The hyaline layer in early development of the sea urchin: Cell-extracellular matrix interactions

Abstract

The hyaline layer is released by the sea urchin zygote starting about 30 seconds after fertilization. This layer is elevated above the surface of the zygote where it serves as a protective layer, a barrier to polyspermy, and as an adhesive substrate for the early stages of development. We have been interested in learning how the hyaline layer is stored in the egg, how it is released after fertilization, and how it functions as an extracellular matrix during early development. The layer contains about fifteen abundant proteins plus a number of others that may be present or may contaminate preparations of the layer during isolation procedures. Our goal was to identify the major components of the hyaline membrane, to follow assembly of the structure after fertilization, and to identify molecules that are active as adhesive substrates for cells.Using double-label immunofluorescence and ultrastructural immunogold localization of polyclonal and monoclonal antibodies, the components of the hyaline layer have been localized to four vesicle classes in the unfertilized egg. Centrifugation studies on unfertilized eggs and double-label immunofluorescent studies have shown that the four classes each contain a distinct group of proteins. The four vesicles were followed through oogenesis to learn when proteins of each class were synthesized by the oocyte. Each of the four classes (cortical granules, basal lamina vesicles, apical vesicles and echinonectin vesicles) were synthesized, localized, and relocalized in the oocyte by unique spatial and temporal pathways.