Pygospio elegans: Breaking the rules of regeneration
LE3 .A278 2007
Gibson, Glenys D.
Bachelor of Science
Regeneration is the ability to replace lost structures and thereby restore the original body plan. Work on common models such as hydra and salamanders suggests that cells within a regenerate receive positional information (e.g., anterior, ventral) from gradients of morphogens that originate from an organizing centre. The major models also suggest that regeneration follows two basic rules: distalization in which regeneration occurs from proximal to distal, and intercalation, in which elements missing from within a pattern are also restored. I am developing a new model of regeneration based on the polychaete Pygospio elegans Webster, a worm that can regenerate both anterior (thorax and head) and posterior structures (tail and pygidium). I tested the potential of different body regions to either regenerate or inhibit regeneration. The results suggest a model with both anterior and posterior organizing centres that are activated by tissue damage; however, the potential for activation is dependent upon location within the body. While distalization does occur, intercalation does not as the organizing centres are incapable of regenerating the abdomen. The abdomen has the greatest potential to form an organizing centre and this potential decreases peripherally to a lack of potential in the head and tail. The tail appears to inhibit activation of the posterior organizing centre. Formation of the anterior blastema suggests that morphogen gradients assign positional value to the proliferating cells and assures high fidelity to the restoration of the entire region (61% of original segments are replaced, n=140). A morphogen gradient model also applies to posterior regeneration. However, once the growth zone and pygidium form, the pygidium appears to act as a morphogen sink. At this point, posterior regeneration stops (only 20% of the original segments were restored, n=140) and in the type of regeneration xiv shifts to morphallaxis. Although similar to blastema formation in salamanders in some regards, my data show that regeneration is quite different in polychaetes and requires further exploration to fully develop and understand this system.
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