HYBRIDOGENESIS AND ANDROGENESIS IN THE STICK-INSECT BACILLUS ROSSIUS-GRANDII BENAZZII (INSECTA,PHASMATODEA)

In northwestern Sicily interspecific hybrid females between Bacillus rossius and B. grandii benazzii (Insecta, Phasmatodea) are sympatric with facultatively parthenogenetic demes of the former and bisexual populations of the latter. Preliminary observations suggested that hybrid females are maintained by hybridogenetic reproduction, not by current F₁ hybrid production nor through parthenogenesis. Being hybridogens, a complex of hemiclonal lineages, we informally refer to them as B. rossius-grandii benazzii, according to Schultz's proposal. In this study B. rossius-g. benazzii females were crossed with males of B. g. benazzii, B. g. grandii, B. g. maretimi, and B. rossius. Allozyme analysis of the progeny showed that the great majority of them were actually produced by hybridogenesis with a hemiclonal inheritance of the maternal B. rossius genotype (Br^m) and actual syngamy with a sperm from the fathering male, so that Br^m-gb^p, Br^m-gg^p, Br^m-gm^p, and Br^m-r^p offspring were obtained in the respective crosses. All-paternal progeny (androgenetics) were also produced (Bgb^pgb^p, Bgm^pgm^p, Br^pr^p) and two gynogenetic descendants were observed. Cytological investigations on virgin eggs that failed to hatch revealed in most of them a haploid-diploid blocked blastoderm; this rudimentary parthenogenesis appears to be an important prerequisite for further evolution of this hybridogen. Reproductive modes of descendants were also analyzed; although Br^m-g^p hybrids are still able to reproduce by hybridogenesis, a progressive disruption of the hybridogenetic-androgenetic system takes place in synthetic B. rossius (Br^m-r^p, Br^pr^p) and abundant thelytokous parthenogenetic offspring are obtained from females of androgenetic origin. The evolutionary role of these hybridogens appears to be linked to their shift towards parthenogenesis; this has apparently occurred in the southeastern Sicilian hybrid B. whitei (=B. rossius/g. grandii), which exhibits both hybridogenesis and parthenogenesis.     

Role of Ca2+ in the electrostatic stability and the functional activity of the globular domain of human C1q

C1q is the recognition subunit of the classical pathway of the complement system and a major connecting link between classical pathway-driven innate immunity and IgG- or IgM-mediated acquired immunity. The basic structural subunit of C1q is composed of an N-terminal triple-helical collagen-like region and a C-terminal heterotrimeric globular head domain (gC1q) that is made up of individual A, B, and C chains. Recent crystallographic studies have revealed that the gC1q domain, which is the main target-binding region of C1q, has a compact and spherical heterotrimeric assembly, held together by both electrostatic and nonpolar interactions, with quasi-3-fold symmetry. A characteristic feature of the gC1q domain is the presence of a exposed Ca(2+) located near the apex. We have investigated, using theoretical and experimental approaches, the role of Ca(2+) in the electrostatic stability and target-binding properties of the native C1q as well as recombinant monomeric forms of the C-terminal regions of the A, B, and C chains. Here, we report that Ca(2+) primarily influences the target recognition properties of C1q toward IgG, IgM, C-reactive protein, and pentraxin 3. At pH 7.4, the loss of Ca(2+) leads to changes in the direction of electric moment from coaxial (where the putative C-reactive protein-binding site is located) to perpendicular to the molecular axis (toward the most likely IgG-binding site), which appears important for target recognition by C1q and subsequent complement activation.     

Wolbachia infection in the newly described Ecuadorian sand flea, Tunga trimamillata

Wolbachia pipientis is an intracellular endosymbiont producing reproductive alterations in its hosts. This bacterium have been reported in many arthropods and nematodes. By PCR amplification and sequencing of the 16S rDNA and ftsZ genes we have identified a Wolbachia strain in the newly described sand-flea, Tunga trimamillata. Prevalence of this endosymbiont in the 26 individuals screened is equal to 35%. Sympatric and allopatric specimens of the related species Tunga penetrans were also analysed, but in contrast to literature data, Wolbachia appears absent in the presently analysed 24 specimens. Field studies evidence a female-biased sex-ratio in T. trimamillata, suggesting that Wolbachia may cause sex-ratio distortion in this species. By means of BLAST search and phylogenetic analysis we found that the Wolbachia strain from T. trimamillata pertains to the arthropod-infecting Wolbachia; this strain is highly differentiated from the Wolbachia strain of T. penetrans described in literature.     

beta-Arrestin-dependent constitutive internalization of the human chemokine decoy receptor D6

Seven transmembrane receptors mediate diverse physiological responses including hormone action, olfaction, neurotransmission, and chemotaxis. Human D6 is a non-signaling seven-transmembrane receptor expressed on lymphatic endothelium interacting with most inflammatory CC-chemokines resulting in their rapid internalization. Here, we demonstrate that this scavenging activity is mediated by continuous internalization and constant surface expression of the receptor, a process involving the clathrin-coated pit-dependent pathway. D6 constitutively associates with the cytoplasmic adaptor beta-arrestin, and this interaction is essential for D6 internalization. An acidic region, but not the putative phosphorylation sites in the cytoplasmic tail of D6, is critical for receptor interaction with beta-arrestin and subsequent internalization. Neither the native D6 nor mutants uncoupled from beta-arrestin activate any G-protein-mediated signaling pathways. Therefore, D6 may be considered a decoy receptor structurally adapted to perform chemokine scavenging.     

The Angiogenic Inhibitor Long Pentraxin PTX3 Forms an Asymmetric Octamer with Two Binding Sites for FGF2

The inflammation-associated long pentraxin PTX3 plays key roles in innate immunity, female fertility, and vascular biology (e.g. it inhibits FGF2 (fibroblast growth factor 2)-mediated angiogenesis). PTX3 is composed of multiple protomers, each composed of distinct N- and C-terminal domains; however, it is not known how these are organized or contribute to its functional properties. Here, biophysical analyses reveal that PTX3 is composed of eight identical protomers, associated through disulfide bonds, forming an elongated and asymmetric, molecule with two differently sized domains interconnected by a stalk. The N-terminal region of the protomer provides the main structural determinant underlying this quaternary organization, supporting formation of a disulfide-linked tetramer and a dimer of dimers (a non-covalent tetramer), giving rise to the asymmetry of the molecule. Furthermore, the PTX3 octamer is shown to contain two FGF2 binding sites, where it is the tetramers that act as the functional units in ligand recognition. Thus, these studies provide a unifying model of the PTX3 oligomer, explaining both its quaternary organization and how this is required for its antiangiogenic function.     

Liver parenchyma heterogeneity in the response to extracellular NAD+

The perfused rat liver responds intensely to NAD+ infusion (20-100 microM). Increases in portal perfusion pressure and glycogenolysis and transient inhibition of oxygen consumption are some of the effects that were observed. The aim of the present work was to investigate the distribution of the response to extracellular NAD+ along the hepatic acinus. The bivascularly perfused rat liver was used. Various combinations of perfusion directions (antegrade and retrograde) and infusion routes (portal vein, hepatic vein and hepatic artery) were used in order to supply NAD+ to different regions of the liver parenchyma, also taking advantage of the fact that its extracellular transformation generates steep concentration gradients. Oxygen uptake was stimulated by NAD+ in retrograde perfusion (irrespective of the infusion route) and transiently inhibited in antegrade perfusion. This indicates that the signal causing oxygen uptake inhibition is generated in the periportal area. The signal responsible for oxygen uptake stimulation is homogenously distributed. Stimulation of glucose release was more intense when NAD+ was infused into the portal vein or into the hepatic artery, indicating that stimulation of glycogenolysis predominates in the periportal area. The increases in perfusion pressure were more pronounced when the periportal area was supplied with NAD+ suggesting that the vasoconstrictive elements responding to NAD+ predominate in this region. The response to extracellular NAD+ is thus unequally distributed in the liver. As a paracrine agent, NAD+ is likely to be released locally. It can be concluded that its effects will be different depending on the area where it is released.     

The action of extracellular NAD+ on gluconeogenesis in the perfused rat liver

In the rat liver NAD⁺ infusion produces increases in portal perfusion pressure and glycogenolysis and transient inhibition of oxygen consumption. The aim of the present work was to investigate the possible action of this agent on gluconeogenesis using lactate as a gluconeogenic precursor. Hemoglobin-free rat liver perfusion in antegrade and retrograde modes was used with enzymatic determination of glucose production and polarographic assay of oxygen uptake. NAD⁺ infusion into the portal vein (antegrade perfusion) produced a concentration-dependent (25–100 μM) transient inhibition of oxygen uptake and gluconeogenesis. For both parameters inhibition was followed by stimulation. NAD⁺ infusion into the hepatic vein (retrograde perfusion) produced only transient stimulations. During Ca²⁺-free perfusion the action of NAD⁺ was restricted to small transient stimulations. Inhibitors of eicosanoid synthesis with different specificities (indo-methacin, nordihydroguaiaretic acid, bromophenacyl bromide) either inhibited or changed the action of NAD⁺. The action of NAD⁺ on gluconeogenesis is probably mediated by eicosanoids synthesized in non-parenchymal cells. As in the fed state, in the fasted condition extracellular NAD⁺ is also able to exert two opposite effects, inhibition and stimulation. Since inhibition did not manifest significantly in retrograde perfusion it is likely that the generating signal is located in pre-sinusoidal regions.     

Tuning inflammation and immunity by chemokine sequestration: decoys and more

A set of chemokine receptors are structurally unable to elicit migration or conventional signalling responses after ligand engagement. These 'silent' (non-signalling) chemokine receptors regulate inflammatory and immune reactions in different ways, including by acting as decoys and scavengers. Chemokine decoy receptors recognize distinct and complementary sets of ligands and are strategically expressed in different cellular contexts. Importantly, viruses and parasites have evolved multiple strategies to elude chemokines, including the expression of decoy receptors. So, decoy receptors for chemokines represent a general strategy to tune, shape and temper innate and adaptive immunity.