Testes of homozygous Rexo5^c04255 second instar male larvae are much smaller in size compared to age-matched controls and their gonioblast divisions are arrested at the first or second mitotic division, assed by the level of fusome branching.

Rexo5^c04255 mutants are rescued to adulthood by Scer\GAL4^Act.PU-driven expression of Rexo5^Scer\UAS, yet (due to poor expression in germline) the males display defects in differentiation of the spermatogonial cells as well as distribution of multicellular germ cell cysts that are now present throughout the testicular tube (rather than being restricted to the apical tip as in wild-type); no meiotic nuclei are detected in the mutant germ cells at day 3 post-eclosion. The rescued females are sterile with only rudimentarily developed small ovaries (reminiscent of the string-of-pearls phenotype), the oocytes do not fully develop and display egg-chamber degeneration at stages 4-6. Near complete loss of germline stem cells and germarium proliferation defects are observed at 14 days post-eclosion.