Affiliation: Johns Hopkins University School of Medicine, Baltimore, MD
Keywords: b. germline stem cell; b. death mutants/genes
Stem cells are integral to the development and maintenance of a tissue. Adult stem cells have the unique ability to self-renew and produce differentiated daughter cells and have been shown to survive radiation-induced DNA damage in many tissues. However, the exact pathways these cells use to repair DNA damage in an intact tissue are not very well understood. Here we use the Drosophila testis stem cell niche to understand the processes of DNA damage response in an intact niche. Germline stem cells (GSCs) give rise to sperm in the Drosophila testis and have been shown to resist high (75 Gy) irradiation (IR), while their differentiating progeny, spermatogonia die. The radio-resistance of the GSCs suggests that they efficiently and successfully use the DNA double-strand break (DSB) repair pathways, non-homologous end joining (NHEJ) and homologous recombination (HR). Our goal is to understand the specific mechanisms GSCs use to resist IR induced damage and maintain tissue homeostasis. Preliminary data suggest that the response of GSCs to IR in flies null for NHEJ is phenotypically indistinguishable from wild type, but flies null for HR are more sensitive to IR. We hypothesize HR is required for damage-induced regeneration and that the ability of the GSCs to survive irradiation depends on its cell cycle phase at the time of irradiation, which dictates the DSB repair pathway used. To test this, we are using Drosophila-specific fluorescent ubiquitination-based cell cycle indicator (fly-FUCCI) system to visibly mark the stages of the cell cycle in live and fixed imaging, providing an in-depth analysis into the survival mechanisms carried out by IR-damaged GSCs. A deeper understanding of stem cell resistance to IR will add greatly to the Drosophila testis field and may have implications in other radio-resistant stem cells, such as cancer stem cells.