Drosophila S6 Kinase: A Regulator of Cell Size

Cell proliferation requires cell growth; that is, cells only divide after they reach a critical size. However, the mechanisms by which cells grow and maintain their appropriate size have remained elusive. Drosophila deficient in the S6 kinase gene ( dS6K ) exhibited an extreme delay in development and a severe reduction in body size. These flies had smaller cells rather than fewer cells. The effect was cell-autonomous, displayed throughout larval development, and distinct from that of ribosomal protein mutants ( Minutes ). Thus, the dS6K gene product regulates cell size in a cell-autonomous manner without impinging on cell number.