Thesis

Cell surface changes found in developing sea urchin embryos

Cell surface properties play an important role in embryonic morphogenesis and in malignant invasion. Cell surface sugar chains extend away from the cell membrane and are believed to be involved in cellular migration and adhesiveness. Some of these sugar complexes also act as receptor sites for lectins. Plant lectins are often used to detect these receptor sites on embryonic cells. At the 16 cell stage, sea urchin (Strongylocentrotus purpuratus) embryos exhibit cell size differentiation into larger cells (macromeres), medium sized cells (mesomeres) and smaller cells (micromeres). A difficulty in separating these embryos into single cells is the presence of a fertilization membrane. In this study, prior to fertilization the eggs were treated to prevent fertilization membrane formation. Following fertilization and development to the 16 cell stage, the embryos were disaggregated and the cell surface properties of the individual cells (macromeres, mesomeres and micromeres) were analyzed by their differential adhesiveness to agarose beads coated with various lectins. The results show that each of the three cell types of the 16 cell stage embryo have specific surface properties as indicated by their differential ability to bind to specific lectin beads. Moreover, the adhesive specificities demonstrated in this study for the 16 cell stage embryo differ somewhat from those of blastula stage embryos as reported in an earlier study from this laboratory. The results indicate that there is both a stage-specific and cell type-specific differentiation of cell surface sugar containing receptors that may be important in controlling morphogenetic events.

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