Ectoderm Cell–ECM Interaction Is Essential for Sea Urchin Embryo Skeletogenesis

Abstract

Paracentrotus lividus sea urchin nectin (Pl-nectin) is an extracellular matrix (ECM) protein of the sea urchin embryo on the apical surface of the ectoderm and has been shown to be an adhesive substrate for embryonic cells. A monoclonal antibody (McAb) to Pl-nectin was generated that inhibits the adhesion of blastula cells to Pl-nectin-coated substrates in an in vitro functional assay. To examine for possible in vivo functions of Pl-nectin, Fab fragments (Fabs) of Pl-nectin McAb were added to early blastulae. Ingression of primary mesenchyme cells was not affected by Fabs. As control embryos reached the pluteus stage, treated embryos showed a severe inhibition of skeletal elongation and patterning. When the Fabs were injected directly into the blastocoel, even at higher concentration than was applied externally, skeletogenesis was normal. Therefore, the effect of the antibody on spiculogenesis was indirect. The treatment was partially reversible as embryos eventually seemed to recover and elongate spicules, although with an incorrect patterning. Migration of pigment cells was also affected by the Fabs, since they did not disperse throughout the ectoderm but remained clustered in ectopic areas. In contrast, the development of endoderm structures was not affected. Our results indicate that in the sea urchin embryo the appropriate contact of ectodermal cells with outer ECM components is essential for the correct morphogenesis of inner mesodermal structures.

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“…Cell fates are fully specified by the blastula-early gastrula stage of development, when cells have begun to express particular sets of territory-specific genes (Davidson et al, 1998). Although maternal determinants are required for founder cell specification during development, interactions between the PMCs and external cues derived from the ectoderm specify many phases of the skeleton formation (Armstrong et al, 1993;Ettensohn & Malinda, 1993;Guss & Ettensohn, 1997;Zito et al, 1998). The blastula stage is characterized by the presence of a large fluid-filled blastocoels, surrounded by a single layer of cells.…”

Hierarchically Nanostructured Biological Materials

“…Without such a load-transfer mechanism, the individual platelets of the minerals would be exposed to extremely large mechanical loads and become more susceptible to mechanical failure [40,[55][56][57]. And the interactions between collagen bundles and fibrils, which are organic-organic interactions, are also important because [58], (c) Ji and Gao [66], (d) Sun and Bhusan [67], (e) Wilt [68], and (f) Zito et al [69].) the fiber bundles themselves are decorated by molecules that are electrostatically interacting, the so-called sacrificial bonds between bundles, and allows the bundles to shear between other bundles [58][59][60][61].…”

Pl-nectin, a discoidin family member, is a ligand for βC integrins in the sea urchin embryo

“…Embryos were cell surface biotinylated as described by Zito et al (1998). Briefly, embryos were washed twice in ice-cold MFSW and then incubated in a biotinylation reagent (ECL Protein Biotinylation Kit, Amersham) at 4°C for 30 min, according to manufacturer's instructions.…”

“…A number of ECM proteins have been identified in the hyaline layer, including Pl-nectin, which was originally purified from Paracentrotus lividus eggs and shown to be localized to the apical surface of cells of the ectoderm and endoderm germ layers (Alliegro et al, 1988;Matranga et al, 1992). This ECM protein is also involved in indirect signaling between ectoderm and mesoderm germ layers (Zito et al, 1998). Indeed, we have shown that ectoderm cells must interact with Pl-nectin in the hyaline layer to enable permissive signals that are necessary for skeletogenic mesenchyme in the blastocoel to correctly grow and pattern the skeleton (Kiyomoto et al, 2004;Zito et al, 1998Zito et al, , 2000Zito et al, , 2003.…”

“…This ECM protein is also involved in indirect signaling between ectoderm and mesoderm germ layers (Zito et al, 1998). Indeed, we have shown that ectoderm cells must interact with Pl-nectin in the hyaline layer to enable permissive signals that are necessary for skeletogenic mesenchyme in the blastocoel to correctly grow and pattern the skeleton (Kiyomoto et al, 2004;Zito et al, 1998Zito et al, , 2000Zito et al, , 2003. However, to date the molecular basis of the interaction between Pl-nectin and ectodermic cells remains unknown.…”