The first polar body does not predict accurately the location of the metaphase II meiotic spindle in mammalian oocytes

Objective: To evaluate how well polar body location predicts spindle localization and to examine spindle morphology. Design: Randomized, controlled animal study. Setting: University-affiliate research laboratory. Animal(s): Mature, female golden hamsters. Intervention(s): After superovulation with pregnant mare serum gonadotropin and hCG, metaphase II oocytes were obtained and imaged under digital polarization microscopy. Main Outcome Measure(s): Identify the meiotic spindle in living, unfixed hamster oocytes and determine spindle location relative to the polar body. Result(s): Spindles were imaged in 30 oocytes and only in 5 of them could the polar body predict the spindle localization. In the remaining oocytes, the spindles presented a random distribution within the cytoplasm. Conclusion(s): These data show that the polar body location is not an accurate predictor for meiotic spindle location in mammalian oocytes.