A Chemoattractant Receptor Controls Development in Dictyostelium discoideum

Abstract

During the early stages of its developmental program, Dictyostelium discoideum expresses cell surface cyclic adenosine monophosphate (cyclic AMP) receptors. It has been suggested that these receptors coordinate the aggregation of individual cells into a multicellular organism and regulate the expression of a large number of developmentally regulated genes. The complementary DNA (cDNA) for the cyclic AMP receptor has now been cloned from lambda gt-11 libraries by screening with specific antiserum. The 2-kilobase messenger RNA (mRNA) that encodes the receptor is undetectable in growing cells, rises to a maximum at 3 to 4 hours of development, and then declines. In vitro transcribed complementary RNA, when hybridized to cellular mRNA, specifically arrests in vitro translation of the receptor polypeptide. When the cDNA is expressed in Dictyostelium cells, the undifferentiated cells specifically bind cyclic AMP. Cell lines transformed with a vector that expresses complementary mRNA (antisense) do not express the cyclic AMP receptor protein. These cells fail to enter the aggregation stage of development during starvation, whereas control and wild-type cells aggregate and complete the developmental program within 24 hours. The phenotype of the antisense transformants suggests that the cyclic AMP receptor is essential for development. The deduced amino acid sequence of the receptor reveals a high percentage of hydrophobic residues grouped in seven domains, similar to the rhodopsins and other receptors believed to interact with G proteins. It shares amino acid sequence identity and is immunologically cross-reactive with bovine rhodopsin. A model is proposed in which the cyclic AMP receptor crosses the bilayer seven times with a serine-rich cytoplasmic carboxyl terminus, the proposed site of ligand-induced receptor phosphorylation.

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

“…Reduction of mRNA levels by the introduction of vectors producing antisense RNA also has proved effective. The Dictyostelium genes whose expression has been blocked by antisense RNA include discoidin I (Crowley et al, 1985), myosin II heavy chain (Knecht and Loomis, 1987) and essential light chain (Pollenz et al, 1992), cAMP receptor (Klein et al, 1988;Sun et al, 1990), D2 esterase (Rubino et al, 1989), gp24 (Loomis and Fuller, 1991), V4 (McPherson and Singleton, 1992), and conditioned medium factor (CMF) (Jain et al, 1992).…”

amiB, a novel gene required for the growth/differentiation transition in Dictyostelium

“…The expression levels of CprD decrease immediately after the onset of differentiation in wild-type cells . The acaA and carA gene encodes ACA and cAR1, respectively (Klein et al 1988;Pitt et al 1992); both of these gene products are components of the cAMP-signalling ; amiB À /acaA (closed circles); amiB À /Ddmyb2 (closed squares). Cells were starved in suspension and pulsed with 30-nM cAMP added every 6 min for 5±6 h and assayed for (A) cAMP-mediated cGMP response and (B) cAMP-relay response.…”

“…Nutrient depletion triggers the differentiation of Dictyostelium cells through the transcriptional inactivation of some growth-phase genes, as well as through the transcriptional activation of essential genes required for the aggregation of the cells. The expression of some of the components constituting the cAMP-signalling system, such as cAR1 and ACA, is induced at the growth/differentiation transition stage (Klein et al 1988;Pitt et al 1992). These aggregative genes are initially expressed at low levels in response to starvation or to cell density-sensing agents such as the prestarvation factor (PSF) and the conditioned medium factor (CMF) (Mann & Firtel 1989;Gomer et al 1991;Rathi & Clarke 1992).…”

A developmentally regulated gene product from Dictyostelium discoideum shows high homology to human α‐L‐fucosidase

“…The D. discoideum A11H2 sequence may correspond to only one of the subunits of the human enzyme. The AllH2 protein seems to be controlled by the same cAMP-receptor mediated regulatory mechanisms as a number of other proteins that are maximally expressed in aggregating cells, for instance the contact site A cell adhesion protein [8,9] and cell-surface cAMP receptors [1,27]. Promoter elements responsible for the cAMP-dependent regulation of the A1 IH2 gene have been identified (May, T. et al, in preparation).…”