Combinatorial signal integration in the maintenance and renewal of adult germline stem cell fate

Project Summary/Abstract Throughout an organism’s lifetime, adult stem cells (aSCs) play a pivotal role in maintaining tissue homeostasis. aSCs possess the remarkable ability to undergo asymmetric divisions, simultaneously renewing themselves and producing differentiating daughter cells. Unlike aSCs, those daughter cells lack the capacity for self-renewal and instead undergo terminal differentiation. Such divergent cell behaviors – asymmetric division and self-renewal by aSCs versus symmetric division and differentiation by their daughters – suggest that aSCs and their daughters are fundamentally distinct cell types. However, contrary to this model, daughter cells can dedifferentiate to fully regain aSC identity, including a return to stem cell potency. Indeed, dedifferentiation is frequently required to reestablish aSC populations after loss. These phenomena present a fundamental paradox: how can stem cells and their differentiating progeny maintain different behaviors, yet preserve the same potential? Notably, both these exclusively properties are clearly present in germline stem cell (GSC) populations, and are strictly required to maintain species integrity. Drosophila male GSCs are an exceptionally tractable model of aSC biology. In preliminary studies with this model, I discovered that combinatorial integration of two independent signaling factors enables cells to achieve distinct behaviors while maintaining equivalent potency. I refer to this concept as “two-factor authentication,” analogizing stem cell maintenance to cybersecurity. Building on these preliminary discoveries, this proposal aims to comprehensively characterize how adult stem cell systems balance regenerative plasticity with the maintenance of discrete cell behaviors. In Aim 1, I will determine how combinatorial signals from the stem cell niche yield distinct cellular states, including self-renewal, differentiation, and dedifferentiation. In Aim 2, I will determine if GSCs asymmetrically retain a stemness signature that maintains their unique features. Finally, in Aim 3, I will examine the factors involved in reestablishment of GSC fate during dedifferentiation in multiple contexts. Expanding my prior expertise in organismal stem cell biology with advanced bioinformatic and genetic tools will enable the completion of each of these aims. Together, these experiments defining GSC regulation (Aim 1), identity (Aim 2), and regeneration (Aim 3) will allow for a comprehensive assessment of the core requirements to set and maintain these exceptional stem cells.