Extracellular matrix of sea urchin and other marine invertebrate embryos

Abstract

The extracellular matrix surrounding the sea urchin embryo (outer ECM) contains fibers and granules of various sizes which are organized in recognizable patterns as shown by ultrastructural studies, particularly stereoimaging techniques. The use of the ruthenium red method for retaining and staining the ECM, with modifications of the Luft (Anatomical Record 171:347-368, 1971) method for invertebrate embryos, allows for the clarification of certain structures, particularly fiber compaction in the interzonal region, and microvillus-associated bodies. The inner ECM in the sea urchin embryo includes the basal lamina and blastocoel matrix. Stereoimages show that the fibers which are loosely distributed in the blastocoel matrix become compacted around the periphery of the blastocoel to form the basal lamina. The ruthenium red method was also used on a number of marine invertebrate embryos and larvae, representing different phyla, to facilitate comparisons between their surface coats. The similarities observed in the specimens shown suggest that ECMs are widely found on marine invertebrate eggs, embryos, and larvae, and that they resemble vertebrate ECMs and may, therefore, have similar functions.

Ultrastructural study of the hyaline layer of the starfish embryo, Pisaster ochraceus

“…Specialized, dense caplike structures or microvillus associated bodies (MVAB's), similar to those previously described in the echinoid by Spiegel et al (1989), were at the level of the boundary sublayer in association with the tips of the cell surface microvilli. The MVAB of the asteroid, prepared by freeze substitution, consisted of two components-an electron-dense material lining the internal surface of the microvillus plasmalemma and an electron-dense ECM covering the external surface, the external cap (Fig.…”

“…Specialized ECM structures a t the tip of each microvillus resemble the microvillus associated bodies (MVAB's) described in other echinoderms (Spiegel et al, 1989) and the dense matrix a t the tips of the microvilli in the chicken intestinal mucosa (Mooseker and Tilney, 1975). Like the latter, filaments run the length of the asteroid microvilli and may terminate in the dense material inside the plasmalemma of each microvillus tip.…”

“…However, improved fixation techniques demonstrated a two-tiered structure (Wolpert and Mercer, 1963;Spiegel et al, 1989). Later work has shown that the HL consists of at least three to four sublayers (Lundgren, 1973;Morrill et al, 1987).…”

The microvilli and hyaline layer of embryonic asteroid epithelial collar cells: A sensory structure to determine the position of locomotory cilia?

“…Although these studies have demonstrated even greater detail in the HL than earlier studies which utilized conventional fixation or fixation with anionic dyes (Crawford and Abed, 1986;Spiegel et al, 1989), none of these studies have examined the relationship between the ECM of the hyaline layer and the microvilli in the collars and the cilia. The present paper involves SEM and TEM studies of conventionally fixed material and material preserved by freeze substitution in the presence of alcian blue, the results of which have been used to build a detailed picture of the structure and arrangement of the ECM of the collar and its association with the microvilli and the apical cellular surface.…”

Blastula wall invagination examined on the basis of shape behavior of vesicular objects with laminar envelopes

“…The blastula wall can be considered as a laminar structure because it involves not only a central layer constituted by the monocellular epithelial sheet but also a basolateral layer and several apical layers (Spiegel et al, 1989). Lane et al (1993), in their gel swelling mechanism of epithelial invagination, proposed the lateral swelling of the apical lamina, caused by the cell secretion of a hygroscopic substance, to be the reason for the bending of the epithelial sheet.…”