Received March 03, 2017
Accepted August 17, 2017

Objective: Oocyte-sperm interaction is the essential step for fertilization. Juno, which has been known to Folate receptor 4, is the Izumo1 receptor expressed on oocyte membrane. This study aims to investigate the localization and expression of Juno in mice oocytes during maturation. Methods: To confirm the stage at which Juno expression begins in the mice oocytes and its localization pattern, we performed immunostaining methods. Next, we evaluated the Juno mRNA expression by a half quantitative RT-PCR. Juno knockdown oocytes were generated by microinjecting siRNA into the germinal vesicle (GV) stage oocytes, and analyzed the maturation rate. Results: Our results shown that Juno was expressed on the surface of cytoplasmic membrane of oocytes at GV stage and it continues to be expressed at similar levels in metaphase II (MII) stages of oocytes maturation. Interestingly, Juno is also expressed on the first polar body membrane at MII stage. Fluorescence showing the expression of Juno was decreased in the oolemma of siRNA injected oocytes, but it was not completely disappears in knock down oocytes. MII stage-rates of siRNA injected oocytes were not significantly different from sham controls. Conclusion: Juno was expressed in oocytes at the GV stage and it continues to be expressed at similar levels in later stages of oocytes maturation. Juno accumulation in oolemma during oocyte maturation is essential for fertilization, such as membrane recognition of both gametes.