Spatial and temporal expression of a Polysphondylium spore-specific gene. (1/29)

In the cellular slime mold Polysphondylium spherical masses of cells are periodically released from the base of the culminating sorogen. These whorls undergo a morphogenetic transformation from spherical to radial symmetry, marked by the early emergence of a radially symmetric prepattern on the whorl surface. In previous experiments, morphogenesis was followed by observing prestalk cell markers. Here we describe the isolation and characterization of a spore coat gene whose expression pattern is the negative image of the prestalk pattern. To study the molecular mechanism of sp-45 gene regulation, we have cloned and analyzed the sp-45 promoter. Deletion analysis localized a single positive regulatory element (PRE) to a 106-bp fragment between positions -246 and -352 of the upstream coding sequence. This fragment can be further divided into a promoter-proximal and promoter-distal PRE and a 29-bp sequence between them. The distal PRE can regulate prespore expression when fused to a nonfunctioning basal promoter. The distal PRE contains two adjacent essential elements, a Gr box (GTGATATAGTGG) and a TA box (TAATATATT). Each element can drive prespore cell-specific reporter gene expression independently when incorporated into a nonfunctional promoter. Our results also show that prespore cell-specific gene expression is solely under positive regulation, with no evidence for spore-specific enhancers or cis-acting negative regulatory elements. By fusing GFP to the C-terminus of sp-45, we have demonstrated that the graded gene expression of SP45 in the sorogen is regulated by a sequence lying within the sp-45 coding sequence. The temporal and spatial expression pattern of this protein, taken together with the prestalk expression pattern, demonstrates unambiguously that the radial symmetries that emerge in the whorl are established by a system of positional coordinates and that cell sorting plays little if any role in this process.  (+info)

Structure determination and total synthesis of a novel antibacterial substance, AB0022A, produced by a cellular slime mold. (2/29)

A novel antibacterial substance, AB0022A, was isolated from the cellular slime mold Dictyostelium purpureum K1001. It inhibited the growth of Gram-positive bacteria, and its MICs ranged from 0.39 to 50 microg/ml. Because AB0022A was a highly substituted aromatic compound, we could not determine its structure based on only its physico-chemical and spectral data. We therefore used a dehalogenated derivative from AB0022A and deduced that its structure was 1,9-dihydroxy-3,7-dimethoxy-2-hexanoyl-4,6,8-trichlorodibenzofuran . To confirm this structure, we synthesized the compound having the deduced structure. The synthetic compound was identical to naturally occurring AB0022A.  (+info)

Characterization of two unusual guanylyl cyclases from dictyostelium. (3/29)

Guanylyl cyclase A (GCA) and soluble guanylyl cyclase (sGC) encode GCs in Dictyostelium and have a topology similar to 12-transmembrane and soluble adenylyl cyclase, respectively. We demonstrate that all detectable GC activity is lost in a cell line in which both genes have been inactivated. Cell lines with one gene inactivated were used to characterize the other guanylyl cyclase (i.e. GCA in sgc(minus sign) null cells and sGC in gca(minus sign) null cells). Despite the different topologies, the enzymes have many properties in common. In vivo, extracellular cAMP activates both enzymes via a G-protein-coupled receptor. In vitro, both enzymes are activated by GTPgammaS (K(a) = 11 and 8 microm for GCA and sGC, respectively). The addition of GTPgammaS leads to a 1.5-fold increase of V(max) and a 3.5-fold increase of the affinity for GTP. Ca(2+) inhibits both GCA and sGC with K(i) of about 50 and 200 nm, respectively. Other biochemical properties are very different; GCA is expressed mainly during growth and multicellular development, whereas sGC is expressed mainly during cell aggregation. Folic acid and cAMP activate GCA maximally about 2.5-fold, whereas sGC is activated about 8-fold. Osmotic stress strongly stimulates sGC but has no effect on GCA activity. Finally, GCA is exclusively membrane-bound and is active mainly with Mg(2+), whereas sGC is predominantly soluble and more active with Mn(2+).  (+info)

Element analysis of the Polysphondylium pallidum gp64 promoter. (4/29)

gp64 mRNA in Polysphondylium pallidum is expressed extensively during vegetative growth, and begins to rapidly decrease at the onset of development. To examine this unique regulation, 5' deletion analysis of the gp64 promoter was undertaken, and two growth-phase activated elements have been found: a food-dependent, upstream regulatory region (FUR, -222 to -170) and a vegetatively activated, downstream region (VAD, -110 to -63). Here we concentrate our analysis on an A1 and A2 sequences in the FUR region: A1 consists of a GATTTTTTTA sequence called a corresponding sequence and A2 consists of the direct repeat TTTGTTGTG. The cells carrying a combined construct of A1 and A2 acted synergistically in a reporter activity. A point mutation analysis in A1 indicates that a G residue is required for the activation of A1. From analyses of promoter regulation in a liquid or a solid medium, the promoter activity of the cells fed on bacteria in A-medium (axenic medium for Polysphondylium) or grown in A-medium alone was only one fourth of that of the cells fed on bacteria. By the gel retardation, we detected a protein bound to the A1 sequence.  (+info)

On the origin of differentiation. (5/29)

Following the origin of multicellularity in many groups of primitive organisms there evolved more than one cell type. It has been assumed that this early differentiation is related to size the larger the organism the more cell types. Here two very different kinds of organisms are considered: the volvocine algae that become multicellular by growth, and the cellular slime moulds that become multicellular by aggregation. In both cases there are species that have only one cell type and others that have two. It has been possible to show that there is a perfect correlation with size: the forms with two cell types are significantly larger than those with one. Also in both groups there are forms of intermediate size that will vary from one to two cell types depending on the size of the individuals, suggesting a form of quorum sensing. These observations reinforce the view that size plays a critical role in influencing the degree of differentiation.  (+info)

Identification of a penicillin-sensitive carboxypeptidase in the cellular slime mold Dictyostelium discoideum. (6/29)

Penicillin binding proteins (PBPs) are penicillin-sensitive DD-peptidases catalyzing the terminal stages of bacterial cell wall assembly. We identified a Dictyostelium discoideum gene that encodes a protein of 522 amino acids showing similarity to Escherichia coli PBP4. The D. discoideum protein conserves three consensus sequences (SXXK, SXN and KTG) that are responsible for the catalytic activities of PBPs. The gene product prepared in the cell-free translation system showed carboxypeptidase activity but the activity was not detected in the presence of penicillin G. These results demonstrate that the D. discoideum gene encodes a eukaryotic form of penicillin-sensitive carboxypeptidase.  (+info)

Evolution of cooperation: two for one? (7/29)

How can cooperation thrive in a selfish world? Recent evolution experiments show how bacteria themselves can generate conditions that make cooperation a winning strategy. At least in the short term.  (+info)

New bisindole alkaloids isolated from Myxomycetes Arcyria cinerea and Lycogala epidendrum. (8/29)

Two new bisindole alkaloids, named cinereapyrrole A (1) and B (2), were isolated from wild fruit bodies of Arcyria cinerea and three new bisindole alkaloids (3-5) were isolated from wild fruit bodies of Lycogala epidendrum. Seven known bisindoles (6-12) were concomitantly obtained from them. The structures of the new compounds were elucidated by spectral data. Among these bisindole alkaloids, compound 12 showed cytotoxicity against cultured tumor cell lines.  (+info)