Translational control is crucial for the correct timing of developmental events such as spermatogenesis that take place in the absence of transcription. In this issue of Development, two papers describe the role of eIF4G2 - a novel orthologue of eukaryotic initiation factor 4G (eIF4G)- in translational control of spermatogenesis in Drosophila. eIF4G acts as a scaffold protein in the eIF4F translation initiation complex. On ,Franklin-Dumont et al. report that eIF4G2, which they call Off-schedule (Ofs),couples translational control to meiosis and differentiation during spermatogenesis. They show that, during the meiotic G2 phase of spermatogenesis, ofs mutant germ cells do not reach their correct size and fail to undergo meiosis or differentiate significantly. Furthermore,they report, the accumulation of four cell cycle regulators (Cyclin A, Boule,Twine and Roughex) is altered. They also show that Ofs has eIF4G activity and suggest that it substitutes for this protein in spermatocytes. Given these results, Franklin-Dumont and colleagues speculate that spermatocytes must accumulate sufficient cell mass (a process that requires active translation)before they can execute meiosis and differentiation, and that a checkpoint stops these processes if the spermatocytes have not grown enough. On , Baker and Fuller also provide evidence that translational control regulates meiosis and differentiation in Drosophila spermatocytes. They report that flies mutant for eIF4G2 are viable but that the males are sterile. They then show that, although spermatocytes form in the mutant flies, the germ cells skip the major events of the meiotic divisions. eIF4G2 function, they report, is needed for the normal accumulation of the core cell cycle regulators Twine and Cyclin B in mature spermatocytes; loss of eIF4G2 function also causes widespread defects in spermatid differentiation, including a failure to elongate properly. Thus, suggest Baker and Fuller, a specialized form of the translation initiation machinery is required for the regulation and execution of key steps in male germ cell differentiation. Together, these two papers thus provide important new insights into how translational control ensures that the meiotic cell cycle is coordinated with differentiation during spermatogenesis to produce viable spermatozoa.
