The research conducted by Spradling--a Howard Hughes Medical Institute Investigator-- and colleague Dr. Toshie Kai, involved so-called germline stem cells of the female fruitfly. These cells are precursors to eggs and begin their journey as stem cells living in a special environment called a niche. In the niche, a stem cell splits into two daughter cells, one of which leaves the niche to begin its transformation. Through a series of 4 divisions a cluster of 16 cells forms--an immature egg with 15 accompanying nurse cells. The researchers discovered that the cells in clusters of 4 and 8 cells can still return to the stem-cell state under appropriate conditions. Moreover, the reverted stem cells worked as well as normal stem cells. Flies with only reverted stem cells were as fertile as normal flies throughout adult life.
"For most stem cells, it has not been possible yet to determine how quickly their progeny cells lose the ability to function again as stem cells," Spradling noted. "In the fruitfly (Drosophila) ovary we could directly test this and found conditions where the cluster cells reverted to a stem-cell state and functioned throughout the entire life of the adult. We don't know yet if this will be a general result that applies to other stem cells," cautioned Kai. "The progeny of germline stem cells might develop relatively slowly compared with other stem cell progeny, and thus retain their 'stemness' longer."