Interactions between axon-like projections extended byDrosophilaFollicle Stem Cells dictate cell fate decisions

Stem cells cycle between periods of quiescence and proliferation to promote healthy tissue aging. Once proliferation is initiated, mechanisms that control the balance between self-renewal and differentiation must be engaged to ensure maintenance of stem cell pools until the next quiescent cycle occurs. Here, we demonstrate that dynamic axon-like projections extended by Follicle Stem Cells (FSCs) in the Drosophila ovary control the self-renewal-differentiation balance. Known axon growth regulators still life and sickie are necessary and sufficient for FSC projection growth, mediating organization of germline cyst architecture during follicle formation, controlling targeting of projections to FSCs or germ cells, and regulating expression of the cell fate determinants Eyes Absent (Eya) and Castor (Cas). Our results support a model in which FSC projections function similarly to axons, providing structural organization to a dynamic organ while mediating communication between distinct cell types to effect the key cell fate decision to self-renew or differentiate.