Gamete Biology

Localization of Mitotic Arrest Deficient 1 (MAD1) in Mouse Oocytes During the First Meiosis and Its Functions as a Spindle Checkpoint Protein

Abstract
The present study was designed to investigate the localization of mitotic arrest deficient 1 (MAD1) in mouse oocytes during meiotic maturation and its relationship with kinetochores, chromosomes and microtubules. Oocytes at various stages during the first meiosis were fixed and immunostained for MAD1, kinetochores, microtubules and chromosomes. The stained oocytes were examined by confocal microscopy. Some oocytes were treated with nocodazole or Taxol before examination. Anti-MAD1 antibody was injected into the oocytes at germinal vesicle (GV) stage for examination of chromosome alignment and spindle formation. It was found that MAD1 was present in the oocytes from GV to prometaphase I (ProM-I) stages around the nuclei. When the oocytes reached metaphase I (M-I) to metaphase II (M-II) stages, MAD1 was mainly localized at the spindle poles. MAD1 relocated to the vicinity of the chromosomes when spindles were disassembled by nocodazole or cooling and the relocated MAD1 moved back to the spindle poles during spindle recovery. Taxol treatment did not affect the MAD1 localization. Although anti-MAD1 antibody injection did not affect nuclear maturation, significantly higher proportions of injected oocytes had misaligned chromosomes when the oocytes reached M-I to M-II stages. The present study indicates that MAD1 is present in mouse oocytes at all stages during the first meiosis and it participates in spindle checkpoint during meiosis. However, MAD1 could not check misaligned chromosomes during spindle recovery after the spindles were destroyed by drug or cooling, which caused some chromosomes to scatter in the oocytes.

Key words: Gamete Biology • Meiosis • Oocyte development

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