Fruits of Heterocoma (Vernonieae‐Lychnophorinae): taxonomic significance and a new pattern of phytomelanin deposition in Asteraceae

Heterocoma is a Brazilian endemic genus resulting from the dismemberment of Sipolisiinae, in which only representatives with fruit containing phytomelanin were included in the genus. As the fruits of Asteraceae are known to be systematically important at various taxonomic levels and Heterocoma fruit has not been described previously, we studied the morphology and anatomy of the cypselas of all species of the genus, comparing them with other fruits in the family containing phytomelanin and evaluating the systematic potential at the specific and tribal levels. The fruits were analysed by scanning electron microscopy (SEM) and light microscopy. The morphological features of the fruit, including the carpopodium, ribs and pappi, varied in the genus and demonstrated potential for species discrimination. The anatomy showed a pattern for the genus with a uniseriate exocarp, the outer mesocarp composed of fibres arranged in several layers, the inner mesocarp composed of several layers of parenchyma, the endocarp, and phytomelanin deposited between the inner and outer mesocarp. This anatomical pattern of phytomelanin deposition differs from that of other Asteraceae with phytomelanin in their fruit. Heterocoma is also the only genus in Vernonieae that has phytomelanin deposition in the cypselas. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 179 , 255–265.     

Xylanase production by endophytic Aspergillus niger using pentose-rich hydrothermal liquor from sugarcane bagasse

Fungal xylanases have been widely studied and various production methods have been proposed using submerged and solid-state fermentation. This class of enzyme is used to supplement cellulolytic enzyme cocktails in order to enhance the enzymatic hydrolysis of plant cell walls. The present work investigates the production of xylanase and other accessory enzymes by a recently isolated endophytic Aspergillus niger DR02 strain, using the pentose-rich liquor from hydrothermal pretreatment of sugarcane bagasse as carbon source. Batch and fed-batch submerged cultivation approaches were developed in order to minimize the toxicity of the liquor and increase enzyme production. Maximum xylanase activities obtained were 458.1 U/mL for constant fed-batch, 428.1 U/mL for exponential fed-batch, and 264.37 U/mL for pulsed fed-batch modes. The results indicated that carbon-limited fed-batch cultivation can reduce fungal catabolite repression, as well as overcome possible negative effects of toxic compounds present in the pentose-rich liquor. Enzymatic panel and mass spectrometric analyses of the fed-batch A. niger secretome showed high levels of xylanolytic enzymes (GH10, GH11, and GH62 Cazy families), together with cellobiohydrolase (G6 and GH7), β-glucosidase, β-xylosidase (GH3), and feruloyl esterase (CE1) accessory enzyme activities. The yields of glucose and xylose from enzymatic hydrolysis of hydrothermally pretreated sugarcane bagasse increased by 43.7 and 65.3%, respectively, when a commercial cellulase preparation was supplemented with the A. niger DR02 constant fed-batch enzyme complex.     

Structural Insights on Two Hypothetical Secretion Chaperones from <Emphasis Type="Italic">Xanthomonas axonopodis</Emphasis> pv<Emphasis Type="Italic">. citri</Emphasis>

Several Gram-negative bacterial pathogens have developed type III secretion systems (T3SSs) to deliver virulence proteins directly into eukaryotic cells in a process essential for many diseases. The type III secretion processes require customized chaperones with high specificity for binding partners, thus providing the secretion to occur. Due to the very low sequence similarities among secretion chaperones, annotation and discrimination of a great majority of them is extremely difficult and a task with low scores even if genes are encountered that codify for small (<20 kDa) proteins with low pI and a tendency to dimerise. Concerning about this, herein, we present structural features on two hypothetical T3SSs chaperones belonging to plant pathogen Xanthomonas axonopodis pv. citri and suggest how low resolution models based on Small Angle X-ray Scattering patterns can provide new structural insights that could be very helpful in their analysis and posterior classification.     

UBE4B promotes Hdm2-mediated degradation of the tumor suppressor p53

The TP53 gene (encoding the p53 tumor suppressor) is rarely mutated, although frequently inactivated, in medulloblastoma and ependymoma. Recent work in mouse models showed that the loss of p53 accelerated the development of medulloblastoma. The mechanism underlying p53 inactivation in human brain tumors is not completely understood. We show that ubiquitination factor E4B (UBE4B), an E3 and E4 ubiquitin ligase, physically interacts with p53 and Hdm2 (also known as Mdm2 in mice). UBE4B promotes p53 polyubiquitination and degradation and inhibits p53-dependent transactivation and apoptosis. Notably, silencing UBE4B expression impairs xenotransplanted tumor growth in a p53-dependent manner and overexpression of UBE4B correlates with decreased expression of p53 in these tumors. We also show that UBE4B overexpression is often associated with amplification of its gene in human brain tumors. Our data indicate that amplification and overexpression of UBE4B represent previously undescribed molecular mechanisms of inactivation of p53 in brain tumors.     

Vitamin A: a multifunctional tool for development

Extensive research carried out over the last 100 years has established that the fat-soluble organic compound vitamin A plays crucial roles in early development, organogenesis, cell proliferation, differentiation and apoptosis as well as in tissue homeostasis. Given its importance during development, the delivery of vitamin A to the embryo is very tightly regulated with perturbations leading to severe malformations. This review discusses the roles of vitamin A during human development and the molecular mechanisms controlling its biological effects, hence bridging the gap between human development and molecular genetic work carried out in animal models. Vitamin A delivery during pregnancy and its developmental teratology in humans are thus discussed alongside work on model organisms, such as chicken or mice, revealing the molecular layout and functions of vitamin A metabolism and signaling. We conclude that, during development, vitamin A-derived signals are very tightly controlled in time and space and that this complex regulation is achieved by elaborate autoregulatory loops and by sophisticated interactions with other signaling cascades.     

Brucella abortus inhibits IFN-γ-induced FcγRI expression and FcγRI-restricted phagocytosis via toll-like receptor 2 on human monocytes/macrophages

The strategies that allow Brucella abortus to persist for years inside macrophages subverting host immune responses are not completely understood. Immunity against this bacterium relies on the capacity of IFN-γ to activate macrophages, endowing them with the ability to destroy intracellular bacteria. We report here that infection with B. abortus down-modulates the expression of the type I receptor for the Fc portion of IgG (FcγRI, CD64) and FcγRI-restricted phagocytosis regulated by IFN-γ in human monocytes/macrophages. Both phenomena were not dependent on bacterial viability, since they were also induced by heat-killed B. abortus (HKBA), suggesting that they were elicited by a structural bacterial component. Accordingly, a prototypical B. abortus lipoprotein (L-Omp19), but not its unlipidated form, inhibited both CD64 expression and FcγRI-restricted phagocytosis regulated by IFN-γ. Moreover, a synthetic lipohexapeptide that mimics the structure of the protein lipid moiety also inhibited CD64 expression, indicating that any Brucella lipoprotein could down-modulate CD64 expression and FcγRI-restricted phagocytosis. Pre-incubation of monocytes/macrophages with anti-TLR2 mAb blocked the inhibition of the CD64 expression mediated by HKBA and L-Omp19. These results, together with our previous observations establish that B. abortus utilizes its lipoproteins to inhibit the monocytes/macrophages activation mediated by IFN-γ and to subvert host immunonological responses.     

Assessment of the genetic risks of a metallic alloy used in medical implants

The use of artificial implants provides a palliative or permanent solution for individuals who have lost some bodily function through disease, an accident or natural wear. This functional loss can be compensated for by the use of medical devices produced from special biomaterials. Titanium alloy (Ti-6Al-4V) is a well-established primary metallic biomaterial for orthopedic implants, but the toxicity of the chemical components of this alloy has become an issue of concern. In this work, we used the MTT assay and micronucleus assay to examine the cytotoxicity and genotoxicity, respectively, of an extract obtained from this alloy. The MTT assay indicated that the mitochondrial activity and cell viability of CHO-K1 cells were unaffected by exposure to the extract. However, the micronucleus assay revealed DNA damage and an increase in micronucleus frequency at all of the concentrations tested. These results show that ions released from Ti-6Al-4V alloy can cause DNA and nuclear damage and reinforce the importance of assessing the safety of metallic medical devices constructed from biomaterials.