the AP axis. The results showed that head and tail segments were regenerated after amputation of embryonic tissues in L. variegatus. The regenerative capacity was dependent on the position of amputation along the AP axis. Following amputation near the ends of embryos, head and tail segments formed. However, when 96-hr embryos were cut in half, posterior fragments regenerated head segments while anterior fragments only showed wound healing. Regeneration in adult animals is dependent on the presence of differentiated cells near the site of amputation that then dedifferentiate and contribute to formation of new tissues. The differentiated cells or signals needed for tail regeneration may not have been present in the mid-body of the L. variegatus embryos at the time of amputation. We conclude that some aspects of regeneration must be distinct from embryonic development in L. variegatus. This annelid offers a unique experimental system in which to study and compare the cellular and molecular mechanisms involved in these processes.