A Maltose-binding-protein-like Peptide Accumulates after Mixing Two Types of Sexually Competent Cells of a Cellular Slime Mold, Dictyostelium discoideum.

Abstract

A cellular slime mold, Dictyostelium discoideum is an ideal model organism for examining sexual differentiation and mating. Cells on agar plates can obtain sexual competence syn chronously by culturing in liquid medium including food bacteria with shaking. After removing the bacteria, mixing opposite mating type cells of D. discoideum results in beginning of mating. They fuse with each other, forming multinucleate cells. After giant cells are formed, they attract and engulf smaller cells. Giant cells develop into macrocysts. Macrocysts undergo meiosis and at the end of dormancy, their progeny amoebae are released. Though formation of multinuclear cells is unique, serial sexual events such as plasmogany, karyogamy, formation of thick wall, and meiosis are universal in the mating of isogamous organisms. Involvement of Ca2+, cAMP with mating is also the case in fertilizing green algae (Goodenough and Thoner 1983). Analysis of mating mechanism using Dictyostelium cell will reveal common mechanism among various organisms.Dictyostelium discoideum is one of the organisms that glycoproteins at mating are precisely studied as well as sea urchin (Gilbert 1988) 1987 , Ishikawa et al. 1991. These results suggest that sugars play important roles in the gamete differentiation and fusion of mating cells. But there have been a few immunological researches on sugar binding proteins of D. dis coideum, while many papers reported precisely roles of carbohydrates on cell membrane. In bacteria, maltose translocator upon cell membrane is a recognition target for infecting phage lambda (Randall-Hazelbauer and Schwartz 1973), and in human macrophages, mannose receptor mediates phagocytosis of saccharide-coated particles (Warr 1980).We have tried to detect maltose-binding protein in the cell of D. discoideum after beginning of mating using antibody to bacterial maltose-binding protein (MBP).This paper reports accumulation of two MBP-like peptides 24hr after mixing two types of sexually competent cells for the first time. We show morphology of mating cells in DAPI-fluorescence microscopy. We discuss about the nature of isoforms of MBP-like protein, and speculate their potential roles in