Fig. 8. A current working model for how Bmp signals maintain GSCs in the Drosophila testis. In this model, Upd from hub cells, Gbb/Dpp from hub cells/somatic stem cells are important for GSC maintenance. An unknown signal initiated by EGFR/Raf signaling from somatic cyst cells is important for the proper differentiation of gonialblasts. Dpp/Gbb signaling also helps repress bam expression in GSCs and in gonialblasts (GBs). Two-cell germ cell clusters distant from hub cells/somatic stem cells receive less Bmp signaling and begin to express bam and promote further differentiation.