Abstract. Previously, we showed that the exogenous expression of aquaporin 3 (AQP3), an aquaglyceroporin, improved the tolerance of mouse oocytes to vitrification with a glycerol-based solution. In the present study, we examined conditions suitable for the expression of AQP3 and the ability of vitrified oocytes to develop in vitro and in vivo after fertilization. After only partial remove of cumulus cells, immature mouse oocytes (germinal vesicle stage) were injected with 5, 10 or 20 pg of AQP3 cRNA and cultured for 12 h for maturation. When matured oocytes were vitrified with a glycerol-based solution, 57-61% survived regardless of the amount of cRNA injected (5-20 pg). By contrast, no oocytes injected with water (control) survived. When the zona pellucida was removed from the vitrified oocytes and the oocytes were then fertilized in vitro and cultured, the proportions that were fertilized and developed into blastocysts were higher when the amount of cRNA injected was 5 pg than 10-20 pg. When 16 blastocysts were transferred to a pseudopregnant mouse, 5 developed to term, demonstrating that oocytes vitrified after injection of AQP3 cRNA retained the ability to develop to term. The water-permeability of cRNA-injected oocytes was higher than that of control oocytes from the maturing stage to the 1-cell zygote stage, whereas glycerol-permeability was higher only at metaphase II. This indicates that AQP3 was expressed for a relatively short period of time. These results suggest that the transient expression of water/cryoprotectant channels is effective for cryopreserving cells that have low membrane-permeability, such as mammalian oocytes. Key words: Aquaporin, Development, Membrane-permeability, Oocyte, Vitrification (J. Reprod. Dev. 57: [403][404][405][406][407][408] 2011) he permeability of the plasma membrane to water and cryoprotectants is one of the most important factors for successful cryopreservation of oocytes/embryos because it influences the formation of intracellular ice, the toxicity of cryoprotectants and osmotic swelling [1]. For cryopreservation of oocytes/embryos, vitrification has advantages over slow freezing in terms of the simplicity of the method and viability of the cells. As the solution used for vitrification contains a high concentration of cryoprotectants, it is much more toxic than the solution for slow-freezing. Therefore, the permeability of the plasma membrane would affect the survival of cryopreserved cells more in vitrification than in slow freezing. If the permeability is low, insufficient exposure to the cryoprotectants causes formation of intracellular ice. However, excessive exposure results in toxic effects of the cryoprotectants. Therefore, high permeability to water and cryoprotectants would be preferable for vitrification.We showed that a simple one-step method is effective for vitrification of mouse morulae [2] but that a two-step method with a pretreatment with a lower concentration of the cryoprotectant is favorable for vitrifying mouse embryos at early cleavage stages...