Collection and preparation of ovarian tissue
Ovarian tissue samples were harvested following the method of Kim et al. (2012). Ovaries of five normal Landrace pigs (age: 10 months, weight: 110 ± 5.1 kg; Farm Animal, Ansung, Korea) and five miniature pigs (age: 10 months, weight: 26 ± 2.1 kg; Medi Kinetics Co., Ltd. Pyeongtaek, Korea) were collected on day 15 of the oestrous cycle from a local slaughterhouse at Pyeong-Nong, Pyeongtaek, Korea. The samples were placed into a freezer box in liquid N2 and transported to the laboratory within 2 h. Follicles at different developmental stages were separated and designated as developing, Graafian, and ovulated follicles according to the standards described by Stocco et al. (2007). Experiments were conducted in strict compliance with the recommendations specified in the Guide for the Care and Use of Laboratory Animals issued by the National Institutes of Health. The protocol was approved by the Committee on the Ethics of Animal Experiments of Hankyong National University (Permit Number: 2013-1).