Cyst stem cell lineage GAL4 transgenes are robustly expressed in hub cells of the Drosophila testis stem cell niche.

Manipulating gene expression in the different cell types of the Drosophila melanogaster testis stem cell niche is critical to understanding its biology. Here, we tested the specificity of commonly used somatic cyst stem cell (CySC) lineage GAL4 drivers by assessing their abilities to promote loss of hub cell quiescence. We found that conditional reduction of the cell cycle inhibitor Retinoblastoma (Rbf) using c587-GAL4 , tj-GAL4 , eyaA3-GAL4 , or zfh1-GAL4 is sufficient to drive quiescent hub cells into mitosis, with increased penetrance at higher temperature due to higher GAL4 activity. Concomitant inhibition of GAL4 expression in hub cells via hh-GAL80 eliminates hub cell proliferation, supporting that hub cells autonomously require Rbf to maintain quiescence. Thus, the activity of GAL4 drivers commonly used to manipulate the CySC lineage also functionally affect hub cells.