Regulation of cellular plasticity and regeneration in Drosophila spermatogenesis

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Abstract Many adult tissues replace cells lost due to normal wear and tear through the activity of stem cells, but can use entirely different strategies when injury occurs. The ability to understand and control regeneration, or the regrowth of lost tissues or organs in response to injury, is a long- standing goal in biology. Cells with the capacity to adopt the biological properties of other cell types under specific conditions, or cellular plasticity, are key contributors to regeneration. Stem cells and even differentiated cells can have surprising degrees of plasticity, allowing them to adopt new fates and rebuild damaged tissues. This happens in response to altered microenvironments that arise upon injury, but the mechanisms that regulate plasticity are poorly understood. We have developed the Drosophila testis as a model system to study the biology of stem cells and their microenvironments, or niches. Advantages include the relative simplicity of this tissue and an unparalleled collection of genetic tools to probe it functionally. Previously, we showed that damaging the Drosophila testis converts differentiating germ cells to revert to germline stem cells to repair the tissue. We recently found that quiescent somatic niche cells can transdifferentiate into new somatic stem cells upon damage. Here we combine live imaging, lineage tracing and single cell transcriptomic profiling to determine now niches sense damage and then activate program(s) to regenerate missing stem cells. We will also uncover the overall complexity of the genetic pathways enriched in the testis niche during normal tissue turnover, following up on candidate signals that relay information from stem cells to their niche. Our synergistic approach will enhance the understanding of the fundamental cellular and molecular mechanisms driving homeostasis and regeneration in the testis, which has important implications for understanding fertility, regeneration and cancer.