THE SEA-URCHIN EGG JELLY COAT IS A 3-DIMENSIONAL FIBROUS NETWORK AS SEEN BY INTERMEDIATE VOLTAGE ELECTRON-MICROSCOPY AND DEEP-ETCHING ANALYSIS

The egg jelly (EJ) coat which surrounds the unfertilized sea urchin eg g undergoes extensive swelling upon contact with sea water, forming a three-dimensional network of interconnected fibers extending nearly 50 mum from the egg surface. Owing to its solubility, this coat has been difficult to visualize by light and electron microscopy. However, Lyt echinus pictus EJ coats remain intact, if the fixation medium is maint ained at pH 9. The addition of alcian blue during the final dehydratio n step of sample preparation stains the EJ for visualization of resin embedded eggs by both light and electron microscopy. Stereo pairs take n of thick sections prepared for intermediate voltage electron microsc opy (IVEM) produce a three-dimensional image of the EJ network, consis ting of interconnected fibers decorated along their length by globular jelly components. Using scanning electron microscopy (SEM), we have s hown that before swelling, EJ exists in a tightly bound network of jel ly fibers, 50-60 nm in diameter. In contrast, swollen EJ consists of a greatly extended network whose fibrous components measure 10 to 30 nm in diameter. High resolution stereo images of hydrated jelly produced by the quick-freeze/deep-etch/rotary-shadowing technique (QF/DE/RS) s how nearly identical EJ networks, suggesting that dehydration does not markedly alter the structure of this extracellular matrix.