Abstract

Advanced maternal age is associated with increased oocyte aneuploidy and early miscarriage. Serum- and glucocorticoid-regulated kinase 1 (SGK1), a member of the serine/threonine kinase family, is downregulated in oocytes from aged mice. However, the mechanisms by which SGK1 controls oocyte maturation remain unclear. Here, we show that SGK1 localizes predominantly to spindle poles during oocyte maturation. Knockdown of SGK1 via siRNA or pharmacological inhibition disrupts spindle assembly and impairs kinetochore-microtubule attachments in mouse oocytes. This disruption leads to sustained activation of the spindle assembly checkpoint, failure of Cyclin B1 and Securin degradation, impaired metaphase I-anaphase transition, and defective first polar body extrusion. Mechanistically, we identify RanBP1 as a potential mediator of SGK1 function during meiotic progression. In porcine oocytes, SGK1 inhibition similarly compromises maturation and Cyclin B1 degradation, suggesting a conserved role across mammalian species. Together, our findings establish SGK1 as a critical regulator of spindle assembly and meiotic progression in mammalian oocytes.