A transgene expressing nuclear GFP under the control of the Tret1 enhancer (Hertenstein et al., 2021) showed GFP expression in the testis, specifically in hub cells and in Eya-positive differentiating cyst cells (Fig. 1C), but was absent from Zfh1-positive CySCs and Vasa-positive germ cells. The gene discussed is DDX4; the disease is cyst.