David L. Stocum, Ph.D. Department of Biology and Center for Regenerative Biology and Medicine Indiana University-Purdue University Indianapolis

My research is focused on how patterns of tissue organization are maintained after being established during ontogenesis, and how they are reconstituted in the face of damage due to injury or disease. This maintenance and repair is called regeneration. The model I use for the study of regeneration is the salamander limb, which regenerates by the dedifferentiation of myogenic, skeletal and connective tissue cells local to the wound surface into stem cells that proliferate to form a blastema. I have shown that the blastema self-organizes the tissue patterns of the regenerating limb parts; i.e., the pattern-forming signals are generated within the blastema, not from differentiated tissues adjacent to it.

Experiments from my laboratory have shown that the signals that generate pattern in the regeneration blastema are dependent on, and deployed within, an outline of boundary positional identities that are inherited by blastema cells from their parent cells of origin. These boundaries are circumferential, proximal and distal. By means of cell sorting assays in vitro and in vivo, we have shown that boundary positional identities are encoded in the molecular structure of the cell surface. The boundary positional identities provide a context within which any missing parts of the pattern to be regenerated can be filled in by cell division and intercalation of any missing identities.

This work has led to the formulation of a model for limb regeneration based on the idea that a crucial early event in regeneration is the establishment of a distal boundary tandem to the proximal boundary (Nye et al, 2003). The proximal and circumferential boundaries are represented in the earliest dedifferentiated cells, being inherited from parent differentiated cells at the level of amputation. The distal parts of the limb, however, have been removed, making it necessary to re-establish a distal boundary. That the distal boundary is re-established quickly is indicated by the fact that molecular markers for both distal and proximal boundaries are both expressed throughout the very early blastema (Gardiner et al, 1995). Subsequently, the two markers separate so that the distal marker is confined to the region from which the new hand will form. It is not known how this segregation, which would be crucial for the intercalation of the intermediate pattern, is accomplished. My hypothesis is that the wound epidermis that covers the blastema plays a role in this segregation.

A major question is whether the generation of signals by boundary regions is a general mechanism employed for the generation of tissue patterns during ontogenesis, as well as a mechanism for regenerating structures such as appendages.

In addition to this specific research interest, I also have general interests in regenerative biology and medicine. I have designed a one-semester course on this subject and have written a number of review papers on the subject (Stocum, 2002, 2003).