Sirtuin proteins are evolutionary conserved Sir2-related NAD+-dependent deacetylases and regulate many of cellular processes such as metabolism, inflammation, transcription, and aging. Sirtuin contains activity of either ADP-ribosyl-transferase or deacetyltranfease and their activity is dependent on the localization in cells. However, the expression pattern of Sirtuins has not been well studied. To examine the expression levels of Sirtuins, RT-PCR was performed using total RNAs from various tissues including liver, small intestine, heart, brain, kidney, lung, spleen, stomach, uterus, ovary, and testis. Sirtuins were highly expressed in most of tissues including the testis. Immunostaining assay showed that Sirt1 and Sirt6 were mainly located in the nucleus of germ cells, spermatocytes, and spermatids in the seminiferous tubules, whereas Sirt2 and Sirt5 were exclusively present in the cytoplasm of germ cells and sperma-tocytes. Our results indicate that Sirtuins may function as regulators of spermatogenesis and their activities might be dependent on their location in the seminiferous tubules.

Primary oocytes that are arrested in first meiotic prophase for years enter maturation process to meet a critical precondition for successful fertilization. During maturation, oocyte finishes meiosis I and progresses to the metaphase II stage, achieving meiotic maturity. Although importance of oocyte maturation for oocyte quality has been recognized, it is not fully understood for molecular mechanisms underlying oocyte maturation. Here, we found that dexamethasone-induced Ras-related protein 1 (RASD1), a member of RAS superfamily of small GTPases, was expressed in the mouse ovary. Immunohistochemical analysis revealed that Rasd1 expression was dominant in oocyte cytoplasm. Real-time PCR and RT-PCR analyses showed that Rasd1 mRNA was steadily expressed in germinal vesicle (GV), germinal vesicle break down (GVBD), metaphase I (MI) oocytes, but decreased in metaphase II(MII) oocytes during oocyte maturation. Konckdown of Rasd1 using RNAi system in the GV oocytes suppressed oocyte maturation through disruption of meiotic spindle and formation of misarranged chromosomes. Taken together, Rasd1 is a critical factor for MI-MII transition of oocyte and is involved in the regulation of spindle formation during oocyte maturation. Further study is needed to examine relationship between Rasd1 and spindle formation in MI-MII transition.