Figure 2. Activation of EGFR signaling in adult hub cells causes them to convert to CySCs.

(A–D) Single confocal sections through the apex of testes after 8 days of G-TRACE lineage tracing system expression in adult hub cells. Testes were immunostained for RFP (red fluorescent protein, marking current expression of the hub-specific driver E132-Gal4) and GFP (green fluorescent protein, marking both current and past expression of E132-Gal4) and counterstained with DAPI (blue; marks all nuclei). Hubs are outlined in white. (A'-D') Red channel alone, in white; (A"-D") green channel alone, in white. In control testes (A), hub cells expressing the G-TRACE system alone are marked with RFP and GFP, but no cells outside the hub are marked. In testes over-expressing components of the EGFR signaling pathway in the hub together with G-TRACE (B–D), hub cells are marked with RFP and GFP, and cells outside the hub are also marked, either with GFP and low levels of RFP (yellow arrowheads) or with GFP only (white arrowheads). The marked cells outside the hub appear to be cyst lineage cells that arose by conversion of hub cells to CySCs, which no longer express RFP once they lose their hub cell fate. Scale bar in D, for all panels, is 10 μm.