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The role of two extracellular matrix glycoproteins in the development of the starfish Pisaster ochraceus Maghsoodi, Bita

Abstract

Cell-extracellular matrix (ECM) interactions are crucial for the development of the embryos. ECM provides an environment through which cells can migrate, and a substratum for their adhesion and guidance. In this study, cell-ECM interactions were investigated in early morphogenesis of the starfish Pisaster ochraceus. Two monoclonal antibodies (HL-1 and PM-2) generated against ECM components of the hyaline layer and the blastocoel, respectively, were used to identify, localize and characterize these components. Immunocytochemical studies using HL-1 antibody shows that HL-1 epitope is synthesized by the ectodermal cells from the early blastula stage to the bipinnaria stage, and is secreted into the hyaline layer. The epitope was first observed around the Golgi apparatus and deglycosylation of the epitope resulted in the loss of its antigenicity, implicating HL-1 as a glycoprotein. When embryos were incubated in seawater containing an antibody to block the function of the HL-1 antigen, show that the hyaline layer was exfoliated. The results indicated that this E CM component may play a role in development and maintenance of the structural integrity of the hyaline layer. Furthermore, embryos exposed to seawater containing the HL-1 antibody were unable to swim and failed to develop a proper GI tract. This indicated that the HL-1 epitope is necessary for ciliary activity and GI tract development. PM-2 epitope also showed the characteristics of a glycoprotein and it too appeared to be important in the development of starfish embryos. Immunofluorescence and immunogold studies showed that the PM-2 epitope was present in the cortical granules and it was synthesized by the early blastomeres through to the bipinnaria stage. These studies also showed that the PM-2 epitope was concentrated in the blastocoel, in the hyaline layer and in the lumen of the Gl tract. Functional blocking experiments using anti-PM-2 antibody revealed that the PM-2-perturbed embryos contained very few migratory mesenchyme cells and failed to develop a proper Gl tract. This indicated that the PM-2 epitope may play a role in mesenchyme cell migration, development of the Gl tract and overall growth ofthe embryo.

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