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Nonmotile mutants of Myxococcus xanthus (Myxobacterales) failed to execute the morphogenetic movements required to shape a fruiting body. In addition, nonmotile mutants produced very few spores when plated for fruiting body development at cell densities appropriate for wild-type cells. At higher initial cell densities, the proportion of nonmotile cells that sporulate increased, indicating that one important function of motility in fruiting body development is to increase the local cell density. However, even at 10 times normal cell density, nonmotile cells sporulated at only 1% the wild-type level. This sporulation deficiency of nonmotile mutants accompanies an altered pattern of gene expression, monitored by using transcriptional fusions of lacZ to genes expressed at specific times during fruiting body development. Motility was not required for normal expression of five lac fusions that are expressed within the first 6 hr of fruiting-body development. However, the levels of expression from five lac fusions to later-expressed genes were reduced or abolished in nonmotile strains. beta-Galactosidase expression in these late Tn5 lac insertions was increased, and fruiting body development occurred in certain nonmotile strains that can be stimulated to move when mixed with a donor strain. This shows that motility itself is required because the stimulated cells are nonmotile genotypically. The nonmotile mutations had the same effect on developmental beta-galactosidase expression from these 10 lac fusions as an insertion mutation in the csg (formerly spoC) gene. csg mutants have a cell-cell interaction defect that blocks fruiting body development at approximately 6 hr. The similarity in the pattern of developmental expression of motility mutants and csg mutants suggests that motility is required for this csg-mediated cell-cell interaction.

Preparations of the catalytic subunit of cAMP-dependent protein kinase from rabbit skeletal muscle, which appear to be homogeneous by SDS-polyacrylamide gel electrophoresis, were often found to contain a hormone-like factor (HLF) which causes an immediate rise, then a decline of intracellular cAMP in a B-lymphoma cell line. Active HLF is released when the fractions that contain it in an inactive form are incubated with cAMP prior to chromatography, or passed through an immobilized cAMP column. HLF seems to be a peptide: it loses its cell-stimulating capability after proteolysis and has an apparent molecular mass of 2.2 – 2.5 kDa.

Spore formation in Bacillus subtilis relies on a regulated intramembrane proteolysis (RIP) pathway that synchronizes mother-cell and forespore development. To address the molecular basis of this SpoIV transmembrane signaling, we carried out a structure-function analysis of the activating protease CtpB. Crystal structures reflecting distinct functional states show that CtpB constitutes a ring-like protein scaffold penetrated by two narrow tunnels. Access to the proteolytic sites sequestered within these tunnels is controlled by PDZ domains that rearrange upon substrate binding. Accordingly, CtpB resembles a minimal version of a self-compartmentalizing protease regulated by a unique allosteric mechanism. Moreover, biochemical analysis of the PDZ-gated channel combined with sporulation assays reveal that activation of the SpoIV RIP pathway is induced by the concerted activity of CtpB and a second signaling protease, SpoIVB. This proteolytic mechanism is of broad relevance for cell-cell communication, illustrating how distinct signaling pathways can be integrated into a single RIP module.

Polybacterial diseases involve multiple organisms that act collectively to facilitate disease progression. Although this phenomenon was highlighted early in the 20th century, recent technological advances in diagnostics have led to the appreciation that many infections are far more complex than originally believed. Furthermore, it is apparent that although most treatments focus on the dominant bacterial species in an infection, other microbes, including commensals, can have a profound impact on both the response to therapy and virulence. Very little is known about the molecular mechanisms that underpin interactions between bacteria during such infections. Here, we discuss recent studies identifying and characterizing mechanisms of bacterial interaction and the biological processes they govern during certain diseases. We also highlight how possible strategies for targeting these interbacterial interactions may afford a route towards development of new therapies, with consequences for disease control.

Background Evolution has selected for organisms that benefit from genetically encoded cell-cell communication. Engineers have begun to repurpose elements of natural communication systems to realize programmed pattern formation and coordinate other population-level behaviors. However, existing engineered systems rely on system-specific small molecules to send molecular messages among cells. Thus, the information transmission capacity of current engineered biological communication systems is physically limited by specific biomolecules that are capable of sending only a single message, typically “regulate transcription.” Results We have engineered a cell-cell communication platform using bacteriophage M13 gene products to autonomously package and deliver heterologous DNA messages of varying lengths and encoded functions. We demonstrate the decoupling of messages from a common communication channel via the autonomous transmission of various arbitrary genetic messages. Further, we increase the range of engineered DNA messaging across semisolid media by linking message transmission or receipt to active cellular chemotaxis. Conclusions We demonstrate decoupling of a communication channel from message transmission within engineered biological systems via the autonomous targeted transduction of user-specified heterologous DNA messages. We also demonstrate that bacteriophage M13 particle production and message transduction occurs among chemotactic bacteria. We use chemotaxis to improve the range of DNA messaging, increasing both transmission distance and communication bit rates relative to existing small molecule-based communication systems. We postulate that integration of different engineered cell-cell communication platforms will allow for more complex spatial programming of dynamic cellular consortia.

Cardiovascular tissue engineering (CVTE) aims to create living tissues, with the ability to grow and remodel, as replacements for diseased blood vessels and heart valves. Despite promising results, the (long-term) functionality of these engineered tissues still needs improvement to reach broad clinical application. The functionality of native tissues is ensured by their specific mechanical properties directly arising from tissue organization. We therefore hypothesize that establishing a native-like tissue organization is vital to overcome the limitations of current CVTE approaches. To achieve this aim, a better understanding of the growth and remodeling (G&R) mechanisms of cardiovascular tissues is necessary. Cells are the main mediators of tissue G&R, and their behavior is strongly influenced by both mechanical stimuli and cell–cell signaling. An increasing number of signaling pathways has also been identified as mechanosensitive. As such, they may have a key underlying role in regulating the G&R of tissues in response to mechanical stimuli. A more detailed understanding of mechano-regulated cell–cell signaling may thus be crucial to advance CVTE, as it could inspire new methods to control tissue G&R and improve the organization and functionality of engineered tissues, thereby accelerating clinical translation. In this review, we discuss the organization and biomechanics of native cardiovascular tissues; recent CVTE studies emphasizing the obtained engineered tissue organization; and the interplay between mechanical stimuli, cell behavior, and cell–cell signaling. In addition, we review past contributions of computational models in understanding and predicting mechano-regulated tissue G&R and cell–cell signaling to highlight their potential role in future CVTE strategies.

Laminins are heterotrimeric (alpha/beta/gamma) glycoproteins that form a major polymer within basement membranes. Different alpha, beta and gamma subunits can assemble into various laminin isoforms that have different, but often overlapping, distributions and functions. In this study, we examine the contributions of the laminin alpha subunits to the development of C. elegans. There are two alpha, one beta and one gamma laminin subunit, suggesting two laminin isoforms that differ by their alpha subunit assemble in C. elegans. We find that near the end of gastrulation and before other basement membrane components are detected, the alpha subunits are secreted between primary tissue layers and become distributed in different patterns to the surfaces of cells. Mutations in either alpha subunit gene cause missing or disrupted extracellular matrix where the protein normally localizes. Cell-cell adhesions are abnormal: in some cases essential cell-cell adhesions are lacking, while in other cases, cells inappropriately adhere to and invade neighboring tissues. Using electron microscopy, we observe adhesion complexes at improper cell surfaces and disoriented cytoskeletal filaments. Cells throughout the animal show defective differentiation, proliferation or migration, suggesting a general disruption of cell-cell signaling. The results suggest a receptor-mediated process localizes each secreted laminin to exposed cell surfaces and that laminin is crucial for organizing extracellular matrix, receptor and intracellular proteins at those surfaces. We propose this supramolecular architecture regulates adhesions and signaling between adjacent tissues.

In response to starvation, Myxococcus xanthus initiates a developmental program that results in the formation of spore-filled, multicellular fruiting bodies. Many developmentally regulated genes in M. xanthus are transcribed from σ 54 promoters, and these genes require enhancer-binding proteins. Here we report the finding of an unusual group of 12 genes encoding σ 54 -dependent enhancer-binding proteins containing a forkhead-associated (FHA) domain as their N-terminal sensory domain. FHA domains in other proteins recognize phosphothreonine residues. An insertion mutation in one of these genes, Mx4885 , caused a cell autonomous aggregation and sporulation defect. In-frame deletion mutants showed that the FHA domain is necessary for proper Mx4885 function. The altered pattern of developmental gene expression in the mutant implied that Mx4885 is on the pathway of response to the morphogenetic C-signal. Immunoblots specific for C-signal and FruA imply that the site of Mx4885 action is downstream of FruA synthesis on the C-signal transduction pathway. Mx4885 may help to coordinate the level of intracellular phosphorylated FruA (FruA-P) with the level of C-signal displayed on the signal donor cell. Because FHA domains respond to phosphothreonine-containing proteins, these results suggest a regulatory link to the abundant Ser/Thr protein kinases in M. xanthus .