Sensory transduction in eukaryotes

Abstract

The organization of multicellular organisms depends on cell–cell communication. The signal molecules are often soluble components in the extracellular fluid, but also include odors and light. A large array of surface receptors is involved in the detection of these signals. Signals are then transduced across the plasma membrane so that enzymes at the inner face of the membrane are activated, producing second messengers, which by a complex network of interactions activate target proteins or genes [1]. Vertebrate cells have been used to study hormone and neurotransmitter action, vision, the regulation of cell growth and differentiation. Sensory transduction in lower eukaryotes is predominantly used for other functions, notably cell attraction for mating and food seeking. By comparing sensory transduction in lower and higher eukaryotes general principles may be recognized that are found in all organisms and deviations that are present in specialised systems. This may also help to understand the differences between cell types within one organism and the importance of a particular pathway that may or may not be general. In a practical sense, microorganisms have the advantage of their easy genetic manipulation, which is especially advantageous for the identification of the function of large families of signal transducing components.

Inducible expression of calmodulin antisense RNA in Dictyostelium cells inhibits the completion of cytokinesis.

“…Thus, the properties of Dictyostelium cells make them especially appropriate for examining the roles of calmodulin in motility. Furthermore, for many aspects of motility, biochemical data, ultrastructural information, and even mutants are already available (reviewed in Kessin, 1988;Egelhoff and Spudich, 1991;Jones et al, 1991;Van Haastert et al, 1991).…”

Selective induction of gene expression and second-messenger accumulation in Dictyostelium discoideum by the partial chemotactic antagonist 8-p-chlorophenylthioadenosine 3',5'-cyclic monophosphate.

“…This interaction results in activation of target enzymes, such as adenylate cyclase, guanylate cyclase, and phospholipase C (see ref. 9). Similar to the adrenergic receptor, for example, cAMP receptors are encoded by a family of different genes, of which three members have been cloned (10).…”

Control of 6-(d-threo-1′,2′-dihydroxypropyl) pterin (dictyopterin) synthesis during aggregation of Dictyostelium discoideum. Involvement of the G-protein-linked signalling pathway in the regulation of GTP cyclohydrolase I activity

“…In this model system the reaction mechanisms involved have to be identified further. Given the analogy between the Dictyostelium and mammalian G-protein signalling pathways [12,13] the results point to a possible similar role of G-proteins in the control of GTP cyclohydrolase I activity in mammalian cells. The present study shows that H % dictyopterin originates from GTP and our work focussed on the control of its biosynthesis by GTP cyclohydrolase I.…”

“…The aggregation process is coordinated by pulses of extracellular cyclic AMP (cAMP) which binds to cell-surface receptors and induces transient activation of several signal-transduction pathways. One of these causes the activation of adenylate cyclase (EC 4.6.1.1), inducing further synthesis and secretion of cAMP into the extracellular medium in the ' relay response ' (for review see [10][11][12][13]). This signalling pathway is linked to heterotrimeric G-proteins and involves the exchange of GTP for GDP on the For growth of D. discoideum amoebae, folate is an essential vitamin [14].…”