View Program - 63rd Annual Drosophila Research Conference

The follicle stem cell (FSC) niche in the adult Drosophila ovary balances the actions of stem cell self-renewal and output through the guidance of graded extracellular signals. Anterior sources (cap cells, escort cells [ECs]) produce Hh and Wnt pathway ligands, and posterior sources (polar follicle cells [FCs]) produce JAK-STAT pathway ligands. These opposing gradients intersect over the FSC domain, and regulate FSC division and differentiation into quiescent ECs (anterior) or proliferative FCs (posterior) across FSC positions. We have previously shown through combined lineage and morphological studies that adult ECs, FSCs, and FCs derive from intermingled cell (IC) precursors present at the start of pupation, and acquire their adult function based on their final anteroposterior (AP) location, rather than a series of cell fate decisions. Our studies also revealed how the first FCs and egg chamber are formed. Precursors accumulate posterior to germline and ICs of the developing germarium. These Extra-Germarial Crown (EGC) and Basal Stalk (BS) cells are then invaded by the most posterior germline cyst without any attached ICs, and surround this cyst in an epithelial monolayer. Here we investigate how signaling pathways influence somatic cell AP locations and adult fates during pupal development. Wnt signaling initiates early from the anterior. MARCM lineage studies showed that cells with elevated Wnt pathway activity are biased towards more anterior locations, while reduced Wnt signaling favored more posterior locations. Detectable JAK-STAT signal was seen only after budding of the first pupal egg chamber, when polar FCs are specified. Loss of JAK-STAT signaling favored more anterior locations. Elevated JAK-STAT signaling increased precursor output, suggesting faster division. Hh signaling has previously been demonstrated to begin before pupal development and to be important for generating adult somatic cells of the ovary. Preliminary results suggest that Hh signaling during pupal stages is required for ovarian somatic cell survival and proliferation, with effects on cell location still to be determined. We are particularly interested in exploring which signals affect formation of the first FCs because that process occurs in a different morphological setting to the conversion of adult FSCs to FCs.

Signals governing pupal development of ovarian Follicle Stem Cells and Niche Cells