A new technique for isolation and visualization of the Xenopus egg cortex reveals a complex cytoskeleton

This paper demonstrates the first images of the isolated cortex of the Xenopus laevis egg viewed as a whole mount. The cortex was isolated by mechanically restraining it in a folding hexagonal mesh electron microscopy grid, dried by passage through the carbon dioxide critical point, and viewed in an intermediate voltage electron microscope at 400 kV. Using this approach, we have obtained new views of the Xenopus egg cortex that demonstrate a complex cytoskeleton. Stereo micrographs demonstrate three-dimensional views of the cortical organelles and their interaction with the cytoskeleton. These images demonstrate the presence of a dense meshwork of filaments located just beneath the plasma membrane, referred to as the submembranous cytoskeleton. In addition, there is an array of filaments interconnecting the organelles and securing them to the submembranous cytoskeleton and plasma membrane. The development of this technique for visualization of the egg cortex will facilitate further analysis of the role of the cortical cytoskeleton in fertilization and early embryogenesis.