Pattern formation: fruiting body morphogenesis in Myxococcus xanthus

When Myxococcus xanthus cells are exposed to starvation, they respond with dramatic behavioral changes. The expansive swarming behavior stops and the cells begin to aggregate into multicellular fruiting bodies. The cell-surface-associated C-signal has been identified as the signal that induces aggregation. Recently, several of the components in the C-signal transduction pathway have been identified and behavioral analyses are beginning to reveal how the C-signal modulates cell behavior. Together, these findings provide a framework for understanding how a cell-surface-associated morphogen induces pattern formation.     

Cell behavior and cell-cell communication during fruiting body morphogenesis in Myxococcus xanthus

Formation of spatial patterns of cells from a mass of initially identical cells is a recurring theme in developmental biology. The dynamics that direct pattern formation in biological systems often involve morphogenetic cell movements. An example is fruiting body formation in the gliding bacterium Myxococcus xanthus in which an unstructured population of identical cells rearranges into an asymmetric, stable pattern of multicellular fruiting bodies in response to starvation. Fruiting body formation depends on changes in organized cell movements from swarming to aggregation. The aggregation process is induced and orchestrated by the cell-surface associated 17 kDa C-signal protein. C-signal transmission depends on direct contact between cells. Evidence suggests that C-signal transmission is geometrically constrained to cell ends and that productive C-signal transmission only occurs when cells engage in end-to-end contacts. Here, we review recent progress in the understanding of the pattern formation process that leads to fruiting body formation. Gliding motility in M. xanthus involves two polarly localized gliding machines, the S-machine depends on type IV pili and the A-machine seems to involve a slime extrusion mechanism. Using time-lapse video microscopy the gliding motility parameters controlled by the C-signal have been identified. The C-signal induces cells to move with increased gliding speeds, in longer gliding intervals and with decreased stop and reversal frequencies. The combined effect of the C-signal dependent changes in gliding motility behaviour is an increase in the net-distance travelled by a cell per minute. The identification of the motility parameters controlled by the C-signal in combination with the contact-dependent C-signal transmission mechanism have allowed the generation of a qualitative model for C-signal induced aggregation. In this model, the directive properties of the C-signal are a direct consequence of the contact-dependent signal-transmission mechanism, which is a local event involving direct contact between cells that results in a global organization of cells. This pattern formation process does not depend on a diffusible substance. Rather it depends on a cell-surface associated signal to direct the cells appropriately.     

C-factor: a cell-cell signaling protein required for fruiting body morphogenesis of M. xanthus

During fruiting body development, the product of the csgA gene is necessary for cellular aggregation, for spore differentiation, and for gene expression that is initiated after 6 hr of starvation. From nascent wild-type fruiting bodies we have purified a polypeptide of 17 kd called C-factor, which, at approximately 1 to 2 nM, restores normal development to csgA mutant cells. C-factor activity is not recovered from extracts of unstarved, growing cells or csgA mutant cells. The amino acid sequence from purified C-factor demonstrates that it is the product of the csgA gene. C-factor is active over a narrow range of concentration and has properties of a morphogenetic paracrine signal.     

Characterization of developmental autolysis in myxobacterial fruiting body morphogenesis with profiling of amino acids using capillary electrophoresis method

Summary. Capillary electrophoresis equipped with Laser-induced fluorescence (CE-LIF), combining with micro-culture technique was employed to determine extracellular amino acids in single myxobacterial fruiting body morphogenesis. The result showed that in the early aggregation stage, there was a remarkable increase of extracellular amino acids, which was produced by developmentally induced autolysis. The amino acids were then consumed by the vegetative cells in aggregation stage. In the following developmental events, the extracellular amino acids were kept at low level, which indicated that in the stages of fruiting body formation and myxospore development, there was no further cell autolysis. Using this novel method may provide detailed insight into the mechanisms of the developmental phenomena.     

Protein expression during Flammulina velutipes fruiting body formation

Formation of the Flammulina velutipes fruiting body can be induced by lowering the ambient temperature (first treatment) in complete darkness. Fruiting bodies formed under these conditions elongate without pileus formation (pinhead fruiting body), suggesting that they cannot mature in complete darkness. However, after light treatment of the pinhead fruiting body (second treatment), a pileus develops immediately, and the stipe also thickens and becomes increasingly pigmented. The apical region swells as a result of cell division starting 2 days after light treatment, the pileus–stipe junction fracture and hymenium primordia form on day 4, and gills appear at day 6. Pf1 and Pf3 are specifically expressed after exposure to low temperature without light. The cell wall-associated protein [pileus-specific hydrophobin-like protein (PSH)] is specifically induced in the pileus, but not in the stipe, following the second light treatment to the pinhead fruiting body. These results suggest that Pf1 and Pf3 would be involved in fruiting body induction and that PSH would be involved in pileus formation. These phenomena will aid further histological and molecular biological investigations into the mechanisms behind fruiting body development in F. velutipes.     

Spatial organization of Myxococcus xanthus during fruiting body formation

Microcinematography was used to examine fruiting body development of Myxococcus xanthus. Wild-type cells progress through three distinct phases: a quiescent phase with some motility but little aggregation (0 to 8 h), a period of vigorous motility leading to raised fruiting bodies (8 to 16 h), and a period of maturation during which sporulation is initiated (16 to 48 h). Fruiting bodies are extended vertically in a series of tiers, each involving the addition of a cell monolayer on top of the uppermost layer. A pilA (MXAN_5783) mutant produced less extracellular matrix material and thus allowed closer examination of tiered aggregate formation. A csgA (MXAN_1294) mutant exhibited no quiescent phase, aberrant aggregation in phase 2, and disintegration of the fruiting bodies in the third phase.     

Dynamics of behaviour during neuronal morphogenesis in culture

We report a developmental sequence in the type and frequency of behaviours of neurons differentiating in vitro. We characterised these changes with extensive analysis of time-lapse sequences from both the continuing cell line pheochromocytoma PC12 and primary mixed cell culture of cat and mouse central nervous system. PC12 cells activated by nerve growth factor (NGF) differentiate in a uniform and synchronous manner. This allowed the first quantification of changes in different neuron behaviours during morphogenesis. Shortly after NGF activation, PC12 cells are highly labile in morphology and exhibit a large variety of morphological behaviours. During the first week of differentiation, the frequency of these behaviours declines, and gross morphology becomes more stable. The frequency of neurite initiation after 1 week in NGF is one-seventh what it was after 2 days in NGF. Over the same period, neurite retraction declines to one-third, and somal migration ceases altogether. Growth-cone activity does not decline during development. These behaviour changes correlate with published data on the differentiation of the neurite cytoskeleton. A qualitatively similar ontogeny was noted in the differentiation of CNS neurons in mixed cell culture. Major differences occur in the relative timing of changes in behaviours. Mature, stable morphology is not detected in these cultures until 7 weeks in vitro.     

Biologically active constituents from the fruiting body of Taiwanofungus camphoratus

Five new benzenoids, benzocamphorins A-E (1-5), and 10 recently isolated triterpenoids, camphoratins A-J (16-25), together with 23 known compounds including seven benzenoids (6-12), three lignans (13-15), and 13 triterpenoids (26-38) were isolated from the fruiting body of Taiwanofungus camphoratus. Their structures were established by spectroscopic analysis. Selected compounds were examined for cytotoxic and anti-inflammatory activities. Compounds 9 and 21 showed moderate cytotoxicity against MCF-7 and Hep2 cell lines with ED₅₀ values of 3.4 and 3.0 ??g/mL, respectively. Compounds 21, 25, 26, 29-31, 33, and 36 demonstrated potent anti-inflammatory activity by inhibiting lipopolysaccharide (LPS)-induced nitric oxide (NO) production with IC₅₀ values of 2.5, 1.6, 3.6, 0.6, 4.1, 4.2, 2.5, and 1.5 ??M, respectively, which were better than those of the nonspecific nitric oxide synthase (NOS) inhibitor N-nitro-l-arginine methyl ester (l-NAME) (IC₅₀: 25.8 ??M). These results may substantiate the use of T. camphoratus in traditional Chinese medicine (TCM) for the treatment of inflammation and cancer-related diseases. The newly discovered compounds deserve further development as anti-inflammatory candidates.     

Scanning electron microscopy of fruiting body formation by myxobacteria.

Scanning electron microscopy was used to follow fruiting body formation by pure cultures of Chondromyces crocatus M38 and Stigmatella aurantica. Vegetative cells were grown on SP agar and then transferred to Bonner salts agar for fructification. Fruiting in both species commences with the formation of aggregation centers which resemble a fried egg in appearance. In Chondromyces the elevated center or "yolk" region of the aggregation enlarges into a bulbous structure under which the stalk forms and lengthens. At maximum stalk height the bulb extends laterally as bud-like swellings appear. These are immature sporangia and are arranged in a distintive radial pattern around the top of the stalk. This symmetry is lost as more sporangia are formed. Stigmatella does not form a bulb; rather the yolk region of the aggregation center projects upward to form a column-like stalk which is nearly uniform in diameter throughout its length. At maximum stalk height, the terminus of the stalk develops an irregular pattern of bud-like swellings. These differentiate into sporangia. Stalks of 2-week-old mature fruiting bodies of both species appear to be cellular in composition. Stereomicrographs suggest orientation of these cells parallel to the long axis of the stalk. Stalks of 8-week-old fruiting bodies of Chondromyces were acellular and consisted of empty tubules, suggesting that the cells undergo degeneration with aging of the fruiting body.     

Fomitiporia ellipsoidea has the largest fruiting body among the fungi

A giant polypore, Fomitiporia ellipsoidea, was found in Hainan Island in southern China. It was 20 y old, and its estimated volume was 409?000-525?000cm(3) and weight was 400-500kg. This is the first report of the largest fungal fruiting body both in volume and weight.     

Beta-D-Allose inhibits fruiting body formation and sporulation in Myxococcus xanthus

Myxococcus xanthus, a gram-negative soil bacterium, responds to amino acid starvation by entering a process of multicellular development which culminates in the assembly of spore-filled fruiting bodies. Previous studies utilizing developmental inhibitors (such as methionine, lysine, or threonine) have revealed important clues about the mechanisms involved in fruiting body formation. We used Biolog phenotype microarrays to screen 384 chemicals for complete inhibition of fruiting body development in M. xanthus. Here, we report the identification of a novel inhibitor of fruiting body formation and sporulation, beta-d-allose. beta-d-Allose, a rare sugar, is a member of the aldohexose family and a C3 epimer of glucose. Our studies show that beta-d-allose does not affect cell growth, viability, agglutination, or motility. However, beta-galactosidase reporters demonstrate that genes activated between 4 and 14 h of development show significantly lower expression levels in the presence of beta-d-allose. Furthermore, inhibition of fruiting body formation occurs only when beta-d-allose is added to submerged cultures before 12 h of development. In competition studies, high concentrations of galactose and xylose antagonize the nonfruiting response to beta-d-allose, while glucose is capable of partial antagonism. Finally, a magellan-4 transposon mutagenesis screen identified glcK, a putative glucokinase gene, required for beta-d-allose-mediated inhibition of fruiting body formation. Subsequent glucokinase activity assays of the glcK mutant further supported the role of this protein in glucose phosphorylation.     

DIF-1 induces the basal disc of the Dictyostelium fruiting body

The polyketide DIF-1 induces Dictyostelium amoebae to form stalk cells in culture. To better define its role in normal development, we examined the phenotype of a mutant blocking the first step of DIF-1 synthesis, which lacks both DIF-1 and its biosynthetic intermediate, dM-DIF-1 (des-methyl-DIF-1). Slugs of this polyketide synthase mutant (stlB⁻) are long and thin and rapidly break up, leaving an immotile prespore mass. They have ∼ 30% fewer prestalk cells than their wild-type parent and lack a subset of anterior-like cells, which later form the outer basal disc. This structure is missing from the fruiting body, which perhaps in consequence initiates culmination along the substratum. The lower cup is rudimentary at best and the spore mass, lacking support, slips down the stalk. The dmtA⁻ methyltransferase mutant, blocked in the last step of DIF-1 synthesis, resembles the stlB⁻ mutant but has delayed tip formation and fewer prestalk-O cells. This difference may be due to accumulation of dM-DIF-1 in the dmtA⁻ mutant, since dM-DIF-1 inhibits prestalk-O differentiation. Thus, DIF-1 is required for slug migration and specifies the anterior-like cells forming the basal disc and much of the lower cup; significantly the DIF-1 biosynthetic pathway may supply a second signal - dM-DIF-1.