Abstract
Sirtuins play an important role in female mammalian reproductive function, participating in folliculogenesis and oocyte maturation. Studies exploring the consequences of inhibition/deletion of a specific sirtuin (SIRT) have demonstrated a deleterious effect on follicular growth, oocyte maturation, fertilization rates and embryo development, suggesting that sirtuins must have a relevant role in these processes. However, the exact mechanisms behind sirtuin function are still unclear. Most of the knowledge currently available derives from mouse studies and the literature is scarce in other species. So far, there is insufficient information about the subcellular localization of sirtuins during bovine meiosis, which would contribute to understanding the role and participation of sirtuins in the process of oocyte maturation, due to the close relation between location and function. Using in vitro maturation (IVM) of bovine oocytes we comprehensively documented and illustrated the subcellular localization pattern and distribution of SIRT1, 2 and 3 during meiotic progression. Moreover, we also detailed and quantified the colocalization of those sirtuins with the meiotic spindle, from the germinal-vesicle (GV)-stage until the Metaphase-II (MII)-stage. Our study demonstrated an increase in the expression of SIRT1, 2 and 3 during in vitro oocyte maturation and, for the first time, colocalization of SIRT1, 2 and 3 with both metaphase-I and metaphase-II spindles. These findings suggest that all three sirtuins may have a role in meiotic spindle assembly and microtubule dynamics in the bovine model. In addition, we have demonstrated the nuclear presence of SIRT1 and SIRT2 in the GV-stage. The apparent perinucleolar location of SIRT2 suggests that SIRT2 may shuttle into the nucleus at the GV-stage to regulate heterochromatin. This study reinforces the value of sirtuins during in vitro bovine meiotic progression and indicates potential molecular targets to improve maturation rates and embryo development.