For a proposed animal-free medium, the UCSD study takes advantage of a previously unidentified soluble factor this is secreted from mouse feeder layers to maintain stem cells' undifferentiated state and pluripotency, the ability to become all tissue types in the body. The scientists knew that a cocktail of various growth factors and chemicals had previously been shown to modulate cellular growth and differentiation in human pancreatic cells. Human embryonic stem cells cultured for several weeks under these conditions showed no change in cell form and structure. The team then eliminated each factor and pluripotency was assessed. At first, the results were narrowed to three molecules, with activin A, a protein that participates in cellular growth and differentiation, as well as hormone secretion, finally shown in additional testing to maintain the undifferentiated state.
The study's first author, Gillian M. Beattie, M.S., UCSD Department of Pediatrics and the Whittier Institute, said that "it will be rather simple now to develop a specific defined medium that allows for the maintenance of the human stem cells and enhances research without the problem of contaminating animal cells and their products."
In a summary to their paper, the researchers noted that "the identification of activin A as a key factor in mediating these cellular events will help to unravel the biochemical pathways responsible for 'stemness'. An increased efficiency in the generation and culture of human stem cells for potential clinical applications is timely, given the recent report of 17 newly derived stem cell lines available for non-federal research. The findings here may facilitate the derivation of new human embryonic stem cell lines without the use of animal or human feeder layers."