Sloan-Kettering virus gene product of a cellular protooncogene c-Ski is an unique nuclear pro-oncoprotein and belongs to the Ski/Sno proto-oncogene family. Ski plays multiple roles in a variety of cell types, it can induce both oncogenic transformation and terminal muscle differentiation when expressed at high levels. The aim of the present study was to locate Ski protein in rat ovaries in order to predict the possible involvement of Ski in follicular development and atresia. First, expression of c-Ski mRNA in the ovaries of adult female rats was confirmed by RT-PCR. Then, ovaries obtained on the day of estrus were subjected to immunohistochemical analysis for Ski and proliferating cell nuclear antigen (PCNA) in combination with terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL). Ski was expressed in granulosa cells that were positive for TUNEL, but negative for PCNA, regardless of the shape and size of follicles. Expression of Ski in TUNEL-positive granulosa cells, but not in PCNA-positive granulosa cells, was also verified in immature hypophysectomized rats having a single generation of developing and atretic follicles by treatment with equine chorionic gonadotropin (eCG). These results indicate that Ski is profoundly expressed in the granulosa cells of atretic follicles, but not in growing follicles, and suggest that Ski plays a role in apoptosis of granulosa cells during follicular atresia.

ABSTRACT   INTRODUCTION   MATERIALS AND METHODS    Animals    Animal Models    Extraction of Total RNA    Reverse Transcription-Polymerase Chain Reaction (RTPCR)    Determination of Apoptotic Cells by TUNEL Method   RESULTS    Expression of c-Ski Gene in Various Tissues    Localization of Ski Protein in the Follicles of Adult Female Rats    Ski Protein Expression in Granulosa Cells of Atretic Follicles    Localization of Ski Protein in the Follicles of Single Generation in eCG-Primed Immature Hypophysectomized Rats   DISCUSSION   REFERENCES

• Hyun Kim(Department of Veterinary Physiology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Animal Genetic Resources Station, National Institute of Animal Science, RDA) Corresponding author
• Takashi Matsuwaki(Department of Veterinary Physiology, Graduate School of Agricultural and Life Sciences, The University of Tokyo)
• Keitaro Yamanouchi(Department of Veterinary Physiology, Graduate School of Agricultural and Life Sciences, The University of Tokyo)
• Masugi Nishihara(Department of Veterinary Physiology, Graduate School of Agricultural and Life Sciences, The University of Tokyo)
• Sungwoo Kim(Animal Genetic Resources Station, National Institute of Animal Science, RDA)
• Yeoung-Gyu Ko(Animal Genetic Resources Station, National Institute of Animal Science, RDA)
• Boh-Suk Yang(Animal Genetic Resources Station, National Institute of Animal Science, RDA)