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. Author manuscript; available in PMC: 2021 Aug 31.
Published in final edited form as: Dev Cell. 2021 Aug 6;56(16):2284–2294.e6. doi: 10.1016/j.devcel.2021.07.010

Figure 6: Model of the communication between CySCs and hub cells that underlies hub cell maintenance.

Figure 6:

(A) In a young wild type testis, hub cells are quiescent. (1) Fs is produced by CySCs downstream of Dp/E2f1 either directly or indirectly. (2) Daw is produced by hub cells and CySCs. Daw is inactivated by Fs and does not activate its receptor Babo on hub cells. (3) In quiescent hub cells, Activin signaling is not activated.

(B) In an old testis or a testis lacking CySCs, (1) Fs expression declines while increased Daw can now activate Babo on hub cells. (2) Activin signaling disrupts hub cell quiescence, leading to hub-to-CySC transdifferentiation.