Ultrastructure of human oocytes of different maturity stages and the alteration during in vitro maturation  Yong-jie Yang, M.Sc., Yan-jun Zhang, Ph.D., Yuan Li, Ph.D., M.D.  Fertility and Sterility  Volume 92, Issue 1, Pages 396.e1-396.e6 (July 2009) DOI: 10.1016/j.fertnstert.2009.02.010 Copyright © 2009 American Society for Reproductive Medicine Terms and Conditions

Figure 1 Ultrastructure of human oocytes of different maturity stages during in vitro maturation. (A) Electron micrograph of oocytes at GV stage showing rare and small microvilli, and a zona pellucida with loose outside and tight inside. Bar = 1μm. (B) Electron micrograph of in vitro cultured immature oocytes at MI stage after GVBD, showing larger microvilli in both number and size; mitochondria can be seen coming along with lipid droplets. Bar = 1μm. (C) Electron micrograph of the microvilli of immature oocytes at MI stage after GVBD, showing gap junctions (↑) between the GCs and microvilli of the oocyte. Bar=0 .1μm. (D) Electron micrograph of in vitro cultured mature oocytes, demonstrating withdrawn microvilli. Bar=1μm. (E) Electron micrograph of mature oocytes with its first polar body. Cortical granules are distributed beneath the membrane in a symmetrical manner. Bar=1μm. (F) Electron micrograph of oocytes at GV stage, showing vesicle-like Golgi apparatus. Bar=0.1μm. (G) Electron micrograph of oocytes at GV stage, showing cortical granules accompanied by mitochondria. Bar=0.1μm. (H) Electron micrograph of oocytes at MII stage, demonstrating mitochondrial degeneration with reduced cristae. Bar=0.1μm. (I). Light micrograph of oocytes at GV stage, showing the nucleus and dense nucleolus. Bar=10μm. (J) Electron micrograph of immature oocytes at MI stage after GVBD, showing the desmosome (↑) between granulosa cells. Bar=0.1μm. (K) Electron micrograph of immature oocytes at MI stage after GVBD, showing the tight junction (↑) between granulosa cells. Bar=0.1μm. (L) Electron micrograph of cumulus granulosa cell apoptosis, showing the corrugated nuclear envelope and dense chromatin. Bar=1 μm. (M). Electron micrograph of cumulus granulosa cell apoptosis, showing the apoptotic body with nuclear fragmentation (↑). Bar=1μm. (N) Electron micrograph of oocyte with poor evaluation, showing swollen mitochondria, with blurred cristae and membrane. Bar=0.1μm. (O) Electron micrograph of oocyte with poor evaluation, showing a fractured first polar body. Bar=1μm. Mv = microvilli; ZP = zona pellucida, CG, cortical granules; Mi, mitochondria; L, lipid droplets, FPB, first polar body; RER, rough endoplasmic reticulum; Go, Golgi apparatus, SER, smooth endoplasmic reticulum, N, nucleus. Fertility and Sterility 2009 92, 396.e1-396.e6DOI: (10.1016/j.fertnstert.2009.02.010) Copyright © 2009 American Society for Reproductive Medicine Terms and Conditions