• 最初集中在前期核周圍的細胞器重新定位到外圍並均勻分佈在整個卵質中。
• 隨著成熟的進行，不同的分泌裝置似乎轉變為聚集在卵母細胞表面下方的皮質顆粒。
• 內質網可變元件和多個線粒體組成的具有原始形態的異源複合物逐漸形成。
• 在 GV 卵母細胞中，胞器在整個細胞質中表現出非均勻分佈。
• 亞細胞結構集中在核週區域，而油質下方的細胞質似乎缺乏細胞器。
• 在紡錘體陽性的 MI 和 MII 卵母細胞中，除減數分裂紡錘體區域外，細胞器均勻地分散在整個細胞體積中。
• GV 卵母細胞非常大的前期核（直徑 29μm）含有緻密的電子緻密核仁和相關的染色質質量，顯示出不同程度的濃縮。
• 在 MI 和 MII 卵母細胞中，在卵母細胞附近檢測到減數分裂紡錘體。
• 人類卵母細胞減數分裂紡錘體是在沒有典型中心體的情況下組裝的
• 所有成熟階段的卵母細胞中最豐富的細胞器是線粒體。
• 線粒體的形態及其數量在減數分裂成熟過程中似乎沒有顯著變化。
• 線粒體群與 ER 形成特徵複合物，作為細胞內鈣 (Ca2+) 的主要儲存庫

https://academic.oup.com/biolreprod/article/104/1/106/5909494?login=false

Cytoplasmic maturation in human oocytes: an ultrastructural study † 

Female fertility relies on successful egg development. Besides chromosome segregation, complex structural and biochemical changes in the cytoplasmic compartment are necessary to confer the female gamete the capacity to undergo normal fertilization and sustain embryonic development. Despite the profound impact on egg quality, morphological bases of cytoplasmic maturation remain largely unknown. Here, we report our findings from the ultrastructural analysis of 69 unfertilized human oocytes from 34 young and healthy egg donors. By comparison of samples fixed at three consecutive developmental stages, we explored how ooplasmic architecture changes during meiotic maturation in vitro. The morphometric image analysis supported observation that the major reorganization of cytoplasm occurs before polar body extrusion. The organelles initially concentrated around prophase nucleus were repositioned toward the periphery and evenly distributed throughout the ooplasm. As maturation progressed, distinct secretory apparatus appeared to transform into cortical granules that clustered underneath the oocyte's surface. The most prominent feature was the gradual formation of heterologous complexes composed of variable elements of endoplasmic reticulum and multiple mitochondria with primitive morphology. Based on the generated image dataset, we proposed a morphological map of cytoplasmic maturation, which may serve as a reference for future comparative studies. In conclusion, this work improves our understanding of human oocyte morphology, cytoplasmic maturation, and intracellular factors defining human egg quality. Although this analysis involved spare oocytes completing development in vitro, it provides essential insight into the enigmatic process by which human egg progenitors prepare for fertilization.

• The organelles initially concentrated around prophase nucleus were repositioned toward the periphery and evenly distributed throughout the ooplasm.
• . As maturation progressed, distinct secretory apparatus appeared to transform into cortical granules that clustered underneath the oocyte's surface.
• The gradual formation of heterologous complexes composed of variable elements of endoplasmic reticulum and multiple mitochondria with primitive morphology. 
• In all GV oocytes, detectable organelles displayed non-homogenous distribution throughout the cytoplasm. 
• The subcellular structures were concentrated in the perinuclear region, whereas the cytoplasm underneath the oolema appeared to be devoid of organelles.
• in spindle-positive MI and MII oocytes, the organelles were dispersed homogeneously throughout the entire volume of the cell except in the meiotic spindle territory. 
• The remarkably large prophase nuclei of GV oocytes (29.06 ± 1.63 μm in diameter) were found to contain compact electron-dense nucleoli and an associated mass of chromatin showing different degrees of condensation.
• In MI and MII oocytes, the meiotic spindle was detected close to the oolema. 
• In human oocytes, the meiotic spindle is assembled in the absence of typical centrosomes 
• 
  
• The cytoplasmic organelles detectable in our samples were mainly represented by mitochondria, endoplasmic reticulum (ER), and Golgi apparatus (GA). 
• The most abundant organelles in oocytes of all maturational stages were the mitochondria. 
• The morphology of the mitochondria, as well as their number, did not seem to change dramatically during meiotic maturation.
• The mitochondrial population formed characteristic complexes with ER, which serves as the primary storage for intracellular calcium (Ca2+) 
• Our observations raise questions regarding the functional significance of organelle rearrangements in preparation for fertilization and the morphological factors defining the quality of the human egg.

The morphometric analysis of organelle distribution in the cytoplasmic compartment of maturing human oocytes. The organelle density in the periphery versus central area of individual cells was compared (A), the average ratio was calculated in individual GV, MI, and MII oocytes and plotted for developmental categories (B). The number of analyzed oocytes is stated in brackets. *p-value ˂ 0.001.

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