Mark J. Schneider

Cloning of a cDNA for the Type II Iodothyronine Deiodinase

Three types of iodothyronine deiodinase have been identified in vertebrate tissues. cDNAs for the types I and III have been cloned and shown to contain an in-frame TGA that codes for selenocysteine at the active site of the enzyme. We now report the cloning of a cDNA for a type II deiodinase using a reverse transcription/polymerase chain reaction strategy and RNA obtained from Rana catesbeiana tissues. This cDNA (RC5′DII) manifests limited but significant homology with other deiodinase cDNAs and contains a conserved in-frame TGA codon. Injection of capped in vitro synthesized transcripts of the cDNA into Xenopuslaevis oocytes results in the induction of deiodinase activity with characteristics typical of a type II deiodinase. The levels of RC5′DII transcripts in R. catesbeiana tadpole tail and liver mRNA at stages XII and XXIII correspond well with that of type II deiodinase activity but not that of the type III activity in these tissues. These findings indicate that the amphibian type II 5′-deiodinase is a structurally unique member of the family of selenocysteine-containing deiodinases.

A Protein Methylation Pathway in Chlamydomonas Flagella Is Active during Flagellar Resorption

During intraflagellar transport (IFT), the regulation of motor proteins, the loading and unloading of cargo and the turnover of flagellar proteins all occur at the flagellar tip. To begin an analysis of the protein composition of the flagellar tip, we used difference gel electrophoresis to compare long versus short (i.e., regenerating) flagella. The concentration of tip proteins should be higher relative to that of tubulin (which is constant per unit length of the flagellum) in short compared with long flagella. One protein we have identified is the cobalamin-independent form of methionine synthase (MetE). Antibodies to MetE label flagella in a punctate pattern reminiscent of IFT particle staining, and immunoblot analysis reveals that the amount of MetE in flagella is low in full-length flagella, increased in regenerating flagella, and highest in resorbing flagella. Four methylated proteins have been identified in resorbing flagella, using antibodies specific for asymmetrically dimethylated arginine residues. These proteins are found almost exclusively in the axonemal fraction, and the methylated forms of these proteins are essentially absent in full-length and regenerating flagella. Because most cells resorb cilia/flagella before cell division, these data indicate a link between flagellar protein methylation and progression through the cell cycle.

Tissue-Protective Effects of NKG2A in Immune-Mediated Clearance of Virus Infection

Virus infection triggers a CD8+ T cell response that aids in virus clearance, but also expresses effector functions that may result in tissue injury. CD8+ T cells express a variety of activating and inhibiting ligands, though regulation of the expression of inhibitory receptors is not well understood. The ligand for the inhibitory receptor, NKG2A, is the non-classical MHC-I molecule Qa1b, which may also serve as a putative restricting element for the T cell receptors of purported regulatory CD8+ T cells. We have previously shown that Qa1b-null mice suffer considerably enhanced immunopathologic lung injury in the context of CD8+ T cell-mediated clearance of influenza infection, as well as evidence in a non-viral system that failure to ligate NKG2A on CD8+ effector T cells may represent an important component of this process. In this report, we examine the requirements for induction of NKG2A expression, and show that NKG2A expression by CD8+ T cells occurs as a result of migration from the MLN to the inflammatory lung environment, irrespective of peripheral antigen recognition. Further, we confirmed that NKG2A is a mediator in limiting immunopathology in virus infection using mice with a targeted deletion of NKG2A, and infecting the mutants with two different viruses, influenza and adenovirus. In neither infection is virus clearance altered. In influenza infection, the enhanced lung injury was associated with increased chemoattractant production, increased infiltration of inflammatory cells, and significantly enhanced alveolar hemorrhage. The primary mechanism of enhanced injury was the loss of negative regulation of CD8+ T cell effector function. A similar effect was observed in the livers of mutant mice infected intravenously with adenovirus. These results demonstrate the immunoregulatory role of CD8+ NKG2A expression in virus infection, which negatively regulates T cell effector functions and contributes to protection of tissue integrity during virus clearance.

Volatile fingerprinting of human respiratory viruses from cell culture

Abstract Volatile metabolites are currently under investigation as potential biomarkers for the detection and identification of pathogenic microorganisms, including bacteria, fungi, and viruses. Unlike bacteria and fungi, which produce distinct volatile metabolic signatures associated with innate differences in both primary and secondary metabolic processes, viruses are wholly reliant on the metabolic machinery of infected cells for replication and propagation. In the present study, the ability of volatile metabolites to discriminate between respiratory cells infected and uninfected with virus, in vitro, was investigated. Two important respiratory viruses, namely respiratory syncytial virus (RSV) and influenza A virus (IAV), were evaluated. Data were analyzed using three different machine learning algorithms (random forest (RF), linear support vector machines (linear SVM), and partial least squares-discriminant analysis (PLS-DA)), with volatile metabolites identified from a training set used to predict sample classifications in a validation set. The discriminatory performances of RF, linear SVM, and PLS-DA were comparable for the comparison of IAV-infected versus uninfected cells, with area under the receiver operating characteristic curves (AUROCs) between 0.78 and 0.82, while RF and linear SVM demonstrated superior performance in the classification of RSV-infected versus uninfected cells (AUROCs between 0.80 and 0.84) relative to PLS-DA (0.61). A subset of discriminatory features were assigned putative compound identifications, with an overabundance of hydrocarbons observed in both RSV- and IAV-infected cell cultures relative to uninfected controls. This finding is consistent with increased oxidative stress, a process associated with viral infection of respiratory cells.