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Induction of ras gene expression by homologous aggregation factor in cells from the sponge Geodia cydonium.

1988; Elsevier BV; Volume: 263; Issue: 31 Linguagem: Inglês

10.1016/s0021-9258(18)37597-5

1083-351X

Heinz C. Schröder, Yoshiyuki Kuchino, Monika Gramzow, B. Kureleć, Ursula Friese, G. Uhlenbruck, Wernér E.G. Müller,

Calcium Carbonate Crystallization and Inhibition

Northern blot data as well as immunocytochemical and immunoblotting experiments indicate that the sponge Geodia cydonium contains the ras gene (or rasrelated gene).The ras gene transcript has a size of 1.5 kilobases and the ras gene product has an M, of 23,000-26,000.While dissociated G. cydonium cells lack ras gene product, ras gene expression can be induced by incubating the cells with the cell-binding fragment of the homologous aggregation factor.Maximal expression was observed 10-15 h after addition of the fragment.The sponge ras protein was partially purified by immunoprecipitation and bound GTP with a dissociation constant of 1.8 X lo-' M. It was found to be associated with the cell membrane.Autoradiographic studies revealed that the ras protein binds to the plasma membrane-associated anti-aggregation receptor and thereby mediates the mitogenic response, caused by the homologous lectin.It is hypothesized that sponges are provided in addition to the aggregation factor-caused and protein kinase C-mediated pathway with a second mechanism of transduction of mitotic signals, the lectin-caused and ras-mediated signaling.Since 1907 (Wilson, 1907) the sponge cell system has been widely used to study basic mechanisms of cell-cell interaction, also on the molecular level.During the last 15 years it became clear that only two species of molecules are required for the initial and species-specific contact of sponge cells: aggregation factor (AF)' and aggregation receptorfiaseplate (reviewed by Burger and Jumblatt, 1977;Muller, 1985).Two major cellmatrix interaction systems exist in sponges, which position the cells at their functional place; the molecules involved are the collagen-collagen assembly factor, and the lectin-antiaggregation factor (Muller et al., 1979b;Diehl-Seifert et al., 1985).Especially in the mesohyl compartment of the sponge organism, cell-matrix interactions predominate over cell-cell interactions (Garrone, 1978).Recently we described that the Geodia cydonium AF, after binding to the plasma membrane-bound aggregation receptor