Molecular Mechanisms of Adhesion in Dictyostelium

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Adhesion of cells within tissues is a basic cellular process that is common to all multicellular organisms. Dr. Loomis is focusing his attention on the mechanisms of cell-cell adhesion in Dictyostelium that function during aggregation and subsequent morphogenesis. He has shown that a surface glycoprotein, gp24, is synthesized during the first few hours of development. Antibodies specific to gp24 block adhesion during this period and this activity can be neutralized by highly purified gp24. A cloned protein of the gene coding for gp24 was ligated downstream to an actin promoter such that antisense RNA would be generated. Both synthesis of gp24 and the acquisition of cell-cell adhesion is delayed about four hours in cell transformed with this vector. Dr. Loomis proposes to delete the pair of genes coding for gp24 by gene replacement in both wild type strains and in strains specifically lacking the second adhesion mechanism (contact sites A). The consequences of a complete lack of gp24 throughout development will be fully determined with respect to morphogenesis and subsequent developmental gene expression. Following aggregation another adhesion mechanism appears in prespore cells that can be distinguished from the first two mechanisms by the adhesion blocking activity of specific antisera. Dr. Loomis proposes to fully characterize the essential component(s) of the third adhesion mechanism.