The ubiquitin proteasome system regulates protein expression at the post-translational level by tagging certain proteins with ubiquitin and thereby marking them for degradation by the proteasome complex. This system is highly conserved and is used by almost every eukaryotic cell to degrade and recycle proteins. In this issue (), Margaret Fuller and colleagues uncover a surprisingly specific role for the polyubiquitin Ubi-p63E, encoded by magellan (magn), in the Drosophila spermatogenetic programme. Loss-of-function magn mutants fail to maintain the free ubiquitin pool specifically in the testes, which ultimately results in meiotic arrest and sterility. The authors show that Ubi-p63E is required for normal meiotic chromatin condensation, cell cycle progression and spermatid differentiation, whereas the expression of spermatocyte genes was largely unaffected in the magn mutant. The observed phenotype is likely to be specific to the magn mutant, as knockdown of proteasome subunits had more widespread and severe effects. These data uncover a novel and highly specific mechanism of post-translational regulation via ubiquitin homeostasis in the developing male germline.
