Molecular Characterization of the Mouse Tyrosinase Gene:Pigment Cell-Specific Expression in Transgenic Mice

Tyrosinase is the key enzyme in melanin synthesis, and is expressed in the pigment epithelium of the retina, a cell layer derived from the optic cup; and in neural crest-derived melanocytes of skin, hair follicle, choroid, and iris. The tyrosinase gene has been cloned and shown to map to the well-characterized c-locus (albino locus) of the mouse. Subsequent studies demonstrated that a functional tyrosinase minigene was able to rescue the albino phenotype in transgenic mice. The transgene was expressed in a cell type-specific manner in skin and eye. During development of the mouse, the tyrosinase gene is expressed in the pigment epithelium of the retina as early as day 10.5 of gestation. In the hair follicle, tyrosinase gene expression is detected from day 16.5 onwards. This cell-type–specific expression is largely reproduced in transgenic mice. Our results suggest that sequences in the immediate vicinity of the mouse tyrosinase gene are sufficient to provide cell type-specificity and developmental regulation in melanocytes and the pigment epithelium.     

When History Repeats Itself: Exploring the Genetic Architecture of Host-Plant Adaptation in Two Closely Related Lepidopteran Species

The genus Ostrinia includes two allopatric maize pests across Eurasia, namely the European corn borer (ECB, O. nubilalis) and the Asian corn borer (ACB, O. furnacalis). A third species, the Adzuki bean borer (ABB, O. scapulalis), occurs in sympatry with both the ECB and the ACB. The ABB mostly feeds on native dicots, which probably correspond to the ancestral host plant type for the genus Ostrinia. This situation offers the opportunity to characterize the two presumably independent adaptations or preadaptations to maize that occurred in the ECB and ACB. In the present study, we aimed at deciphering the genetic architecture of these two adaptations to maize, a monocot host plant recently introduced into Eurasia. To this end, we performed a genome scan analysis based on 684 AFLP markers in 12 populations of ECB, ACB and ABB. We detected 2 outlier AFLP loci when comparing French populations of the ECB and ABB, and 9 outliers when comparing Chinese populations of the ACB and ABB. These outliers were different in both countries, and we found no evidence of linkage disequilibrium between any two of them. These results suggest that adaptation or preadaptation to maize relies on a different genetic architecture in the ECB and ACB. However, this conclusion must be considered in light of the constraints inherent to genome scan approaches and of the intricate evolution of adaptation and reproductive isolation in the Ostrinia spp. complex.     

Quantitative characterization of intrinsic disorder in polyglutamine: insights from analysis based on polymer theories

Intrinsically disordered proteins (IDPs) are unfolded under physiological conditions. Here we ask if archetypal IDPs in aqueous milieus are best described as swollen disordered coils in a good solvent or collapsed disordered globules in a poor solvent. To answer this question, we analyzed data from molecular simulations for a 20-residue polyglutamine peptide and concluded, in accord with experimental results, that water is a poor solvent for this system. The relevance of monomeric polyglutamine is twofold: It is an archetypal IDP sequence and its aggregation is associated with nine neurodegenerative diseases. The main advance in this work lies in our ability to make accurate assessments of solvent quality from analysis of simulations for a single, rather than multiple chain lengths. We achieved this through the proper design of simulations and analysis of order parameters that are used to describe conformational equilibria in polymer physics theories. Despite the preference for collapsed structures, we find that polyglutamine is disordered because a heterogeneous ensemble of conformations of equivalent compactness is populated at equilibrium. It is surprising that water is a poor solvent for polar polyglutamine and the question is: why? Our preliminary analysis suggests that intrabackbone interactions provide at least part of the driving force for the collapse of polyglutamine in water. We also show that dynamics for conversion between distinct conformations resemble structural relaxation in disordered, glassy systems, i.e., the energy landscape for monomeric polyglutamine is rugged. We end by discussing generalizations of our methods to quantitative studies of conformational equilibria of other low-complexity IDP sequences.     

Detecting and Measuring Selection from Gene Frequency Data

The recent advent of high-throughput sequencing and genotyping technologies makes it possible to produce, easily and cost effectively, large amounts of detailed data on the genotype composition of populations. Detecting locus-specific effects may help identify those genes that have been, or are currently, targeted by natural selection. How best to identify these selected regions, loci, or single nucleotides remains a challenging issue. Here, we introduce a new model-based method, called SelEstim, to distinguish putative selected polymorphisms from the background of neutral (or nearly neutral) ones and to estimate the intensity of selection at the former. The underlying population genetic model is a diffusion approximation for the distribution of allele frequency in a population subdivided into a number of demes that exchange migrants. We use a Markov chain Monte Carlo algorithm for sampling from the joint posterior distribution of the model parameters, in a hierarchical Bayesian framework. We present evidence from stochastic simulations, which demonstrates the good power of SelEstim to identify loci targeted by selection and to estimate the strength of selection acting on these loci, within each deme. We also reanalyze a subset of SNP data from the Stanford HGDP–CEPH Human Genome Diversity Cell Line Panel to illustrate the performance of SelEstim on real data. In agreement with previous studies, our analyses point to a very strong signal of positive selection upstream of the LCT gene, which encodes for the enzyme lactase–phlorizin hydrolase and is associated with adult-type hypolactasia. The geographical distribution of the strength of positive selection across the Old World matches the interpolated map of lactase persistence phenotype frequencies, with the strongest selection coefficients in Europe and in the Indus Valley.     

The transcription factor Pax6 is required for development of the diencephalic dorsal midline secretory radial glia that form the subcommissural organ.

During brain development, Pax6 is expressed in specific regions of the diencephalon including secretory cells of the subcommissural organ (SCO), a circumventricular organ at the forebrain-midbrain boundary that originates from the pretectal dorsal midline neuroepithelial cells beneath the posterior commissure (PC). Homozygous small eye (Sey/Sey) mice lack functional Pax6 protein and fail to develop the SCO, a normal PC and the pineal gland. Small eye heterozygotes (Sey/+) show defective development of the SCO's basal processes which normally penetrate the PC, indicating that normal development of the gland requires normal Pax6 gene-dosage. A correlation between the defects of SCO formation and altered R- and OB-cadherin expression patterns in the SCO is observed in mutants suggesting a role for cadherins in SCO development.     

New insights into cortical interneurons development and classification: contribution of developmental studies

The concerted development of GABAergic interneurons and glutamatergic neurons is a key feature in the construction of the cerebral cortex. In contrast with glutamatergic neurons, GABAergic interneurons are heterogeneous differing by their axonal and dendritic morphologies, biochemical markers, connectivity, and physiology. Furthermore, interneurons have recently been shown to be generated in a variety of telencephalic structures (the ganglionic eminences, the entopeduncular and preoptic areas and the cortex). This review describes the origin, specification and differentiation of interneurons. These recent developmental studies may help to clarify the classification of mature interneurons. In particular recent studies, including our own, provide compelling evidences that most interneurons are specify after their last division in their region of origin before migration. The roles of target tissues in determining the final physiological properties of interneurons are also discussed.     

Using the TAP component of the antigen-processing machinery as a molecular adjuvant

We hypothesize that over-expression of transporters associated with antigen processing (TAP1 and TAP2), components of the major histocompatibility complex (MHC) class I antigen-processing pathway, enhances antigen-specific cytotoxic activity in response to viral infection. An expression system using recombinant vaccinia virus (VV) was used to over-express human TAP1 and TAP2 (VV-hTAP1,2) in normal mice. Mice coinfected with either vesicular stomatitis virus plus VV-hTAP1,2 or Sendai virus plus VV-hTAP1,2 increased cytotoxic lymphocyte (CTL) activity by at least 4-fold when compared to coinfections with a control vector, VV encoding the plasmid PJS-5. Coinfections with VV-hTAP1,2 increased virus-specific CTL precursors compared to control infections without VV-hTAP1,2. In an animal model of lethal viral challenge after vaccination, VV-hTAP1,2 provided protection against a lethal challenge of VV at doses 100-fold lower than control vector alone. Mechanistically, the total MHC class I antigen surface expression and the cross-presentation mechanism in spleen-derived dendritic cells was augmented by over-expression of TAP. Furthermore, VV-hTAP1,2 increases splenic TAP transport activity and endogenous antigen processing, thus rendering infected targets more susceptible to CTL recognition and subsequent killing. This is the first demonstration that over-expression of a component of the antigen-processing machinery increases endogenous antigen presentation and dendritic cell cross-presentation of exogenous antigens and may provide a novel and general approach for increasing immune responses against pathogens at low doses of vaccine inocula.     

Conserved amino acid markers from past influenza pandemic strains

Background  

Finding the amino acid mutations that affect the severity of influenza infections remains an open and challenging problem. Of special interest is better understanding how current circulating influenza strains could evolve into a new pandemic strain. Influenza proteomes from distinct viral phenotype classes were searched for class specific amino acid mutations conserved in past pandemics, using reverse engineered linear classifiers.     

Presence of Anti-Microbial Antibodies in Liver Cirrhosis – A Tell-Tale Sign of Compromised Immunity?

Background

Bacterial translocation plays important role in the complications of liver cirrhosis. Antibody formation against various microbial antigens is common in Crohn''s disease and considered to be caused by sustained exposure to gut microflora constituents. We hypothesized that anti-microbial antibodies are present in patients with liver cirrhosis and may be associated with the development of bacterial infections.

Methodology/Principal Findings

Sera of 676 patients with various chronic liver diseases (autoimmune diseases:266, viral hepatitis C:124, and liver cirrhosis of different etiology:286) and 100 controls were assayed for antibodies to Saccharomyces cerevisiae(ASCA) and to antigens derived from two intestinal bacterial isolates (one gram positive, one gram negative, neither is Escherichia coli). In patients with liver cirrhosis, we also prospectively recorded the development of severe episodes of bacterial infection. ASCA and anti-OMP Plus™ antibodies were present in 38.5% and 62.6% of patients with cirrhosis and in 16% and 20% of controls, respectively (p<0.001). Occurrence of these antibodies was more frequent in cases of advanced cirrhosis (according to Child-Pugh and MELD score; p<0.001) or in the presence of ascites (p<0.001). During the median follow-up of 425 days, 81 patients (28.3%) presented with severe bacterial infections. Anti-microbial antibody titers (p = 0.003), as well as multiple seroreactivity (p = 0.036), was associated with infectious events. In logistic regression analysis, the presence of ascites (OR:1.62, 95%CI:1.16–2.25), co-morbidities (OR:2.22, 95%CI:1.27–3.86), and ASCA positivity (OR:1.59, 95%CI:1.07–2.36) were independent risk factors for severe infections. A shorter time period until the first infection was associated with the presence of ASCA (p = 0.03) and multiple seropositivity (p = 0.037) by Kaplan-Meier analysis, and with Child-Pugh stage (p = 0.018, OR:1.85) and co-morbidities (p<0.001, OR:2.02) by Cox-regression analysis.

Conclusions/Significance

The present study suggests that systemic reactivity to microbial components reflects compromised mucosal immunity in patients with liver cirrhosis, further supporting the possible role of bacterial translocation in the formation of anti-microbial antibodies.