Figure 1. The effect of aging on germ line dedifferentiation in the Drosophila testis.

(A) Schematic of early spermatogenesis and the Stat92E^ts reversion paradigm. GSCs (light green) and cyst stem cells (CySCs, light gray) surround the hub (red). A pair of CySCs envelopes each GSC, while cyst cells (dark gray) envelope gonialblasts and spermatogonial cysts (dark green). Red dots and branched structures represent a germ cell-specific organelle called the fusome. Jak-STAT signaling is required for stem cell maintenance. In flies carrying the temperature sensitive allele of Stat92E, GSCs differentiate at the restrictive temperature (29°C). Upon recovery at the permissive temperature (18°C), spermatogonia revert to GSCs. (B–G′) Immunofluorescence images of testes stained for Fasciclin3 (Fas3) (hub; red), alpha-spectrin (fusomes; red), and Vasa (germ cells; green) during dedifferentiation. (B-B′,E-E′) Spectrosomes (arrowheads) within GSCs and branched fusomes (arrows) within spermatogonia at 18°C in young (B-B′) or aged (E-E′) flies. (C-C′,F-F′) Branched fusomes within spermatogonia next to the hub (arrows) in flies shifted to 29°C for 2 days in young (C-C′) or aged (F-F′) flies. (D-D′) Spectrosomes within revertant GSCs (arrowheads) adjacent to the hub in young flies shifted back to 18°C for 5 days. (G-G′) Spermatogonia that contact the hub contain branched fusomes in testes from aged flies shifted back to 18°C for 5 days. (H) Quantification of testes containing at least one spectrosome in young and aged flies at 18°C (Permissive), 29°C (Restrictive), and recovery at 18°C (Restrictive-Permissive). (I) Average number of GSCs in testes that contained GSCs in young and aged flies raised at 18°C and after the recovery at 18°C. Error bars represent standard error of the mean (SE). Bracket with * shows statistically significant changes, p<0.001 Scale bar: 10 µm. Genotype: Stat92E^F/Stat92E⁰⁶³⁴⁶.