In the social amoebae Dictyostelium discoideum, periodic synthesis and release of extracellular cyclic AMP (cAMP) guides cell aggregation and commitment to form fruiting bodies. It is unclear whether these oscillations represent an intrinsic property of individual cells or if they only exist as a population-level phenomenon. Here we show by live-cell imaging of intact cell populations that pulses originate from a discrete location despite constant exchange of cells to and from the region. In a perfusion chamber, both isolated single cells and cell populations switch from quiescence to rhythmic activity depending on the level of extracellular cAMP. A quantitative analysis shows that stochastic pulsing of individual cells below the threshold concentration of extracellular cAMP plays a critical role in the onset of collective behavior.

Because intracellular processes are inherently noisy, stochastic reactions process noisy signals in cellular signal transduction. One essential feature of biological signal transduction systems is the amplification of small changes in input signals. However, small random changes in the input signals could also be amplified, and the transduction reaction can also generate noise. Here, we show theoretically how the abrupt response of ultrasensitive signal-transduction reactions results in the generation of large inherent noise and the high amplification of input noise. The inherently generated noise propagates with amplification through intracellular molecular network. We discuss how the contribution of such transmitted noise can be shown experimentally. Our results imply that the switch-like behavior of signal transduction could be limited by noise; however, high amplification reaction could be advantageous to generate large noise, which would be essential to maintain behavioral variability.

Highlights d Lateral root founder cells (LRFCs) express TOLS2 peptide, inhibiting nearby LRFCs d The receptor RLK7 and transcription factor PUCHI make up the TOLS2 signaling pathway d DR5, an LRFC marker, is occasionally activated in proximity to pre-existing LRFCs d TOLS2-RLK7-PUCHI inhibits LRFC identity in proximal cells, ensuring proper LR spacing SUMMARYIn plants, the position of lateral roots (LRs) depends on initiation sites induced by auxin. The domain of high auxin response responsible for LR initiation stretches over several cells, but only a pair of pericycle cells (LR founder cells) will develop into LRs.In this work, we identified a signaling cascade controlling LR formation through lateral inhibition. It comprises a peptide hormone TARGET OF LBD SIXTEEN 2 (TOLS2), its receptor RLK7, and a downstream transcription factor PUCHI. TOLS2 is expressed at the LR founder cells and inhibits LR initiation. Time-lapse imaging of auxin-responsive DR5:LUCIFERASE reporter expression revealed that occasionally two pairs of LR founder cells are specified in close proximity even in wild-type and that one of them exists only transiently and disappears in an RLK7-dependent manner. We propose that the selection of LR founder cells by the peptide hormone-receptor cascade ensures proper LR spacing.

A 4.2-kb DNA fragment conferring quinolone resistance was cloned from a quinolone-resistant clinical isolate of Staphylococcus aureus and was shown to possess a part of the grlB gene and a mutated grlA gene. S-80-->F and E-84-->K mutations in the grlA gene product were responsible for the quinolone resistance. The mutated grlA genes responsible for quinolone resistance were dominant over the wild-type allele, irrespective of gene dosage in a transformation experiment with the grlA gene alone. However, dominance by mutated grlA genes depended on gene dosage when bacteria were transformed with the grlA and grlB genes in combination. Quinolone-resistant gyrA mutants were easily isolated from a strain, S. aureus RN4220, carrying a plasmid with the mutated grlA gene, though this was not the case for other S. aureus strains lacking the plasmid. The elimination of this plasmid from such quinolone-resistant gyrA mutants resulted in marked increases in quinolone susceptibility. These results suggest that both DNA gyrase and DNA topoisomerase IV may be targets of quinolones and that the quinolone susceptibility of organisms may be determined by which of these enzymes is most quinolone sensitive.

Gene regulatory networks contain several substructures called network motifs, which frequently exist throughout the networks. One of such motifs found in Escherichia coli, Saccharomyces cerevisiae, and Drosophila melanogaster is the feed-forward loop, in which an effector regulates its target by a direct regulatory interaction and an indirect interaction mediated by another gene product. Here, we theoretically analyze the behavior of networks that contain feed-forward loops cross talking to each other. In response to levels of the effecter, such networks can generate multiple rise-and-fall temporal expression profiles and spatial stripes, which are typically observed in developmental processes. The mechanism to generate these responses reveals the way of inferring the regulatory pathways from experimental results. Our database study of gene regulatory networks indicates that most feed-forward loops actually cross talk. We discuss how the feed-forward loops and their cross talks can play important roles in morphogenesis.

Cancer stem cells (CSCs) drive tumor initiation and metastasis in several types of human cancer. However, the contribution of ovarian CSCs to peritoneal metastasis remains unresolved. The cell adhesion molecule CD44 has been identified as a major marker for CSCs in solid tumors, including epithelial ovarian cancer. CD44 exists as a standard form (CD44s) and also as numerous variant isoforms (CD44v) generated by alternative mRNA splicing. Here we show that disseminated ovarian tumors in the pelvic peritoneum contain highly enriched CD44v6-positive cancer cells, which drive tumor metastasis and are responsible for tumor resistance to chemotherapy. Clinically, an increased number of CD44v6-positive cancer cells in primary tumors was associated with a shortened overall survival in stage III–IV ovarian cancer patients. Furthermore, a subpopulation of CD44v6-positive cancer cells manifested the ability to initiate tumor metastasis in the pelvic peritoneum in an in vivo mouse model, suggesting that CD44v6-positive cells show the potential to serve as metastasis-initiating cells. Thus, the peritoneal disseminated metastasis of epithelial ovarian cancer is initiated by the CD44v6-positive subpopulation, and CD44v6 expression is a biomarker for the clinical outcome of advanced ovarian cancer patients. Given that a distinct subpopulation of CD44v6-positive cancer cells plays a critical role in peritoneal metastasis, definitive treatment should target this subpopulation of CD44v6-positive cells in epithelial ovarian cancer.

A series of imidazole-5-carboxylic acids bearing alkyl, alkenyl, and hydroxyalkyl substituents at the 4-position and their related compounds were prepared and evaluated for their antagonistic activities to the angiotensin II (AII) receptor. Among them, the 4-(1-hydroxyalkyl)-imidazole derivatives had strong binding affinity to the AII receptor and potently inhibited the AII-induced pressor response by intravenous administration. Various esters of these acids showed potent and long-lasting antagonistic activity by oral administration. The most promising compounds were (5-methyl-2-oxo-1,3-dioxol-4-yl)methyl (CS-866) and (pivaloyloxy)-methyl esters of 4-(1-hydroxy-1-methylethyl)-2-propyl-1-[(2'-1H-tetrazol-5- ylbiphenyl-4-yl)-methyl]imidazole-5-carboxylic acid (26c). A study involving stereochemical comparison of 26c with the acetylated C-terminal pentapeptide of AII was also undertaken.

During the initial stage of tumor progression, oncogenic cells spread despite spatial confinement imposed by surrounding normal tissue. This spread of oncogenic cells (winners) is thought to be governed by selective killing of surrounding normal cells (losers) through a phenomenon called "cell competition" (i.e., supercompetition). Although the mechanisms underlying loser elimination are increasingly apparent, it is not clear how winner cells selectively occupy the space made available following loser apoptosis. Here, we combined live imaging analyses of two different oncogenic clones (Yki/YAP activation and Ras activation) in the Drosophila epithelium with computer simulation of tissue mechanics to elucidate such a mechanism. Contrary to the previous expectation that cell volume loss after apoptosis of loser cells was simply compensated for by the faster proliferation of winner cells, we found that the lost volume was compensated for by rapid cell expansion of winners. Mechanistically, the rapid winner-dominated cell expansion was driven by apoptosis-induced epithelial junction remodeling, which causes re-connection of local cellular connectivity (cell topology) in a manner that selectively increases winner apical surface area. In silico experiments further confirmed that repetition of loser elimination accelerates tissue-scale winner expansion through topological changes over time. Our proposed mechanism for linking loser death and winner expansion provides a new perspective on how tissue homeostasis disruption can initiate from an oncogenic mutation.