Reorganization of the Endoplasmic Reticulum and Development of Ca²⁺ Release Mechanisms During Meiotic Maturation of Human Oocytes

Oocyte maturation in rodents is characterized by a dramatic reorganization of the endoplasmic reticulum (ER) and an increase in the ability of an oocyte to release Ca²⁺ in response to fertilization or inositol 1,4,5-trisphosphate (IP₃). We examined if human oocytes undergo similar changes during cyt...

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Bibliographic Details
Published in:Biology of reproduction 2010-10, Vol.83 (4), p.578-583
Main Authors: Mann, Jessica S, Lowther, Katie M, Mehlmann, Lisa M
Format: Article
Language:English
Subjects:
Adult
Animals
Biological and medical sciences
Blotting, Western
Calcium - physiology
Cell Polarity - physiology
Endoplasmic Reticulum - physiology
Endoplasmic Reticulum - ultrastructure
Female
Fundamental and applied biological sciences. Psychology
Humans
Inositol 1,4,5-Trisphosphate - pharmacology
Inositol 1,4,5-Trisphosphate Receptors - physiology
Meiosis - physiology
Mice
Microscopy, Confocal
Oocytes - physiology
Oocytes - ultrastructure
Vertebrates: reproduction
Young Adult
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Summary:Oocyte maturation in rodents is characterized by a dramatic reorganization of the endoplasmic reticulum (ER) and an increase in the ability of an oocyte to release Ca²⁺ in response to fertilization or inositol 1,4,5-trisphosphate (IP₃). We examined if human oocytes undergo similar changes during cytoplasmic meiotic maturation both in vivo and in vitro. Immature, germinal vesicle (GV)-stage oocytes had a fine network of ER throughout the cortex and interior, whereas the ER in the in vivo-matured, metaphase II oocytes was organized in large (diameter, ~2-3 μm) accumulations throughout the cortex and interior. Likewise, oocytes matured in vitro exhibited cortical and interior clusters with no apparent polarity in regard to the meiotic spindle. In vivo-matured oocytes contained approximately 1.5-fold the amount of IP₃ receptor protein and released significantly more Ca²⁺ in response to IP₃ compared with GV-stage oocytes; however, oocytes matured in vitro did not contain more IP₃ receptor protein or release more Ca²⁺ in response to IP₃ compared with GV-stage oocytes. These results show that at least one cytoplasmic change occurs during in vitro maturation of human oocytes that might be important for fertilization and subsequent embryonic development, but they suggest that a low developmental competence of in vitro-matured oocytes could be the result of deficiencies in the ability to release Ca²⁺ at fertilization.
ISSN:0006-3363
1529-7268
DOI:10.1095/biolreprod.110.085985