Xenopus laevisEgg Jelly Coats Consist of Small Diffusible Proteins Bound to a Complex System of Structurally Stable Networks Composed of High-Molecular-Weight Glycoconjugates

Abstract

The extracellular matrix surroundingXenopus laeviseggs includes three morphologically distinct jelly layers designated J1, J2, and J3 from the innermost to outermost. Previously, using the quick-freeze, deep-etch, rotary-shadow technique, we found that each layer has a unique fibrillogranular ultrastructure. In this study, we show that the fibrillar network is composed of high-molecular-weight glycoconjugates, while the globular material consists of low-molecular-weight proteins some of which are released into the aqueous medium. Analysis by SDS–PAGE and differential staining of individually dissected jelly layers shows that both J1 and J2 contain three high-molecular-weight, acidic, Alcian blue-staining components (450, 630, and 900 kDa), while J3 contains two high-molecular-weight components that stain with PAS but not with Alcian blue. Each jelly layer also contains low-molecular-weight proteins from 75 to 250 kDa that do not stain with PAS or Alcian blue. Chromatography of whole egg jelly on a Sephacryl 500 column resulted in isolation of the major Alcian blue staining band (630 kDa) which eluted first, and two PAS staining bands which eluted second. Rotary-shadowing demonstrated that these high-molecular-weight glycoconjugates are long and branched, suggesting that they are major constituents of the jelly fiber network. SDS–PAGE analysis shows that these networks are stable for at least 16 hr after eggs are oviposited. In contrast, the low-molecular-weight globular proteins which constitute 30% of the total jelly protein are steadily released into the surrounding medium.