FIG. 3.

Electron micrographs of nuclear envelope exvaginations, their relationship to annulate lamellae and smooth endoplasmic reticulum, and their potential peripheral migration in IV zygotes and two-cell embryos. (A) Low-power micrograph from a porcine zygote showing a site of nuclear envelope exvagination (arrowhead) and apparently detached exvaginations (arrows) in the cytoplasm. (B) Detail from porcine two-cell embryo showing exvagination of the outer membrane of the nuclear envelope. The outer membrane of the nuclear envelope (NE) is continuous with cytoplasmic annulate lamellae (CAL). The dilated perinuclear cisterna contains vesicular structures containing material of varying electron-density (arrowheads). M, mitochondria; SER, smooth endoplasmic reticulum. (C) Apparently detached nuclear envelope exvagination found in the deep cytoplasm in the two-cell embryo. Note the content of vesicular structures containing material of varying electron-density (arrowheads). (D) Apparently detached nuclear envelope exvagination found in the cortical cytoplasm of zygote. Note the intimate spatial relationship between the detached exvagination and the plasma membrane (arrow). For arrowheads, see C. PvS, perivitelline space. (E) Apparently detached nuclear envelope exvagination found in the cortical cytoplasm of the two-cell embryo. Note the continuity between the membrane of the detached exvagination and the smooth endoplasmic reticulum (SER). For arrowheads, see C. M, mitochondria; PvS, perivitelline space.