Developmental Expression of Echinonectin, an Endogenous Lectin of the Sea Urchin Embryo

Abstract

Echinonectin (EN) is a galactose-binding lectin present in eggs and embryos of the sea urchin Lytechinus variegatus. Recent studies have suggested that EN is a hyaline layer protein that may function as a substrate adhesion molecule (SAM) during development. We have used monoclonal and affinitypurified polyclonal antibodies that specifically recognize this protein to determine its spatial and temporal expression during embryogenesis. EN is stored in granules or vesicles in the unfertilized egg. After fertilization, these granules are rapidly redistributed to the apical cytoplasm of the zygote. Our results show that at subsequent stages of development the lectin is expressed by cells of all three germ layers, including cells of the developing gut, coelomic pouches, and ectoderm, and by both primary and secondary rnesenchyme cells. In contrast to previous observations based solely upon light level immunofluorescent staining, immunoelectron microscopy demonstrates that EN is localized in intracellular, membrane-bounded vesicles. In epithelia1 cell types these vesicles have a highly polarized distribution and are found in the apical cortical cytoplasm. In rnesenchyrne cells the distribution of EN-containing vesicles is not obviously polarized. Steady-state levels of EN protein in the embryo remain almost constant from fertilization to the pluteus larva stage. Metabolic labeling studies show that synthesis of EN in L. variegatus begins immediately after fertilization and continues throughout embryogenesis. Monospecific antibodies raised against L. variegatus EN have also been used to determine whether this lectin is expressed in other echinoid species.

Calcium–protein interactions in the extracellular environment: Calcium binding, activation, and immunolocalization of a collagenase/gelatinase activity expressed in the sea urchin embryo

“…Gratwohl et al [1991] have demonstrated that toposome, a protein destined for export to the hyaline layer, is localized to both cortical and yolk granules in the unfertilized egg. Fuhrman et al [1992] have found that another hyaline layer protein, echinonectin, is localized to membrane-bound vesicles in the unfertilized egg. Similarly, in both Xenopus [Outenreath et al, 1988] and C. elegans [Creutz et al, 1996], exported proteins have been found in yolk granule-like structures in the unfertilized egg.…”

Mechanisms of the epithelial-to-mesenchymal transition in sea urchin embryos

“…8 An anti-Echinonectin mAb localizes the epitope on the basal side of hyalin and in the cytoplasmic, membrane-bound vesicles of all 3 blastomere descendants. 40 The protein structure contains a series of coagulation factor 5/8 repeats and discoidin-like lectin domains and bears similarity to the secreted proteins DEL-1 and lactadherin from angiogenic Figure 3. A Hyalin repeat (HYR) domain structure.…”

Purification and characterization of a T-antigen specific lectin from the coelomic fluid of a marine invertebrate, sea cucumber (Holothuria scabra)

“…However very few lectins are reported in echinoderms in comparison with those of other marine invertebrates. These include a few lectins from sea urchin, a sialic acid binding lectin belonging to the heat shock protein family [19], endogenous echinonectin from Lytechinus variegates [20], Lectin from Asterina pectinifera [21] and evidence for the involvement of lectin in the complement homologous immune system [4]. Sea cucumbers are echinoderms inhabitating relatively shallow coastal areas experiencing little or no currents.…”