Mhp493 (P216) is a proteolytically processed, cilium and heparin binding protein of Mycoplasma hyopneumoniae

Mycoplasma hyopneumoniae induces respiratory disease in swine by colonizing cilia causing ciliostasis, cilial loss and epithelial cell death. Heparin binds to M. hyopneumoniae cells in a dose-dependent manner and blocks its ability to adhere to porcine cilia. We show here that Mhp493 (P216), a paralogue of the cilium adhesin P97 (Mhp183), is cleaved between amino acids 1040 and 1089 generating surface-accessible, heparin-binding proteins P120 and P85. Antiphosphoserine antibodies recognized P85 in 2-D immunoblotting studies and TiO₂ chromatography of trypsin digests of P85 isolated a single peptide with an m/z of 917.3. A phosphoserine residue in the tryptic peptide ⁹⁰VSELpSFR⁹⁶ (position 94 in P85) was identified by MALDI-MS/MS. Polyhistidine fusion proteins (F1_P216, F2_P216, F3_P216) spanning Mhp493 bound heparin with biologically significant Kd values, and heparin, fucoidan and mucin inhibited this interaction. Latex beads coated with F1_P216, F2_P216 and F3_P216 adhered to and entered porcine kidney epithelial-like (PK15) cell monolayers. Microtitre plate-based assays showed that sequences within P120 and P85 bind to porcine cilia and are recognized by serum antibodies elicited during infection by M. hyopneumoniae . Mhp493 contributes significantly to the surface architecture of M. hyopneumoniae and is the first cilium adhesin to be described that lacks an R1 cilium-binding domain.     

Synchronization properties of networks of electrically coupled neurons in the presence of noise and heterogeneities

We investigate how synchrony can be generated or induced in networks of electrically coupled integrate-and-fire neurons subject to noisy and heterogeneous inputs. Using analytical tools, we find that in a network under constant external inputs, synchrony can appear via a Hopf bifurcation from the asynchronous state to an oscillatory state. In a homogeneous net work, in the oscillatory state all neurons fire in synchrony, while in a heterogeneous network synchrony is looser, many neurons skipping cycles of the oscillation. If the transmission of action potentials via the electrical synapses is effectively excitatory, the Hopf bifurcation is supercritical, while effectively inhibitory transmission due to pronounced hyperpolarization leads to a subcritical bifurcation. In the latter case, the network exhibits bistability between an asynchronous state and an oscillatory state where all the neurons fire in synchrony. Finally we show that for time-varying external inputs, electrical coupling enhances the synchronization in an asynchronous network via a resonance at the firing-rate frequency.

Synthesis, antifungal, haemolytic and cytotoxic activities of a series of bis(alkylpyridinium)alkanes

A series of bis(alkylpyridinium)alkanes with a twelve carbon spacer between the positive charges was synthesised and their antifungal activity has been investigated. Compounds with 2-pentyl, 4-pentyl, 4-hexyl, 4-octyl, 4-propylbenzene, 3,4-dipentyl, 4-(5′-nonyl) and 3-methyl,4-pentyl head groups were the most potent antifungal agents with MICs in the range of 1.4–2.7 μM against reference strains of both Cryptococcus neoformans and Candida albicans.     

Leaf n‐Alkanes as Characters Differentiating Coastal and Continental Juniperus deltoides Populations from the Balkan Peninsula

The composition of the cuticular n‐alkanes isolated from the leaves of nine populations of Juniperus deltoides R.P.Adams from continental and coastal areas of the Balkan Peninsula was characterized by GC‐FID and GC/MS analyses. In the leaf waxes, 14 n‐alkane homologues with chain‐lengths ranging from C₂₂ to C₃₅ were identified. n‐Tritriacontane (C₃₃) was dominant in the waxes of all populations, but variations between the populations in the contents of all n‐alkanes were observed. Several statistical methods (ANOVA, principal component, discriminant, and cluster analyses) were used to investigate the diversity and variability of the cuticular‐leaf‐n‐alkane patterns of the nine J. deltoides populations. This is the first report on the n‐alkane composition for this species. The multivariate statistical analyses evidenced a high correlation of the leaf‐n‐alkane pattern with the geographical distribution of the investigated samples, differentiating the coastal from the continental populations of this taxon.     

How Difficult Is Inference of Mammalian Causal Gene Regulatory Networks?

Gene regulatory networks (GRNs) play a central role in systems biology, especially in the study of mammalian organ development. One key question remains largely unanswered: Is it possible to infer mammalian causal GRNs using observable gene co-expression patterns alone? We assembled two mouse GRN datasets (embryonic tooth and heart) and matching microarray gene expression profiles to systematically investigate the difficulties of mammalian causal GRN inference. The GRNs were assembled based on pieces of experimental genetic perturbation evidence from manually reading primary research articles. Each piece of perturbation evidence records the qualitative change of the expression of one gene following knock-down or over-expression of another gene. Our data have thorough annotation of tissue types and embryonic stages, as well as the type of regulation (activation, inhibition and no effect), which uniquely allows us to estimate both sensitivity and specificity of the inference of tissue specific causal GRN edges. Using these unprecedented datasets, we found that gene co-expression does not reliably distinguish true positive from false positive interactions, making inference of GRN in mammalian development very difficult. Nonetheless, if we have expression profiling data from genetic or molecular perturbation experiments, such as gene knock-out or signalling stimulation, it is possible to use the set of differentially expressed genes to recover causal regulatory relationships with good sensitivity and specificity. Our result supports the importance of using perturbation experimental data in causal network reconstruction. Furthermore, we showed that causal gene regulatory relationship can be highly cell type or developmental stage specific, suggesting the importance of employing expression profiles from homogeneous cell populations. This study provides essential datasets and empirical evidence to guide the development of new GRN inference methods for mammalian organ development.     

Two genes that regulate exopolysaccharide production in Rhizobium sp. strain NGR234: DNA sequences and resultant phenotypes.

Two closely linked genes involved in the regulation of exopolysaccharide (EPS) production in Rhizobium sp. strain NGR234, exoX and exoY, were sequenced, and their corresponding phenotypes were investigated. Inhibition of EPS synthesis occurred in wild-type strains when extra copies of exoX were introduced, but only when exoY had been deleted or mutated or was present at a lower copy number. Normal EPS synthesis occurred in Rhizobium sp. when both exoX and exoY were introduced on the same replicon. Surprisingly, the presence of multiple copies of exoY in exoY:: Tn5 mutants of NGR234 adversely affected cellular growth. This was apparent when exoY was introduced into exoY mutants on IncP1 vectors, where the copy number was approximately 10, but was not apparent when present on much larger R-prime plasmids with lower copy numbers (approximately 3 per cell). Multiple copies of exoX did not adversely affect cellular growth of any strain. The exoX gene appeared analogous, in size and phenotype, to a previously described Rhizobium leguminosarum biovar phaseoli EPS gene, psi (D. Borthakur and A.W.B. Johnston, Mol. Gen. Genet. 207:149-154, 1987), and the deduced ExoX and Psi shared strikingly similar secondary structures. Despite this, ExoX and Psi showed little homology at the primary amino acid level, except for a central region of 18 amino acids. The interaction of ExoX and ExoY could form the basis of a sensitive regulatory system for EPS acids. The interaction of ExoX and ExoY could form the basis of a sensitive regulatory system for EPS biosynthesis. The presence of a multicopy exoX in Rhizobium meliloti and R. fredii similarly abolished EPS biosynthesis in these species.