The role of RING box protein 1 in mouse oocyte meiotic maturation.

RING box protein-1 (RBX1) is an essential component of Skp1-cullin-F-box protein (SCF) E3 ubiquitin ligase and participates in diverse cellular processes by targeting various substrates for degradation. However, the physiological function of RBX1 in mouse oocyte maturation remains unknown. Here, we examined the expression, localization and function of RBX1 during mouse oocyte meiotic maturation. Immunofluorescence analysis showed that RBX1 displayed dynamic distribution during the maturation process: it localized around and migrated along with the spindle and condensed chromosomes. Rbx1 knockdown with the appropriate siRNAs led to a decreased rate of first polar body extrusion and most oocytes were arrested at metaphase I. Moreover, downregulation of Rbx1 caused accumulation of Emi1, an inhibitor of the anaphase-promoting complex/cyclosome (APC/C), which is required for mouse meiotic maturation. In addition, we found apparently increased expression of the homologue disjunction-associated protein securin and cyclin B1, which are substrates of APC/C E3 ligase and need to be degraded for meiotic progression. These results indicate the essential role of the SCF(βTrCP)-EMI1-APC/C axis in mouse oocyte meiotic maturation. In conclusion, we provide evidence for the indispensable role of RBX1 in mouse oocyte meiotic maturation.