Polypeptide composition and organization of the sea urchin extraembryonic hyaline layer.  The protein composition and organization of the sea urchin extraembryonic hyaline layer was examined. Hyalin and a polypeptide of 45 kilodaltons (kDa) were present in hyaline layers isolated from 1-h-old embryos through to the pluteus larva stage. In contrast, several polypeptide species ranging in size from 175 to 32 kDa either decreased in amount or disappeared from the layer as embryonic development proceeded. Concomitant with the changes in composition, hyaline layers became progressively more refractory to dissolution by washing in Ca2+, Mg2(+)-free seawater. Incubation of intact layers, isolated from 1-h-old embryos, with proteinase K resulted in the selective digestion of hyalin and was accompanied by release of the 45-kDa polypeptide from the layers. Washing intact layers in 20 mM Tris (pH 8.0) also resulted in the selective removal of hyalin and the 45-kDa polypeptide. The Ca2(+)-precipitable protein hyalin, alone among the hyaline layer polypeptides, bound the Ca2(+)-antagonist ruthenium red. These results suggest a structural organization within the hyaline layer that is both heterogenous and dynamic throughout embryonic development.