A spiral array of microtubules in the fertilized sea urchin egg cortex examined by indirect immunofluorescence and electron microscopy

Abstract

A transient spiral system of fibers in the cortex of fertilized eggs of the sea urchin Strongylocentrotus purpuratus was examined with indirect immunofluorescence microscopy and found to contain tubulin. Electron microscopy identified the tubulin-containing bands as bundles of up to 40 or more microtubules. These cortical microtubules, which are initially radial, form a spiral array about the time of pronuclear fusion. This basket-like structure, at a depth of 10–15 μm below the cell surface, reaches a peak of development about 45 min after fertilization and disappears before the streak stage at 70 min, in a division cycle of slightly more than 2 h. Possible functions of the cortical microtubules, which appear to be independent of the interphase asters, are discussed.