Polar invasion and translocation of Neisseria meningitidis and Streptococcus suis in a novel human model of the blood-cerebrospinal fluid barrier

Acute bacterial meningitis is a life-threatening disease in humans. Discussed as entry sites for pathogens into the brain are the blood-brain and the blood-cerebrospinal fluid barrier (BCSFB). Although human brain microvascular endothelial cells (HBMEC) constitute a well established human in vitro model for the blood-brain barrier, until now no reliable human system presenting the BCSFB has been developed. Here, we describe for the first time a functional human BCSFB model based on human choroid plexus papilloma cells (HIBCPP), which display typical hallmarks of a BCSFB as the expression of junctional proteins and formation of tight junctions, a high electrical resistance and minimal levels of macromolecular flux when grown on transwell filters. Importantly, when challenged with the zoonotic pathogen Streptococcus suis or the human pathogenic bacterium Neisseria meningitidis the HIBCPP show polar bacterial invasion only from the physiologically relevant basolateral side. Meningococcal invasion is attenuated by the presence of a capsule and translocated N. meningitidis form microcolonies on the apical side of HIBCPP opposite of sites of entry. As a functionally relevant human model of the BCSFB the HIBCPP offer a wide range of options for analysis of disease-related mechanisms at the choroid plexus epithelium, especially involving human pathogens.     

Brief Bursts Self-Inhibit and Correlate the Pyramidal Network

Inhibitory pathways are an essential component in the function of the neocortical microcircuitry. Despite the relatively small fraction of inhibitory neurons in the neocortex, these neurons are strongly activated due to their high connectivity rate and the intricate manner in which they interconnect with pyramidal cells (PCs). One prominent pathway is the frequency-dependent disynaptic inhibition (FDDI) formed between layer 5 PCs and mediated by Martinotti cells (MCs). Here, we show that simultaneous short bursts in four PCs are sufficient to exert FDDI in all neighboring PCs within the dimensions of a cortical column. This powerful inhibition is mediated by few interneurons, leading to strongly correlated membrane fluctuations and synchronous spiking between PCs simultaneously receiving FDDI. Somatic integration of such inhibition is independent and electrically isolated from monosynaptic excitation formed between the same PCs. FDDI is strongly shaped by I(h) in PC dendrites, which determines the effective integration time window for inhibitory and excitatory inputs. We propose a key disynaptic mechanism by which brief bursts generated by a few PCs can synchronize the activity in the pyramidal network.     

Dermatology: cutaneous manifestations of human immunodeficiency virus infection

The Scientific Board of the California Medical Association presents the following inventory of items of progress in dermatology. Each item, in the judgment of a panel of knowledgeable physicians, has recently become reasonably firmly established both as to scientific fact and important clinical significance. The items are presented in simple epitome and an authoritative reference, both to the item itself and to the subject as a whole, is generally given for those who may be unfamiliar with a particular item. The purpose is to assist busy practitioners, students, research workers, or scholars to stay abreast of these items of progress in dermatology that have recently achieved a substantial degree of authoritative acceptance, whether in their own field of special interest or another.The items of progress listed below were selected by the Advisory Panel to the Section on Dermatology of the California Medical Association, and the summaries were prepared under its direction.     

Kinetic β-deuterium isotope effects suggest a covalent mechanism for the protein folding enzyme peptidylprolyl cis/trans-isomerase

The cis/trans interconversion of Glt-Ala-Ala-Pro-Phe-4-nitroanilide and Glt-Ala-Gly-Pro-Phe-4-nitroanilide was studied both enzymatically and nonenzymatically by measuring kinetic β-deuterium isotope effects. The hydrogen atom at the α-carbon atom of the Xaa residue within the Xaa-Pro moiety was substituted by deuterium. In the nonenzymatic case the transition state of rotation is reflected by k_H/k_D > 1. When catalysed by 17 kDa PPIase the same bond rotation is characterized by k_H/k_D < 1. This suggests a covalent mechanism of catalysis which involves an approximately tetravalent carbon of the prolyl imidic bond for the transition state of reaction.     

Factors affecting the phytoaccumulation of weathered, soil-borne organic contaminants: analyses at the ex Planta and in Planta sides of the plant root

Persistent Organic Pollutants (POPs) in the soil–plant system were tracked from their origin in the bulk soil, into the rhizosphere soil pore water, to the xylem sap, and up to the aerial plant tissue. Specifically, the profiles of both chiral and achiral components of technical chlordane along this continuum were examined in detail for members of the Cucurbitaceae family: Cucurbita pepo L. subsp. pepo (“Black Beauty” true zucchini), Cucurbita pepo L. intersubspecific cross (“Zephyr” summer squash), and Cucumis sativus (“Marketmore” cucumber). The experiments were based on the use of mini-rhizotrons for collection and analysis of rhizosphere soil pore water for organic pollutants, as well as for low molecular weight organic acids (LMWOAs). In addition, the xylem sap and aerial plant tissue for intact, homografted, and heterografted C. pepo “Black Beauty” and C. sativus “Marketmore” plants were compared. The data indicate that profiles of the chlordane components in the pore water show no alteration in chiral patterns from those in the bulk soil and may be interpreted by physicochemical partitioning coefficients. Low molecular weight organic acids (LMWOAs) in the rhizosphere were observed to have a minor impact on bioavailability of the pollutants. However, once the pollutants cross the root membrane, major distinctive uptake and enantioselective patterns are apparent in the xylem sap, which are maintained in the aerial tissue. These in planta patterns are based on plant genotype. Specifically, grafting experiments with compatible heterografts of C. pepo and C. sativus establish that the chiral patterns are fully dependent on the plant root. The genotypic dependence of the data suggests possible mechanisms for phytoaccumulation.     

The female gametophyte and the endosperm control cell proliferation and differentiation of the seed coat in Arabidopsis

Double fertilization of the female gametophyte produces the endosperm and the embryo enclosed in the maternal seed coat. Proper seed communication necessitates exchanges of signals between the zygotic and maternal components of the seed. However, the nature of these interactions remains largely unknown. We show that double fertilization of the Arabidopsis thaliana female gametophyte rapidly triggers sustained cell proliferation in the seed coat. Cell proliferation and differentiation of the seed coat occur in autonomous seeds produced in the absence of fertilization of the multicopy suppressor of ira1 (msi1) mutant. As msi1 autonomous seeds mostly contain autonomous endosperm, our results indicate that the developing endosperm is sufficient to enhance cell proliferation and differentiation in the seed coat. We analyze the effect of autonomous proliferation in the retinoblastoma-related1 (rbr1) female gametophyte on seed coat development. In contrast with msi1, supernumerary nuclei in rbr1 female gametophytes originate mainly from the endosperm precursor lineage but do not express an endosperm fate marker. In addition, defects of the rbr1 female gametophyte also reduce cell proliferation in the ovule integuments before fertilization and prevent further differentiation of the seed coat. Our data suggest that coordinated development of the seed components relies on interactions before fertilization between the female gametophyte and the surrounding maternal ovule integuments and after fertilization between the endosperm and the seed coat.     

Colour-assortative mating among populations of Tropheus moorii, a cichlid fish from Lake Tanganyika, East Africa

The species flocks of cichlid fishes in the East African Lakes Tanganyika, Malawi and Victoria are prime examples of adaptive radiation and explosive speciation. Several hundreds of endemic species have evolved in each of the lakes over the past several thousands to a few millions years. Sexual selection via colour-assortative mating has often been proposed as a probable causal factor for initiating and maintaining reproductive isolation. Here, we report the consequences of human-mediated admixis among differentially coloured populations of the endemic cichlid fish Tropheus moorii from several localities that have accidentally been put in sympatry in a small harbour bay in the very south of Lake Tanganyika. We analysed the phenotypes (coloration) and genotypes (mitochondrial control region and five microsatellite loci) of almost 500 individuals, sampled over 3 consecutive years. Maximum-likelihood-based parenthood analyses and Bayesian inference of population structure revealed that significantly more juveniles are the product of within-colour-morph matings than could be expected under the assumption of random mating. Our results clearly indicate a marked degree of assortative mating with respect to the different colour morphs. Therefore, we postulate that sexual selection based on social interactions and female mate choice has played an important role in the formation and maintenance of the different colour morphs in Tropheus, and is probably common in other maternally mouthbrooding cichlids as well.     

MBD2 is required for correct spatial gene expression in the gut

Gene expression in the gut is segmentally regulated, but little is known of the molecular origin of patterning. Analysis of gene expression in colons from mice lacking the methyl-CpG binding repressor MBD2 revealed frequent activation of genes that are normally only expressed in the exocrine pancreas and duodenum. Reduced DNA methylation activated the same gene set in the colon. No significant differences in DNA methylation between the colon and duodenum were detected, but MBD2 was significantly more abundant in the colon. The relevance of MBD2 concentration was tested in a human colon cancer cell line. Depletion of MBD2 was again found to activate exocrine pancreatic genes. Gene activation in this cell culture model was accompanied by loss of promoter-bound MBD2 and increased histone acetylation. The results suggest that modulation of MBD2 during gut development establishes a region-specific gene expression pattern that is essential for establishing correct segmental character.