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The ability to regenerate organs and tissues has long fascinated research scientists. This is particularly interesting in light of the lack of conservation of regenerative abilities during evolution. For example, a salamander can regenerate an amputated limb, but a human cannot. Dr. Stefano Tiozzo, a postdoctoral scholar in the Anthony De Tomaso lab at University of California, Santa Barbara, recently received the prestigious 2009 Nikon Fellowship, awarded by Nikon Instruments Inc., to explore this phenomenon, and in particular, the cellular and molecular aspect of regeneration.

All multicellular organisms originate from a small set of totipotent embryonic cells: descendants of the fertilized egg that have the ability to expand and differentiate into a structured body plan during embryogenesis. However, fully developed organisms are not static entities, and during normal growth and aging, or after injury, differentiated cells, tissues and organs must be replenished and regenerated.

In adults, this process of regeneration is thought to be carried out either by transdifferentiation or via stem or progenitor cells, which retain the capacity to proliferate, differentiate and/or home throughout the lifespan of the individual. Interestingly, the degree to which different organisms can regenerate tissues and organs is not a conserved feature throughout evolution (e.g. a salamander can regenerate an amputated limb, but a human cannot).

To explore the cellular and molecular aspect of regeneration, Dr. Tiozzo and his research colleagues, Dr. Rendulic and Dr. Kuern, focused on an accessible model organism: the primitive chordate, Botryllus schlosseri. Botryllus schlosseri is a laboratory-reared colonial ascidian and the closest relative to vertebrates that can regenerate its entire body, including all somatic tissues and the germline, every week.

Botryllus has the unique capability to lead to an adult body plan through three completely different developmental pathways: embryogenesis/metamorphosis, vascular budding and blastogenesis. Dr. Tiozzo and his research colleagues specifically aimed to study the source of regenerative plasticity by looking at the cells and tissues involved in the early stages of the two budding processes: vascular budding and blastogenesis. The aim was to be able to recognize the cell population(s) responsible for the bud initiation and to collect molecular clues. This information would help resolve if plasticity of regeneration in basal chordates is due to niche formation/pluripotent stem cells homing or transdifferentiation of pre-existing somatic cells, or both processes simultaneously. The ultimate goal is to understand the source of the regenerative plasticity that characterizes the class of Boryllidae and, eventually, define which molecular pathways have been lost in evolution of the regenerative process.