Stem cells are necessary to maintain homeostasis within adult tissues. These cells receive signals from their surrounding microenvironment or niche in order to function properly. Precise regulation of stem cells and their niches is vital to prevent depletion or overgrowth of the stem cell pool. Although many mammalian niches have been characterized, the Drosophila testis provides a unique and more accessible system to study the regulation of a stem cell niche in vivo. This well-defined niche consists of a cluster of non-dividing (or quiescent) somatic hub cells that signal to the attached germline and somatic stem cells. Damaging the testis or overexpressing genes that activate the cell cycle in hub cells induces hub cell divisions, but also leads to the conversion of hub cells to somatic stem cells. This change in cell fate is accompanied by the formation of new niches, characterized by the presence of ectopic hubs each supporting active stem cells. Recently I found that the highly conserved cell cycle inhibitor and tumor suppressor retinoblastoma homolog RBF is a critical regulator of hub cell maintenance. Loss of RBF in the hub is sufficient to cause hub cell proliferation, and lineage tracing reveals that RBF prevents hub cells from converting to somatic stem cells. In addition, extended knockdown of RBF in the hub also leads to ectopic niche formation. Live imaging of hub cells undergoing loss of quiescence in multiple conditions indicates that converting hub cells migrate farther distances than their wild-type counterparts. Knockdown of RBF along with its interacting partner (the cell cycle activator E2F) rescues both the over-proliferation and cell fate conversion phenotypes, suggesting that targets of E2F may drive both the proliferation of hub cells and their conversion to somatic stem cells. However, these two phenotypes may be separable. Loss of the transcription factor escargot from hub cells causes them to convert to somatic stem cells (Voog et al., Cell Reports 2014), and my preliminary data suggest that Escargot does not prevent loss of hub cell quiescence or ectopic niche formation. Thus, RBF works through the canonical cell cycle pathway to actively regulate hub cell quiescence and identity, and likely acts upstream of escargot and additional factors during this process. This work provides a model for understanding the regulation of niche cell quiescence and identity, which could be pertinent in other stem cell niches to prevent over-proliferation and metastases. .