Project Summary/Abstract: Stem cells are required for tissue homeostasis and regeneration. Accomplishing these tasks often requires intimate association between stem cells and their niche, where stem cells efficiently receive critical niche- derived signals within specialized tissue compartments. These niches are formed by cells that often must migrate during organogenesis to attain their appropriate position, yet how this morphogenesis is achieved is unclear. The broad objective of this application is to define – using powerful genetics and incisive optogenetic approaches in an accessible undergraduate model system – the molecular mechanisms dictating embryonic establishment of the Drosophila male testis niche. Results from this work will reveal the cellular dynamics and molecular mechanisms required to assemble a functional model stem cell niche, which are likely to be applicable to the numerous other stem-cell based tissues. Our previous work showed that Slit and FGF signals from adjacent visceral muscle are required to assemble the testis niche. In response to these signals, niche cells express the transcription factor islet, which is required for F-actin polarization and movement to the gonad anterior. In Aim 1, we will examine key signaling intermediaries required to induce islet expression in response to gonad extrinsic signaling. In Aim 2, we will define downstream mechanisms that mediate islet function and pursue predicted islet targets expressed in niche cells. Using an optogenetic approach during in vivo live imaging, we will also investigate niche cell behaviors reliant upon mechanisms regulating the F-actin cytoskeleton. In Aim 3, we will identify how niche-extrinsic signaling from another tissue within the gonad positions the forming niche. Concepts we elucidate will have broad applicability to studying normal development, promoting success of stem cell replacement therapies, and revealing mechanisms by which cancer cells often shape their unique tumor microenvironments. Furthermore, funding from this proposal will support infrastructure at a large regional public university where we will employ a tractable model system that provides high-impact biomedical research experiences to underserved undergraduates in a supportive training environment.

Project Narrative: The positioning and architecture of a stem cell niche is crucial to the niche's ability to maintain stem cells and thus, to maintain appropriate tissue renewal during injury or aging. The mechanisms by which niches are assembled, however, remain poorly characterized. Using a powerful genetic model, this proposal will investigate the molecular mechanisms required to assemble a stem cell niche, which is required for development and maintenance of functional biological tissues.