Figure 2. Knockdown of gfzf^sim rescues cell proliferation defects and restores hybrid male viability.

a) No hybrid males are recovered in crosses where the pValium20- gfzf^sim RNAi construct is not expressed (no GAL4 driver, “RNAi OFF”). In crosses between D. simulans males and D. melanogaster females carrying one copy each of pValium20- gfzf^sim and a ubiquitously expressing Actin5C-GAL4 driver, one out of four possible hybrid male progeny inherit both pValium20- gfzf^sim and the Actin5C-GAL4 driver (“RNAi ON”) and produce viable F1 hybrid male progeny. P values were calculated using Fisher’s exact test. b) RNAi knockdown of gfzf^sim by a T80-GAL4 driver, more specific to larval neuroblasts and imaginal discs, successfully restores the viability of F1 male hybrids. c) EdU staining shows the diminutive larval brains and cell proliferation defects in ‘inviable’ hybrid males compared to viable F1 hybrid female larvae. These cell proliferation defects are also partially rescued in hybrid males upon gfzf^sim knockdown.