English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

Eggs of the sea urchin Strongylocentrotus purpuratus were quick-frozen, freeze fractured, and deep-etched to reveal the detailed structure of the vitelline layer (VL), an extracellular coat. The VL consisted of a network of fibers lying in sheet raised 20 nm off the plasma membrane and connected to it by a series of short processes. Sperm attached to the fibers of this sheet and upon fertilization the VL rose off the egg surface to form the fertilization envelope (FE). By 1 min postinsemination (p.i.), the FE had become augmented by a new set of smaller fibrils, and the original fibers of the VL appeared to be undergoing degradation. The FE exhibited casts of microvilli the VL had once covered. These were rounded at 1 min p.i., but by 2 min they had become angular and coated with an orderly array of repeating macromolecular units. In areas between casts, the coating process was slower; incomplete rows of units were seen at 5 min p.i. and complete rows at 10 min. Deep-etching of FE isolated from eggs by homogenization and differential centrifugation showed that both top and bottom surfaces were coated. The coat pattern was made up of 17.5-nm wide rows of parallelogram-like units that repeated every 12.2 nm along the row axis. Units in adjacent rows were in register to produce a secondary axis 76 degrees from the row axis. The results of this and previous studies suggest that the coating process plays a major role in "hardening" the FE to produce a tough barrier that protects the early embryo from chemical and mechanical injury.

The vitelline layer of the sea urchin egg and its modification during fertilization. A freeze-fracture study using quick-freezing and deep-etching.