The Origin and Distribution of Cortical Granules in Human Oocytes with Reference to Golgi, Nucleolar, and Microfilament Activitya

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Abstract
The origin and distribution of cortical granules were investigated in human preovulatory oocytes at various phases of maturation. Twenty-five oocytes obtained from unstimulated small antral follicles and from stimulated large antral and mature follicles were examined by transmission electron microscopy. Ovarian stimulation in women was accomplished by administering Clomid followed by hMG or hCG or both. Small antral follicle oocytes were dissected from ovarian biopsies, while the other oocytes were recovered by laparoscopy. Some oocytes were allowed to mature in Ham's F-10 or Whittingham's T-6 media before routine fixation in glutaraldehyde/osmium. Cortical granules originate from typical, hypertrophic Golgi complexes during early maturation and continue till its completion. Evidently there are two waves of cortical granule synthesis, the first more prolific than the second. The first occurred in small antral follicle oocytes, when there was a peak in Golgi activity, and the second was observed at the germinal vesicle stage, particularly at the onset of resumption of meiosis. Golgi complexes became progressively scarce as oocytes completed first maturation. Golgi membranes were also involved in the formation of lysosomes. A well-defined band of microfilaments was detected in small antral follicle oocytes which seemed to prevent the cortical granules, organized in a single layer, from migrating to the periphery. This band gradually became disorganized at the germinal vesicle stage as oocytes resumed meiosis, when cortical granules were apparently migrating to the surface. Metaphase I and mature oocytes had one to three discontinuous layers of cortical granules beneath the oolemma. The general organization of oocytes was also investigated and the roles of the nucleolus and endoplasmic reticulum in relation to Golgi activity and cell secretion were discussed.