根据外部形态特征试论披碱草属3组植物间的系统关系

通过对披碱草属中小颖组、宽颖组和长颖组种类外部形态的观察,总结了3组植物外部形态特征的异同,探讨了形态学特征的分类学意义。同时,根据3组植物外部形态性状—花序、小穗、小花、以及内稃的演化趋势,分析了各组的演化关系和系统位置。结果表明：小颖组最原始,宽颖组较进化,长颖组最高级;小颖组可能直接派生了较进化的宽颖组,并在宽颖组的基础上进而产生了最高级的长颖组。此外,本文对披碱草属参试种的系统关系也作了一定程度的探讨,结果显示圆锥披碱草最原始,墨西哥披碱草最进化,其余参试种居于两者之间。上述研究工作为整个披碱草属系统与进化方面的探讨提供了形态学方面的理论证据。     

Transglutaminase 2 ablation leads to defective function of mitochondrial respiratory complex I affecting neuronal vulnerability in experimental models of extrapyramidal disorders

Transglutaminase 2 (TG2) represents the most ubiquitous isoform belonging to the TG family, and has been implicated in the pathophysiology of basal ganglia disorders, such as Parkinson's disease and Huntington's disease. We show that ablation of TG2 in knockout mice causes a reduced activity of mitochondrial complex I associated with an increased activity of complex II in the whole forebrain and striatum. Interestingly, TG2-/- mice were protected against nigrostriatal damage induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, which is converted in vivo into the mitochondrial complex I inhibitor, 1-methyl-4-phenyl-pyridinium ion. In contrast, TG2-/- mice were more vulnerable to nigrostriatal damage induced by methamphetamine or by the complex II inhibitor, 3-nitropropionic acid. Proteomic analysis showed that proteins involved in the mitochondrial respiratory chain, such as prohibitin and the beta-chain of ATP synthase, are substrates for TG2. These data suggest that TG2 is involved in the regulation of the respiratory chain both in physiology and pathology, contributing to set the threshold for neuronal damage in extrapyramidal disorders.     

Interaction of the alternating double stranded copolymer poly(dA-dT) x poly(dA-dT) with NiCl(2) and CdCl(2): solution behavior

The thermal denaturation of the synthetic high molecular weight double stranded polynucleotide poly(dA-dT) x poly(dA-dT) has been studied in aqueous buffered solution (Tris 1.0 mM; pH 7.8+/-0.2) in the presence of increasing concentrations of either Ni(2+) (borderline cation) or Cd(2+) (soft cation) at four different constant ionic strength values (NaCl), making use of UV and circular dichroism (CD) spectroscopies. The experimental results show that the B-type double helix of the polymer is stabilized against thermal denaturation in the presence of both cations at low concentrations, relative to the systems where only NaCl is present, in the same conditions of ionic strength and pH. The effect is more pronounced for Ni(2+) than for Cd(2+). At higher concentrations, both cations start to destabilize the double helix, with Cd cations inducing larger variations of T(m). In many cases, when denaturation starts, interstrand cross-linking occurs with formation of aggregates that precipitate.     

Pharmacological targeting of p53 through RITA is an effective antitumoral strategy for malignant pleural mesothelioma

Malignant mesothelioma, a very aggressive tumor associated to asbestos exposure, is expected to increase in incidence, and unfortunately, no curative modality exists. Reactivation of p53 is a new attractive antitumoral strategy. p53 is rarely mutated in mesothelioma, but it is inactivated in most tumors by the lack of p14^ARF. Here, we evaluated the feasibility of this approach in pleural mesothelioma by testing RITA and nutlin-3, two molecules able to restore p53 function through a different mechanism, on a panel of mesothelioma cell lines representing the epithelioid (NCI-H28, NCI-H2452, IST-MES 2), biphasic (MSTO-211H), and sarcomatoid (NCI-H2052) histotypes compared with the normal mesothelial HMC-hTERT. RITA triggered robust caspase-dependent apoptosis specifically in epithelioid and biphasic mesothelioma cell lines, both through wild-type and mutant p53, concomitant to p21 downregulation. Conversely, nutlin-3 induced a p21-dependent growth arrest, rather than apoptosis, and was slightly toxic on HMC-hTERT.

Interestingly, we identified a previously undetected point mutation of p53 (p.Arg249Ser) in IST-MES 2, and showed that RITA is also able to reactivate this p53 mutant protein and its apoptotic function. RITA reduced tumor growth in a MSTO-211H-derived xenograft model of mesothelioma and synergized with cisplatin, which is the mainstay of treatment for this tumor.

Our data indicate that reactivation of p53 and concomitant p21 downregulation effectively induce cell death in mesothelioma, a tumor characterized by a high intrinsic resistance to apoptosis. Altogether, our findings provide the preclinical framework supporting the use of p53-reactivating agents alone, or in combination regimens, to improve the outcome of patients with mesothelioma.     

Toll-Like Receptor 8 Agonist and Bacteria Trigger Potent Activation of Innate Immune Cells in Human Liver

The ability of innate immune cells to sense and respond to impending danger varies by anatomical location. The liver is considered tolerogenic but is still capable of mounting a successful immune response to clear various infections. To understand whether hepatic immune cells tune their response to different infectious challenges, we probed mononuclear cells purified from human healthy and diseased livers with distinct pathogen-associated molecules. We discovered that only the TLR8 agonist ssRNA40 selectively activated liver-resident innate immune cells to produce substantial quantities of IFN-γ. We identified CD161^Bright mucosal-associated invariant T (MAIT) and CD56^Bright NK cells as the responding liver-resident innate immune cells. Their activation was not directly induced by the TLR8 agonist but was dependent on IL-12 and IL-18 production by ssRNA40-activated intrahepatic monocytes. Importantly, the ssRNA40-induced cytokine-dependent activation of MAIT cells mirrored responses induced by bacteria, i.e., generating a selective production of high levels of IFN-γ, without the concomitant production of TNF-α or IL-17A. The intrahepatic IFN-γ production could be detected not only in healthy livers, but also in HBV- or HCV-infected livers. In conclusion, the human liver harbors a network of immune cells able to modulate their immunological responses to different pathogen-associated molecules. Their ability to generate a strong production of IFN-γ upon stimulation with TLR8 agonist opens new therapeutic opportunities for the treatment of diverse liver pathologies.     

Class I Major Histocompatibility Complex,the Trojan Horse for Secretion of Amyloidogenic β2-Microglobulin

To form extracellular aggregates, amyloidogenic proteins bypass the intracellular quality control, which normally targets unfolded/aggregated polypeptides. Human D76N β₂-microglobulin (β₂m) variant is the prototype of unstable and amyloidogenic protein that forms abundant extracellular fibrillar deposits. Here we focus on the role of the class I major histocompatibility complex (MHCI) in the intracellular stabilization of D76N β₂m. Using biophysical and structural approaches, we show that the MHCI containing D76N β₂m (MHCI₇₆) displays stability, dissociation patterns, and crystal structure comparable with those of the MHCI with wild type β₂m. Conversely, limited proteolysis experiments show a reduced protease susceptibility for D76N β₂m within the MHCI₇₆ as compared with the free variant, suggesting that the MHCI has a chaperone-like activity in preventing D76N β₂m degradation within the cell. Accordingly, D76N β₂m is normally assembled in the MHCI and circulates as free plasma species in a transgenic mouse model.     

The Human SLC25A33 and SLC25A36 Genes of Solute Carrier Family 25 Encode Two Mitochondrial Pyrimidine Nucleotide Transporters

The human genome encodes 53 members of the solute carrier family 25 (SLC25), also called the mitochondrial carrier family, many of which have been shown to transport inorganic anions, amino acids, carboxylates, nucleotides, and coenzymes across the inner mitochondrial membrane, thereby connecting cytosolic and matrix functions. Here two members of this family, SLC25A33 and SLC25A36, have been thoroughly characterized biochemically. These proteins were overexpressed in bacteria and reconstituted in phospholipid vesicles. Their transport properties and kinetic parameters demonstrate that SLC25A33 transports uracil, thymine, and cytosine (deoxy)nucleoside di- and triphosphates by an antiport mechanism and SLC25A36 cytosine and uracil (deoxy)nucleoside mono-, di-, and triphosphates by uniport and antiport. Both carriers also transported guanine but not adenine (deoxy)nucleotides. Transport catalyzed by both carriers was saturable and inhibited by mercurial compounds and other inhibitors of mitochondrial carriers to various degrees. In confirmation of their identity (i) SLC25A33 and SLC25A36 were found to be targeted to mitochondria and (ii) the phenotypes of Saccharomyces cerevisiae cells lacking RIM2, the gene encoding the well characterized yeast mitochondrial pyrimidine nucleotide carrier, were overcome by expressing SLC25A33 or SLC25A36 in these cells. The main physiological role of SLC25A33 and SLC25A36 is to import/export pyrimidine nucleotides into and from mitochondria, i.e. to accomplish transport steps essential for mitochondrial DNA and RNA synthesis and breakdown.