Imaging the formation of an hematopoietic niche

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Stem cells are necessary for tissue homeostasis, and are often localized to specialized niches that control their function. In this manner, niches control virtually all aspects of stem cell dynamics, properties essential to tissue maintenance. Recent work has shown that precise cellular architecture is important in order for a niche to communicate with fidelity to the stem cells it controls. A major issue is that the field does not fully understand how niches are initially formed in a tissue, nor the key cell biological steps that cause a group of cells to create an effective niche, nor how that organization impacts stem cell regulation. Our lab recently made significant advances on such questions working on the testis niche. In particular we used live-imaging to define the dynamic steps in Drosophila gonadal niche assembly. These observations led directly to a series of experiments revealing a mechanistic understanding of the assembly of this niche. Insect hematopoiesis closely parallels our innate immune system, using several conserved factors important for specifying macrophage-like and anti-microbial-producing cells. The progenitors for these immune cells are controlled by a niche called the Posterior Signaling Center (PSC). Work of others using fixed embryos and end-point analysis showed that the PSC is derived from a cell cluster that must migrate to take up its proper position and begin functional as a niche. How the pro-niche cells navigate to the correct position and assemble into a functional niche is unknown. We propose here to develop tools to address these questions. We will build tools to lineage-label the PSC at an early-enough stage to visualize its construction in vivo. This includes the construction of transgenic lines that should confer spatial and temporal optogenetic control for labeling and real-time visualization. These same tools would enable follow-up experiments to expore the mechanisms underlying niche assembly. We will additionally profile the transcriptional landscape of PSC cells in order to identify new markers aiding investigation of PSC morphogenesis. Collectively, our approaches should provide us with the reagents and preliminary results to support a substantive, longer-term grant proposal addressing underlying mechanisms directly.