Ring1a/b polycomb proteins regulate the mesenchymal stem cell niche in continuously growing incisors

Rodent incisors are capable of growing continuously and the renewal of dental epithelium giving rise to enamel-forming ameloblasts and dental mesenchyme giving rise to dentin-forming odontoblasts and pulp cells is achieved by stem cells residing at their proximal ends. Although the dental epithelial stem cell niche (cervical loop) is well characterized, little is known about the dental mesenchymal stem cell niche. Ring1a/b are the core Polycomb repressive complex1 (PRC1) components that have recently also been found in a protein complex with BcoR (Bcl-6 interacting corepressor) and Fbxl10. During mouse incisor development, we found that genes encoding members of the PRC1 complex are strongly expressed in the incisor apical mesenchyme in an area that contains the cells with the highest proliferation rate in the tooth pulp, consistent with a location for transit amplifying cells. Analysis of Ring1a(-/-);Ring1b(cko/cko) mice showed that loss of Ring1a/b postnatally results in defective cervical loops and disturbances of enamel and dentin formation in continuously growing incisors. To further characterize the defect found in Ring1a(-/-);Ring1b(cko/cko) mice, we demonstrated that cell proliferation is dramatically reduced in the apical mesenchyme and cervical loop epithelium of Ring1a(-/-);Ring1b(cko/cko) incisors in comparison to Ring1a(-/-);Ring1b(fl/fl)cre- incisors. Fgf signaling and downstream targets that have been previously shown to be important in the maintenance of the dental epithelial stem cell compartment in the cervical loop are downregulated in Ring1a(-/-);Ring1b(cko/cko) incisors. In addition, expression of other genes of the PRC1 complex is also altered. We also identified an essential postnatal requirement for Ring1 proteins in molar root formation. These results show that the PRC1 complex regulates the transit amplifying cell compartment of the dental mesenchymal stem cell niche and cell differentiation in developing mouse incisors and is required for molar root formation.     

DEEP DIVERSIFICATION AND LONG‐TERM PERSISTENCE IN THE SOUTH AMERICAN ‘DRY DIAGONAL’: INTEGRATING CONTINENT‐WIDE PHYLOGEOGRAPHY AND DISTRIBUTION MODELING OF GECKOS

The relative influence of Neogene geomorphological events and Quaternary climatic changes as causal mechanisms on Neotropical diversification remains largely speculative, as most divergence timing inferences are based on a single locus and have limited taxonomic or geographic sampling. To investigate these influences, we use a multilocus (two mitochondrial and 11 nuclear genes) range‐wide sampling of Phyllopezus pollicaris, a gecko complex widely distributed across the poorly studied South American ‘dry diagonal’ biomes. Our approach couples traditional and model‐based phylogeography with geospatial methods, and demonstrates Miocene diversification and limited influence of Pleistocene climatic fluctuations on P. pollicaris. Phylogeographic structure and distribution models highlight that persistence across multiple isolated regions shaped the diversification of this species complex. Approximate Bayesian computation supports hypotheses of allopatric and ecological/sympatric speciation between lineages that largely coincide with genetic clusters associated with Chaco, Cerrado, and Caatinga, standing for complex diversification between the ‘dry diagonal’ biomes. We recover extremely high genetic diversity and suggest that eight well‐supported clades may be valid species, with direct implications for taxonomy and conservation assessments. These patterns exemplify how low‐vagility species complexes, characterized by strong genetic structure and pre‐Pleistocene divergence histories, represent ideal radiations to investigate broad biogeographic histories of associated biomes.     

The frpB1 gene of Helicobacter pylori is regulated by iron and encodes a membrane protein capable of binding haem and haemoglobin

FrpB1 is a novel membrane protein of Helicobacter pylori that is capable of binding both haem and haemoglobin but consistently shows more affinity for haem. The mRNA levels of frpB1 were repressed by iron and lightly modulated by haem or haemoglobin. The overexpression of the frpB1 gene supported cellular growth when haem or haemoglobin were supplied as the only iron source. Three-dimensional modelling revealed the presence of motifs necessary to bind either haem or haemoglobin. Our overall results support the idea that FrpB1 is a membrane protein of H. pylori that allows this pathogen to survive in the human stomach.     

Molecular dynamics simulation of GTPase activity in polymers of the cell division protein FtsZ

FtsZ, the prokaryotic ortholog of tubulin, assembles into polymers in the bacterial division ring. The interfaces between monomers contain a GTP molecule, but the relationship between polymerization and GTPase activity is not unequivocally proven. A set of short FtsZ polymers were modelled and the formation of active GTPase structures was monitored using molecular dynamics. Only the interfaces nearest the polymer ends exhibited an adequate geometry for GTP hydrolysis. Simulated conversion of interfaces from close-to-end to internal position and vice versa resulted in their spontaneous rearrangement between active and inactive conformations. This predicted behavior of FtsZ polymer ends was supported by in vitro experiments.     

Activation of the pyrin inflammasome by intracellular Burkholderia cenocepacia

Burkholderia cenocepacia is an opportunistic pathogen that causes chronic infection and induces progressive respiratory inflammation in cystic fibrosis patients. Recognition of bacteria by mononuclear cells generally results in the activation of caspase-1 and processing of IL-1β, a major proinflammatory cytokine. In this study, we report that human pyrin is required to detect intracellular B. cenocepacia leading to IL-1β processing and release. This inflammatory response involves the host adapter molecule ASC and the bacterial type VI secretion system (T6SS). Human monocytes and THP-1 cells stably expressing either small interfering RNA against pyrin or YFP-pyrin and ASC (YFP-ASC) were infected with B. cenocepacia and analyzed for inflammasome activation. B. cenocepacia efficiently activates the inflammasome and IL-1β release in monocytes and THP-1. Suppression of pyrin levels in monocytes and THP-1 cells reduced caspase-1 activation and IL-1β release in response to B. cenocepacia challenge. In contrast, overexpression of pyrin or ASC induced a robust IL-1β response to B. cenocepacia, which correlated with enhanced host cell death. Inflammasome activation was significantly reduced in cells infected with T6SS-defective mutants of B. cenocepacia, suggesting that the inflammatory reaction is likely induced by an as yet uncharacterized effector(s) of the T6SS. Together, we show for the first time, to our knowledge, that in human mononuclear cells infected with B. cenocepacia, pyrin associates with caspase-1 and ASC forming an inflammasome that upregulates mononuclear cell IL-1β processing and release.     

Discordant patterns of nuclear and mitochondrial introgression in Iberian populations of the European common frog (Rana temporaria)

Amphibians often show complex histories of intraspecific and interspecific genetic introgression, which might differ in mitochondrial and nuclear genes. In our study of the genetic differentiation of the European common frog, Rana temporaria (159 specimens from 23 populations were analyzed for 24 presumptive allozyme loci; 82 specimens were sequenced for a 540-bp fragment of the mitochondrial 16S rRNA gene), multilocus correspondence analysis (CA) and Bayesian assignment tests of the nuclear data were concordant in identifying 2 population groups corresponding to 1) the Pyrenees in the east and 2) the Galicia and Asturias regions in the west, the latter corresponding to the subspecies R. temporaria parvipalmata. Geographically intermediate populations were genetically intermediate in the allozyme CA and, less clearly in the Bayesian assignment, with mitochondrial haplotypes exclusively belonging to the parvipalmata group. This indicates different degrees of introgression in the mitochondrial and nuclear genomes. Although Pyrenean high-altitude populations are morphologically distinct from low-altitude populations, these 2 groups were not separate clusters in any analysis. This suggests that the morphological differences may be due to fast adaptation to elevational gradients, likely under maintenance of gene flow, and that the underlying genetic changes are not detectable by the analyzed markers. We argue that a parsimonious explanation for the observed pattern along the east-west axis in northern Spain may be competition between invading and resident populations, with no need to invoke selection. However, in order to conclusively rule out selective processes, additional and finer scale data are required to test for asymmetric mating preference/behaviour, sex-biased gene flow, or sex-biased survival of potential hybrids.     

The Prolyl Hydroxylase PHD3 Identifies Proinflammatory Macrophages and Its Expression Is Regulated by Activin A

Modulation of macrophage polarization underlies the onset and resolution of inflammatory processes, with polarization-specific molecules being actively sought as potential diagnostic and therapeutic tools. Based on their cytokine profile upon exposure to pathogenic stimuli, human monocyte-derived macrophages generated in the presence of GM-CSF or M-CSF are considered as proinflammatory (M1) or anti-inflammatory (M2) macrophages, respectively. We report in this study that the prolyl hydroxylase PHD3-encoding EGLN3 gene is specifically expressed by in vitro-generated proinflammatory M1(GM-CSF) human macrophages at the mRNA and protein level. Immunohistochemical analysis revealed the expression of PHD3 in CD163(+) lung macrophages under basal homeostatic conditions, whereas PHD3(+) macrophages were abundantly found in tissues undergoing inflammatory responses (e.g., Crohn's disease and ulcerative colitis) and in tumors. In the case of melanoma, PHD3 expression marked a subset of tumor-associated macrophages that exhibit a weak (e.g., CD163) or absent (e.g., FOLR2) expression of typical M2-polarization markers. EGLN3 gene expression in proinflammatory M1(GM-CSF) macrophages was found to be activin A dependent and could be prevented in the presence of an anti-activin A-blocking Ab or inhibitors of activin receptor-like kinase receptors. Moreover, EGLN3 gene expression was upregulated in response to hypoxia only in M2(M-CSF) macrophages, and the hypoxia-mediated upregulation of EGLN3 expression was significantly impaired by activin A neutralization. These results indicate that EGLN3 gene expression in macrophages is dependent on activin A both under basal and hypoxic conditions and that the expression of the EGLN3-encoded PHD3 prolyl hydroxylase identifies proinflammatory macrophages in vivo and in vitro.     

Analysis of a naturally-occurring deletion mutant of Spodoptera frugiperda multiple nucleopolyhedrovirus reveals sf58 as a new per os infectivity factor of lepidopteran-infecting baculoviruses

The Nicaraguan population of Spodoptera frugiperda multiple nucleopolyhedrovirus, SfMNPV-NIC, is structured as a mixture of nine genotypes (A-I). Occlusion bodies (OBs) of SfMNPV-C, -D and -G pure genotypes are incapable of oral transmission; a phenotype which in SfMNPV-C and -D is due to the absence of pif1 and pif2 genes. The complete sequence of the SfMNPV-G genome was determined to identify possible factors involved in this phenotype. Deletions of 4860 bp (22,366-27,225) and 60 bp (119,759-119,818) were observed in SfMNPV-G genome compared with that of the predominant complete genotype SfMNPV-B (132,954 bp). However no genes homologous to previously described per os infectivity factors were located within the deleted sequences. Significant differences were detected in the nucleotide sequence in sf58 gene (unknown function) that produced changes in the amino acid sequence and the predicted secondary structure of the corresponding protein. This gene is conserved only in lepidopteran baculoviruses (alpha- and betabaculoviruses). To determine the role of sf58 in peroral infectivity a deletion mutant was constructed using bacmid technology. OBs of the deletion mutant (Sf58null) were not orally infectious for S. frugiperda larvae, whereas Sf58null rescue virus OBs recovered oral infectivity. Sf58null DNA and occlusion derived virions (ODVs) were as infective as SfMNPV bacmid DNA and ODVs in intrahemocelically infected larvae or cell culture, indicating that defects in ODV or OB morphogenesis were not involved in the loss of peroral infectivity. Addition of optical brightener or the presence of the orally infectious SfMNPV-B OBs in mixtures with SfMNPV-G OBs did not recover Sf58null OB infectivity. According to these results sf58 is a new per os infectivity factor present only in lepidopteran baculoviruses.