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The study of stem cell niches in mammalian systems presents an 'arduous endeavor'; in comparison, the fly germarium is relatively easy to manipulate. In the 1990s, H. Lin, A.C. Spradling, and others used of a number of approaches to study Drosophilia GSCs and their niche, including killing specific cells in the germarium with precisely directed lasers; transplantation of cells from the ovary of one fly to another; and genetic perturbations that included the dialing up or down of Hh pathway signaling. The researchers found that following laser ablation of cells surrounding the GSCs - that is killing the niche cells - all the GSCs went on to form eggs, and the system was quickly depleted of its GSC reserve. Moreover, through genetic analyses the researchers identified specific genes required in the niche cells to maintain GSCs within the niche, as would be deduced for a gene that, when disrupted in niche cells, has the same effect as laser ablation of those cells. These studies are credited with providing the first clear experimental evidence of a stem cell niche, as well as defining what genes - what signaling pathways and other cellular activities - are important to the process. Many of the same pathways relevant in other cell types proved relevant to communication between the niche and GSCs, including the Hh pathway. The genes required for suppression of transposon mobilization by the piRNA system also have relevance to the GSC niche; disruption of the piwi gene, for example, can lead to uncontrolled proliferation of GSCs.
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Stephanie Elizabeth Mohr (First in Fly: Drosophila Research and Biological Discovery)