A Freeze‐Fracture Study of the Cortex of Xenopus laevis Eggs

The organization of the cortex of Xenopus laevis eggs was investigated by freeze‐fracture electron microscopy. The cortical endoplasmic reticulum (CER) formed a network surrounding and interconnecting the cortical granules. It formed junctions with the plasma membrane and was confluent with the ER in subcortical regions. Intramembranous particles (IMP1) were only present in the P face of the CER, the E face being apparently devoid of pits and particles. Arrays of densely packed IMP1, having a mean diameter of 17 nm, were restricted to the microvillar region of the plasma membrane. The cortical granule membrane also contained IMP1 (mean diameter, 21 nm) that were sparsely and randomly distributed. Several types of cortical granule seemed to exist based on an analysis of the distribution of the different IMP sizes.