"There are colonies of pelagic tunicates which have taken shape like the finger of a glove. Each member of the colony is an individual animal, but the colony is another individual animal, not at all like the sum of its individuals... So a man of individualistic reason, if he must ask, "Which is the animal, the colony or the individual?" must abandon his particular kind of reason and say, "Why, it's two animals and they aren't alike in any more than the cells of my body are like me. I am much more than the sum of my cells, and, for all I know, they are much more than the division of me.'"
John Steinbeck, The log from the Sea of Cortez.
Understanding the ability to regenerate organs and tissues is the long-term goal of research into stem cell biology and regenerative medicine. This is particularly interesting in light of the lack of conservation of regenerative capabilities during evolution: a salamander can regenerate an amputated limb but a human cannot. Colonial chordates provide experimentally accessible and reliable regenerative potential that can facilitate our understanding of the biology underlying regeneration. Colonial ascidians such as Botryllus schlosseri are the closest relatives to vertebrates that, beside embryogenesis, can adopt distinct developmental pathways ( ‘palleal budding’ or blastogenesis and ‘vascular budding’) to regenerate their entire body, including all somatic tissues and the germline. Our research aims are: (A) to understand the source of this regenerative plasticity, focusing on the molecules, cells and tissues involved in the early stages of the two budding processes and, (B) to understand patterning and axis formation during regeneration at the molecular and morphological levels, and compare the mechanisms involved with those of embryogenesis. The long term goals are to uncover the source of the regenerative plasticity that characterizes the class of Botryllidae. It is also our interest to understand how, in a single organism, the formation of same structures is achieved through morphologically different developmental stages. The latter aspect can provide insights on the plasticity and on the co-option of basic molecular mechanisms involved on body patterning.