Nuclear Factor I A and Nuclear Factor I B Are Jointly Required for Mouse Postnatal Neural Stem Cell Self-Renewal

Mouse postnatal neural stem cells (pNSCs) can be expanded in vitro in the presence of epidermal growth factor and fibroblast growth factor 2 and upon removal of these factors cease proliferation and generate neurons, astrocytes, and oligodendrocytes. The genetic requirements for self-renewal and lineage-commitment of pNSCs are incompletely understood. In this study, we show that the transcription factors NFIA and NFIB, previously shown individually, to be essential for the normal commitment of pNSCs to the astrocytic lineage in vivo, are jointly required for normal self-renewal of pNSCs in vitro and in vivo. Using conditional knockout alleles of Nfia and Nfib, we show that the simultaneous loss of these two genes under self-renewal conditions in vitro reduces the expression of the proliferation markers PCNA and Ki67, eliminates clonogenicity of the cells, reduces the number of cells in S phase, and induces aberrant differentiation primarily into the neuroblast lineage. This phenotype requires the loss of both genes and is not seen upon loss of Nfia or Nfib alone, nor with combined loss of Nfia and Nfix or Nfib and Nfix. These data demonstrate a unique combined requirement for both Nfia and Nfib for pNSC self-renewal.

Opposing, spatially-determined epigenetic forces impose restrictions on stochastic olfactory receptor choice

Olfactory receptor (OR) choice represents an example of genetically hardwired stochasticity, where every olfactory neuron expresses one out of ~2000 OR alleles in the mouse genome in a probabilistic, yet stereotypic fashion. Here, we propose that topographic restrictions in OR expression are established in neuronal progenitors by two opposing forces: polygenic transcription and genomic silencing, both of which are influenced by dorsoventral gradients of transcription factors NFIA, B, and X. Polygenic transcription of OR genes may define spatially constrained OR repertoires, among which one OR allele is selected for singular expression later in development. Heterochromatin assembly and genomic compartmentalization of OR alleles also vary across the axes of the olfactory epithelium and may preferentially eliminate ectopically expressed ORs with more dorsal expression destinations from this 'privileged' repertoire. Our experiments identify early transcription as a potential 'epigenetic' contributor to future developmental patterning and reveal how two spatially responsive probabilistic processes may act in concert to establish deterministic, precise, and reproducible territories of stochastic gene expression.

Opposing, spatially-determined epigenetic forces impose restrictions on stochastic olfactory receptor choice

Olfactory receptor (OR) choice represents an example of genetically hardwired stochasticity, where every olfactory neuron expresses one out of ~2000 OR alleles in a probabilistic, yet stereotypic fashion. Here, we propose that topographic restrictions in OR expression are established in neuronal progenitors by two opposing forces: polygenic transcription and genomic silencing, both of which are influenced by dorsoventral gradients of transcription factors NFIA, B, and X. Polygenic transcription of OR genes may define spatially constrained OR repertoires, among which one OR allele is selected for singular expression later in development. Heterochromatin assembly and genomic compartmentalization of OR alleles also vary across the axes of the olfactory epithelium and may preferentially eliminate ectopically expressed ORs with more dorsal expression destinations from this "privileged" repertoire. Our experiments identify early transcription as a potential "epigenetic" contributor to future developmental patterning and reveal how two spatially responsive probabilistic processes may act in concert to establish deterministic, precise, and reproducible territories of stochastic gene expression.

Simulation of TTT Curves for Additively Manufactured Inconel 625

The ability to use common computational thermodynamic and kinetic tools to study the microstructure evolution in Inconel 625 (IN625) manufactured using the additive manufacturing (AM) technique of laser powder-bed fusion is evaluated. Solidification simulations indicate that laser melting and re-melting during printing produce highly segregated interdendritic regions. Precipitation simulations for different degrees of segregation show that the larger the segregation, i.e., the richer the interdendritic regions are in Nb and Mo, the faster the δ-phase (Ni₃Nb) precipitation. This is in accordance with the accelerated d precipitation observed experimentally during post-build heat treatments of AM IN625 compared to wrought IN625. The δ-phase may be undesirable since it can lead to detrimental effects on the mechanical properties. The results are presented in the form of a TTT diagram and agreement between the simulated diagram and the experimental TTT diagram demonstrate how these computational tools can be used to guide and optimize post-build treatments of AM materials.

The Influence of Annealing Temperature and Time on the Formation of δ-Phase in Additively-Manufactured Inconel 625

This research evaluated the kinetics of δ-phase growth in laser powder bed additively-manufactured (AM) Inconel 625 during post-build stress-relief heat treatments. The temperatures ranged between 650°C and 1050°C, and the times from 0.25 to 168 hours. The presence of δ-phase was verified for each temperature/time combination through multiple techniques. A conventional time-temperature-transformation diagram was constructed from the time-temperature data. Comparison to the growth in wrought IN625 with a similar nominal composition revealed that δ-phase formation occurred at least two orders of magnitude faster in the AM IN625. The results of this study also revealed that the segregated microstructure in the as-built condition has a strong influence on the kinetics of δ-phase formation in AM IN625 as compared to a homogenized material. Since control of the δ-phase growth is essential for reliable prediction of the performance of IN625 components in service, avoiding heat treatments that promote the formation of δ-phase in AM components that are not homogenized is highly recommended. This will be particularly true at elevated temperatures where the microstructural stability and the consistency of mechanical properties are more likely to be affected by the presence of δ-phase.

The blemishes of modern society? Acne prevalence in the Dogon of Mali

BACKGROUND AND OBJECTIVES

Non-communicable diseases may reflect an evolutionary mismatch between our human ancestry and modern environments. To explore the mismatch hypothesis for Acne vulgaris, we studied the prevalence and severity of acne in Dogon adolescents in Mali, West Africa.

METHODOLOGY

We graded the prevalence and severity of acne in 1182 Dogon adolescents aged 11-18 years from nine villages using facial photos taken as part of a prospective cohort study. Eighty-nine (89%) of the individuals in the cohort migrated to the city during adolescence, enabling us to assess the effect of urban migration. Using multivariable logistic regression, we estimated the effect of predictor variables on the presence of acne.

RESULTS

The prevalence of acne in the cohort was 28%, with 90% of cases being mild or very mild. Thus, the prevalence and severity of acne was much lower than for adolescents in high-income countries. Controlling for age, puberty, and body mass index (BMI), the odds of boys developing acne was 85% lower in the city than in the villages (P = 0.002).

CONCLUSION AND IMPLICATIONS

Acne is similar to the 'diseases of civilization' in being promoted by the pro-inflammatory properties of modern diets. The low prevalence and severity of acne in the Dogon supports the mismatch hypothesis and suggests that acne should join the list of diseases of modern lifestyles. However, we also observed an unexpected decrease in acne in urban boys. Future research is needed for a deeper mechanistic understanding of the interplay between diet, inflammation, immune function and other environmental exposures that differ between urban and rural environments.

Valence-bond crystalline order in the s = 1/2 J1-J2 model on the honeycomb lattice

Using the coupled cluster method we study the phase diagram of the spin-1/2 Heisenberg antiferromagnet on a honeycomb lattice with nearest-neighbour exchange coupling J1 > 0 and frustrating next-nearest-neighbour coupling J2 ≡ xJ1 > 0. In the range 0 < x < 1 we find four phases exhibiting respectively Néel, 6-spin plaquette, staggered dimer and Néel-II orderings, with quantum critical points at xc1 ≈ 0.207(3), xc2 ≈ 0.385(10) and xc3 ≈ 0.65(5). The transitions at xc1 and xc3 appear to be continuous (and hence deconfined) ones, while that at xc2 appears to be a direct first-order one.

The frustrated Heisenberg antiferromagnet on the honeycomb lattice: J1-J2 model

We study the ground-state phase diagram of the frustrated spin-[Formula: see text] antiferromagnet with J(2) = xJ(1) > 0 (J(1) > 0) on the honeycomb lattice, using the coupled-cluster method. We present results for the ground-state energy, magnetic order parameter and plaquette valence-bond crystal (PVBC) susceptibility. We find a paramagnetic PVBC phase for x(c(1)) < x < x(c(2)), where x(c(1)) ≈ 0.207 ± 0.003 and x(c(2)) ≈ 0.385 ± 0.010. The transition at x(c(1)) to the Néel phase seems to be a continuous deconfined transition (although we cannot exclude a very narrow intermediate phase in the range 0.21 ≲ x ≲ 0.24), while that at x(c(2)) is of first-order type to another quasiclassical antiferromagnetic phase that occurs in the classical version of the model only at the isolated and highly degenerate critical point [Formula: see text]. The spiral phases that are present classically for all values x > 1/6 are absent for all x ≲ 1.

Mesenchymal nuclear factor I B regulates cell proliferation and epithelial differentiation during lung maturation

The Nuclear factor I (NFI) transcription factor family consists of four genes (Nfia, Nfib, Nfic and Nfix) that regulate the development of multiple organ systems in mice and humans. Nfib is expressed in both lung mesenchyme and epithelium and mice lacking Nfib have severe lung maturation defects and die at birth. Here we continue our analysis of the phenotype of Nfib⁻/⁻ lungs and show that Nfib specifically in lung mesenchyme controls late epithelial and mesenchymal cell proliferation and differentiation. There are more PCNA, BrdU, PHH3 and Ki67 positive cells in Nfib⁻/⁻ lungs than in wild type lungs at E18.5 and this increase in proliferation marker expression is seen in both epithelial and mesenchymal cells. The loss of Nfib in all lung cells decreases the expression of markers for alveolar epithelial cells (Aqp5 and Sftpc), Clara cells (Scgb1a1) and ciliated cells (Foxj1) in E18.5 lungs. To test for a specific role of Nfib in lung mesenchyme we generated and analyzed Nfib(flox/flox), Dermo1-Cre mice. Loss of Nfib only in mesenchyme results in decreased Aqp5, Sftpc and Foxj1 expression, increased cell proliferation, and a defect in sacculation similar to that seen in Nfib⁻/⁻ mice. In contrast, mesenchyme specific loss of Nfib had no effect on the expression of Scgb1a1 in the airway. Microarray and QPCR analyses indicate that the loss of Nfib in lung mesenchyme affects the expression of genes associated with extracellular matrix, cell adhesion and FGF signaling which could affect distal lung maturation. Our data indicate that mesenchymal Nfib regulates both mesenchymal and epithelial cell proliferation through multiple pathways and that mesenchymal NFI-B-mediated signals are essential for the maturation of distal lung epithelium.

Nfix regulates fetal-specific transcription in developing skeletal muscle

Skeletal myogenesis, like hematopoiesis, occurs in successive developmental stages that involve different cell populations and expression of different genes. We show here that the transcription factor nuclear factor one X (Nfix), whose expression is activated by Pax7 in fetal muscle, in turn activates the transcription of fetal specific genes such as MCK and beta-enolase while repressing embryonic genes such as slow myosin. In the case of the MCK promoter, Nfix forms a complex with PKC theta that binds, phosphorylates, and activates MEF2A. Premature expression of Nfix activates fetal and suppresses embryonic genes in embryonic muscle, whereas muscle-specific ablation of Nfix prevents fetal and maintains embryonic gene expression in the fetus. Therefore, Nfix acts as a transcriptional switch from embryonic to fetal myogenesis.

The transcription factor Nfix is essential for normal brain development

Background

The Nuclear Factor I (NFI) multi-gene family encodes site-specific transcription factors essential for the development of a number of organ systems. We showed previously that Nfia-deficient mice exhibit agenesis of the corpus callosum and other forebrain defects; Nfib-deficient mice have defects in lung maturation and show callosal agenesis and forebrain defects resembling those seen in Nfia-deficient animals, while Nfic-deficient mice have defects in tooth root formation. Recently the Nfix gene has been disrupted and these studies indicated that there were largely uncharacterized defects in brain and skeletal development in Nfix-deficient mice.

Results

Here we show that disruption of Nfix by Cre-recombinase mediated excision of the 2nd exon results in defects in brain development that differ from those seen in Nfia and Nfib KO mice. In particular, complete callosal agenesis is not seen in Nfix-/- mice but rather there appears to be an overabundance of aberrant Pax6- and doublecortin-positive cells in the lateral ventricles of Nfix-/- mice, increased brain weight, expansion of the cingulate cortex and entire brain along the dorsal ventral axis, and aberrant formation of the hippocampus. On standard lab chow Nfix-/- animals show a decreased growth rate from ~P8 to P14, lose weight from ~P14 to P22 and die at ~P22. If their food is supplemented with a soft dough chow from P10, Nfix-/- animals show a lag in weight gain from P8 to P20 but then increase their growth rate. A fraction of the animals survive to adulthood and are fertile. The weight loss correlates with delayed eye and ear canal opening and suggests a delay in the development of several epithelial structures in Nfix-/- animals.

Conclusion

These data show that Nfix is essential for normal brain development and may be required for neural stem cell homeostasis. The delays seen in eye and ear opening and the brain morphology defects appear independent of the nutritional deprivation, as rescue of perinatal lethality with soft dough does not eliminate these defects.

Functional role of conserved transmembrane segment 1 residues in human sodium-dependent vitamin C transporters

Sodium-dependent vitamin C transporters, SVCT1 and SVCT2, are the only two known proteins for the uptake of ascorbate, the active form of vitamin C. Little structural information is available for SVCTs, although a transport activity increase from pH 5.5 to 7.5 suggests a functional role of one or more conserved histidines (p K a approximately 6.5). Confocal fluorescence microscopy and uptake kinetic analyses were used here to characterize cells transfected with mutants of EGFP-tagged hSVCTs. Mutating any of the four conserved histidine residues (His51, 147, 210, or 354) in hSVCT1 to alanine did not affect the apical membrane localization in polarized MDCK cells. His51Ala (in putative transmembrane segment 1, TM1) was the only mutation that resulted in a significant loss of ascorbate transport and an increase in apparent Km with no significant effect on Vmax. The corresponding mutation in hSVCT2, His109Ala, also led to a loss of transport activity. Among eight other mutations of His51 in hSVCT1, significant sodium-dependent ascorbate transport activity was only observed with asparagine or tyrosine replacement. Thus, our results suggest that uncharged His51, directly or indirectly, contributes to substrate binding through the hydrogen bond. His51 cannot account for the observed pH dependence as neutral amino acid substitutions failed to abolish the pH-dependent activity increase. The importance of TM1 is further strengthened by the comparable loss of sodium-dependent ascorbate transport activity upon the mutation of adjacent conserved Gln50 and the apparent change in substrate specificity in the hSVCT1-His51Gln mutation, which showed a specific increase in sodium-independent dehydroascorbate transport.

Human TBX1 missense mutations cause gain of function resulting in the same phenotype as 22q11.2 deletions

Deletion 22q11.2 syndrome is the most frequent known microdeletion syndrome and is associated with a highly variable phenotype, including DiGeorge and Shprintzen (velocardiofacial) syndromes. Although haploinsufficiency of the T-box transcription factor gene TBX1 is thought to cause the phenotype, to date, only four different point mutations in TBX1 have been reported in association with six of the major features of 22q11.2 deletion syndrome. Although, for the two truncating mutations, loss of function was previously shown, the pathomechanism of the missense mutations remains unknown. We report a novel heterozygous missense mutation, H194Q, in a familial case of Shprintzen syndrome and show that this and the two previously reported missense mutations result in gain of function, possibly through stabilization of the protein dimer DNA complex. We therefore conclude that TBX1 gain-of-function mutations can result in the same phenotypic spectrum as haploinsufficiency caused by loss-of-function mutations or deletions.

T-box proteins differentially activate the expression of the endogenous interferon γ gene versus transfected reporter genes in non-immune cells

The T-box transcription factor T-bet is expressed in a number of hematopoetic cell types and plays an essential role in the lineage determination of Th1 T-helper cells. In the absence of T-bet, CD4(+) T-cells fail to induce IFNgamma, the cytokine whose expression characterizes Th1 cells. Here we show that, surprisingly, T-bet induces the expression of endogenous IFNgamma in non-immune human cells, including 293 and other cell lines. Thus T-bet can induce IFNgamma expression independently of its role in T-cell lineage determination. In addition, mutations in T-bet, and chimeras of T-bet with other transcription factors including the T-box transcription factor, TBX2, differentially affect the ability of T-bet to activate expression of endogenous IFNgamma versus a T-site regulated reporter gene. A truncated T-betVp16 fusion protein strongly activates the T-site reporter but fails to activate endogenous IFNgamma. Conversely, native T-bet strongly activates endogenous IFNgamma expression but only weakly activates the reporter gene. Fusion of the Vp16 activation domain to full-length T-bet greatly increases its activation of both endogenous IFNgamma and transfected T-site reporter gene expression. In contrast, TBX2Vp16 potently activates the T-site reporter but has a negligible effect on endogenous IFNgamma expression. Butyrate treatment of T-bet expressing cells potentiates the expression of endogenous IFNgamma but weakly represses expression of the T-site reporter gene. These data indicate that induction of endogenous IFNgamma can be uncoupled from differentiation into the Th1 lineage and that the expression of endogenous IFNgamma versus a T-site reporter gene is differentially regulated by T-bet and other T-box proteins.

Polarized localization of vitamin C transporters, SVCT1 and SVCT2, in epithelial cells

Messenger RNA of homologous sodium-vitamin C cotransporters, SVCT1 and SVCT2, were found in the intestine. Studies using cultured intestinal cells suggested an apical presence of SVCT1 but the function of SVCT2 was unknown. Here, we showed that enterocytes from heterozygous SVCT2-knockout mice had lower sodium-dependent vitamin C accumulation compared to those from the wildtype. Thus, SVCT2 appears to be functional in enterocytes. We then tested whether SVCT2 could have a redundant function as SVCT1 by constructing and expressing EGFP-tagged SVCTs in intestinal Caco-2 and kidney MDCK cells. In confluent epithelial cells, SVCT1 protein expressed predominantly on the apical membrane. SVCT2, in contrast, accumulated at the basolateral surface. Functionally, SVCT1 expression led to more transport activity from the apical membrane, while SVCT2 expression only increased the uptake under the condition when basolateral membrane was exposed. This differential epithelial membrane distribution and function suggests non-redundant functions of these two isoforms.

Differential target gene activation by TBX2 and TBX2VP16: evidence for activation domain-dependent modulation of gene target specificity

The determinants of in vivo target site selectivity by transcription factors are poorly understood. To find targets for the developmentally regulated transcription factor TBX2, we generated stable transfectants of human embryonic kidney cells (293) that express a TBX2-ecdysone receptor (EcR) chimeric protein. While constitutive expression of TBX2 is toxic to 293 cells, clones expressing TBX2EcR are viable in the absence of an EcR ligand. Using cDNA arrays and quantitative PCR, we discovered nine genes whose expression was increased, but no genes whose expression was reduced, following 24 h of induction with Ponasterone A (PonA), a ligand for EcR. Since TBX2 was reported previously to be a transcriptional repressor, we also generated cell lines expressing a TBX2VP16EcR protein which we showed was a potent conditional transcriptional activator in transient transfection assays. Treatment of these cells with PonA induced the expression of five genes, none of which were affected in TBX2EcR-expressing cells. This discordance between TBX2- and TBX2VP16-regulated genes strongly suggests that specific transactivation domains can be a major determinant of gene target site selectivity by transcription factors that possess the same DNA-binding domain.

Rainfall events and downstream drift of microcrustacean zooplankton in a Newfoundland boreal stream

While rainfall events may lead to flushing of zooplankton from lakes, with implications for stream productivity near lake outlets, consideration also needs to be given to zooplankton transported farther downstream. To evaluate such downstream transport, daytime invertebrate drift, stream discharge, and rainfall events were monitored over 4 summers in Cook's Brook, Newfoundland, at a downstream site 1.0 km below the outlet of Big Cook's Pond and an upstream site 1.0 km upstream of the pond. Microcrustacean zooplankton were abundant in some downstream samples; high percent zooplankton abundance (87–94%) corresponded to the highest total invertebrate drift densities. Percent zooplankton in downstream drift was strongly correlated with recent rainfall (rS = 0.815, p = 0.025) and stream discharge (rS = 0.964, p = 0.001). The majority of microcrustaceans in the drift were planktonic cladocerans and copepods, the species composition being similar to that in Big Cook's Pond. No zooplankton were ever collected from the upstream site. Ephemeroptera, Diptera, Trichoptera, and Ostracoda were abundant in most drift samples. Zooplankton drift (mean = 0.17 individuals/m3) in Cook's Brook appears to be catastrophic drift, with high precipitation rates and resultant increased flushing rate in Big Cook's Pond leading to "washout" of microcrustaceans 1 km downstream.

A virus-like agent associated with neurofibromatosis in damselfish

Damselfish neurofibromatosis (DNF) is a transmissible disease involving neurofibromas and chromatophoromas affecting bicolor damselfish Stegastes partitus on Florida reefs. Analysis of genomic DNA by Southern blotting techniques demonstrated the presence of a group of extrachromosomal DNAs in tumors from fish affected with DNF but not in healthy individuals. Cell lines obtained from tumors contained identical DNAs and were shown to be tumorigenic in vivo, while lines established from healthy fish did not contain such DNA and were not tumorigenic. These DNA patterns were also observed in experimentally induced tumors. A DNase resistant component of this DNA was isolated from both tumor cells and conditioned media of tumor cell lines suggesting that these sequences were encapsulated in viral particles. These data support the hypothesis that one or more of these extrachromosomal DNA forms is the genome of an unusual virus and that this virus is the etiologic agent of DNF. We have tentatively termed this agent the damselfish virus-like agent (DVLA).

A dominant repression domain in Tbx3 mediates transcriptional repression and cell immortalization: relevance to mutations in Tbx3 that cause ulnar-mammary syndrome

Mutations in Tbx3 are responsible for ulnar-mammary syndrome (UMS), an autosomal dominant disorder affecting limb, tooth, hair, apocrine gland and genital development. Tbx3 is a member of a family of transcription factors that share a highly conserved DNA-binding domain known as the T-domain. UMS-causing mutations in Tbx3 have been found at numerous sites within the TBX3 gene, with many occurring downstream from the N-terminally located T-domain. The occurrence of mutations downstream of the DNA-binding domain raises the possibility that there exist important functional domains in C-terminal portions of the Tbx3 protein that affect its behavior as a transcription factor. To determine if and how such C-terminal mutations affect transcription we have mapped regions that confer transcriptional activity and nuclear localization and characterized the DNA binding properties of Tbx3. We find that Tbx3 binds the canonical Brachyury binding site as a monomer and represses transcription. We show that a key repression domain (RD1) resides in the Tbx3 C-terminus that can function as a portable repression domain. Most UMS-associated C-terminal mutants lack the RD1 and exhibit decreased or loss of transcriptional repression activity. In addition, we identify a domain responsible for nuclear localization of Tbx3 and show that two C-terminal mutants of Tbx3 have increased rates of protein decay. Finally, we show that Tbx3 can immortalize primary embryo fibroblasts and that the RD1 repression domain is required for this activity. Our results identify critical functional domains within the Tbx3 protein and facilitate interpretation of the functional consequences of present and future UMS mutations.

Progression of infection and tumor development in damselfish

The bicolor damselfish (Stegastes partitus) is a tropical marine teleost naturally affected by multiple neurofibromas and chromatophoromas on South Florida reefs. Damselfish neurofibromatosis is a transmissible disease caused by a subcellular agent. Development of tumors is associated with the appearance of a series of extrachromosomal DNAs ranging in size from 1.2 to 7 kb that appear to be the genome of a small virus-like agent which we termed the damselfish virus-like agent (DVLA). This DNA was found at high copy number in most spontaneous and experimentally induced tumors. An essentially identical pattern of DNA, but with lower copy numbers, was observed in non-tumor-bearing tissue from diseased fish. Copy numbers of DVLA DNA in tumors and nontumorous tissues increased as the disease progressed from early to late stages. In healthy fish in which DVLA DNA was detected, the quantities were much lower than those in diseased fish. Healthy fish from populations with a high prevalence of disease exhibited more infected tissues than fish from populations with low levels.

A biomechanical evaluation of the Christensen temporomandibular joint implant

The Christensen TMJ implant is often used clinically as a total joint replacement of the temporomandibular joint. The system consists of a thin fossa component and a condylar component with a polished articular head. In this study, we analyzed the surface finish and the metal structure of the components. We also measured the contact areas between the two components for different load levels. Such information may be useful in evaluating clinical performance as well as in making future improvements in the design of these implants.

Differential DNA binding and transcription modulation by three T-box proteins, T, TBX1 and TBX2

T-box genes encode a family of phylogenetically conserved DNA-binding proteins that regulate gene expression during embryogenesis. While the developmental importance of many T-box genes has been well documented, little is known about how family members differ in their DNA binding properties and ability to modulate transcription. Here we show that although TBX1, TBX2 and the Xenopus T protein (Xbra) share only 50-60% identity within their DNA-binding domains they can bind the same DNA sequence in vitro. However, the proteins differ in three important respects. While TBX1 protein binds a palindromic T oligonucleotide as a dimer, as had been previously reported for Xbra, TBX2 appears to bind the same DNA sequence as a monomer. Also, T protein/DNA complexes are stabilized in vitro by the addition of specific antibodies, whereas TBX2/DNA complexes are not stabilized by antibodies. Most importantly, TBX2 represses while Xbra activates transcription of the same chimeric reporter plasmid. TBX1, although capable of binding to the chimeric promoter, has no effect on transcription. Thus, while the DNA binding domains of T-box proteins share substantial homology, these proteins differ in both their DNA binding and transcriptional modulation properties. These results suggest that the various T-box proteins, while highly conserved, likely use different mechanisms to modulate transcription and may have different targets in vivo.

Different brain networks mediate task performance in normal aging and AD: defining compensation

OBJECTIVE

To determine whether the pathologic mechanisms of AD alter the brain networks subserving performance of a verbal recognition task.

BACKGROUND

Functional imaging studies comparing task-related activation in AD patients and controls generally have not used network analysis and have not controlled for task difficulty.

METHODS

H2 15O PET was used to measure regional cerebral blood flow in 14 patients and 11 healthy elders during the performance of a serial verbal recognition task under two conditions: low demand, with study list size (SLS) equal to one; and titrated demand, with SLS adjusted so that each subject recognized words at 75% accuracy. The Scaled Subprofile Model was used to identify networks of regionally covarying activity across these task conditions.

RESULTS

In the elders, higher SLS was associated with the recruitment of a network of brain areas involving left anterior cingulate and anterior insula (R2 = 0.94; p < 0.0001). Three patients also expressed this network. In the remaining patients, higher SLS was associated with the recruitment of an alternate network consisting of left posterior temporal cortex, calcarine cortex, posterior cingulate, and the vermis (R2 = 0.81, p < 0.001). Expression of this network was unrelated to SLS in the elders and more intact AD patients.

CONCLUSIONS

The patients' use of the alternate network may indicate compensation for processing deficits. The transition from the normal to the alternate network may indicate a point where brain disease has irreversibly altered brain function and thus may have important implications for therapeutic intervention.

Molecular characterization of a urea transporter in the gill of the gulf toadfish (Opsanus beta)

Urea excretion by the gulf toadfish (Opsanus beta) has been shown in previous studies to be a highly pulsatile facilitated transport, with excretion probably occurring at the gill. The present study reports the isolation of an 1800 base pair (kb) cDNA from toadfish gill with one open reading frame putatively encoding a 475-residue protein, the toadfish urea transporter (tUT). tUT, the first teleostean urea transporter cloned, has high homology with UTs (facilitated urea transporters) cloned from mammals, an amphibian and a shark, and most closely resembles the UT-A subfamily. When expressed in Xenopus laevis oocytes, tUT increased urea permeability (as measured by [(14)C]urea uptake) five- to sevenfold, and this permeability increase was abolished by phloretin, a common inhibitor of other UTs. Northern analysis using the 1.8 kb clone was performed to determine the tissue distribution and dynamics of tUT mRNA expression. Of six tissues examined (gill, liver, red blood cells, kidney, skin and intestine), only gill showed expression of tUT mRNA, with a predominant band at 1.8 kb and a minor band at 3.5 kb. During several points in the urea pulse cycle of toadfish (0, 4, 6, 12 and 18 h post-pulse), measured by excretion of [(14)C]urea into the water, gill mRNA samples were obtained. Expression of tUT mRNA was found to be largely invariant relative to expression of beta-actin mRNA over the pulse cycle. These results further confirm the gill localization of urea transport in the toadfish and suggest that tUT regulation (and the regulation of pulsatile urea excretion) is probably not at the level of mRNA control. The results are discussed in the context of the mechanisms of vasopressin-regulated UT-A in mammalian kidney and morphological data for the toadfish gill.

Reproducibility of alternative probe synthesis approaches for gene expression profiling with arrays

Before gene expression profiling with microarray technology can be transferred to the diagnostic setting, we must have alternative approaches for synthesizing probe from limited RNA samples, and we must understand the limits of reproducibility in interpreting gene expression results. The current gold standard of probes for use with both microarrays and high-density filter arrays are synthesized from 1 microg of purified poly(A)+ RNA. We evaluated two approaches for synthesizing cDNA probes from total RNA with subsequent hybridization to high-density filter arrays: 1) reverse transcription (RT) of 5 microg total RNA and 2) RT-polymerase chain reaction (RT-PCR) of 1 microg total RNA, using the SMART system. The reproducibility of these two approaches was compared to the current gold standard. All three methods were highly reproducible. Triplicate experiments resulted in the following concordance correlation coefficients to evaluate reproducibility: 0.88 for the gold standard, 0.86 for cDNA probe synthesized by RT from total RNA, and 0.96 for the SMART cDNA probe synthesized from total RNA. We also compared the expression profile of 588 genes for the total RNA methods to that obtained with the gold standard. Of 150 positive genes detected by the gold standard, 97 (65%) were detected by cDNA probe synthesized by RT of total RNA, and 122 (81%) were detected by the SMART cDNA probe. We conclude that SMART cDNA probe produces highly reproducible results and yields gene expression profiles that represent the majority of transcripts detected with the gold standard.

Disruption of the murine nuclear factor I-A gene (Nfia) results in perinatal lethality, hydrocephalus, and agenesis of the corpus callosum

The phylogenetically conserved nuclear factor I (NFI) family of transcription/replication proteins is essential both for adenoviral DNA replication and for the transcription of many cellular genes. We showed previously that the four murine NFI genes (Nfia, Nfib, Nfic, and Nfix) are expressed in unique but overlapping patterns during mouse development and in adult tissues. Here we show that disruption of the Nfia gene causes perinatal lethality, with >95% of homozygous Nfia(-/-) animals dying within 2 weeks after birth. Newborn Nfia(-/-) animals lack a corpus callosum and show ventricular dilation indicating early hydrocephalus. Rare surviving homozygous Nfia(-/-) mice lack a corpus callosum, show severe communicating hydrocephalus, a full-axial tremor indicative of neurological defects, male-sterility, low female fertility, but near normal life spans. These findings indicate that while the Nfia gene appears nonessential for cell viability and DNA replication in embryonic stem cells and fibroblasts, loss of Nfia function causes severe developmental defects. This finding of an NFI gene required for a developmental process suggests that the four NFI genes may have distinct roles in vertebrate development.

Transcription repression by Xenopus ET and its human ortholog TBX3, a gene involved in ulnar-mammary syndrome

T box (Tbx) genes are a family of developmental regulators with more than 20 members recently identified in invertebrates and vertebrates. Mutations in Tbx genes have been found to cause several human diseases. Our understanding of functional mechanisms of Tbx products has come mainly from the prototypical T/Brachyury, which is a transcription activator. We previously discovered ET, a Tbx gene expressed in Xenopus embryos. We report here that ET is an ortholog of the human Tbx3 and that ET is a repressor of basal and activated transcription. Functional dissection of the ET protein reveals a novel transcription-repression domain highly conserved among ET, human TBX3, and TBX2. These results reveal a new transcription repressor domain, show the existence of a subfamily of transcription repressors in the Tbx superfamily, and provide a basis for understanding etiology of diseases caused by Tbx3 mutations.

The spectrum of mutations in TBX3: Genotype/Phenotype relationship in ulnar-mammary syndrome

Ulnar-mammary syndrome (UMS) is a pleiotropic disorder affecting limb, apocrine-gland, tooth, hair, and genital development. Mutations that disrupt the DNA-binding domain of the T-box gene, TBX3, have been demonstrated to cause UMS. However, the 3' terminus of the open reading frame (ORF) of TBX3 was not identified, and mutations were detected in only two families with UMS. Furthermore, no substantial homology outside the T-box was found among TBX3 and its orthologues. The subsequent cloning of new TBX3 cDNAs allowed us to complete the characterization of TBX3 and to identify alternatively transcribed TBX3 transcripts, including one that interrupts the T-box. The complete ORF of TBX3 is predicted to encode a 723-residue protein, of which 255 amino acids are encoded by newly identified exons. Comparison of other T-box genes to TBX3 indicates regions of substantial homology outside the DNA-binding domain. Novel mutations have been found in all of eight newly reported families with UMS, including five mutations downstream of the region encoding the T-box. This suggests that a domain(s) outside the T-box is highly conserved and important for the function of TBX3. We found no obvious phenotypic differences between those who have missense mutations and those who have deletions or frameshifts.

Constitutive expression of the Wilms tumor suppressor gene (WT1) in renal cell carcinoma

The expression of the Wilms tumor suppressor gene WT1 is largely restricted to elements of the developing urogenital system. In the fetal kidney, WT1 transcripts are present at low levels in the condensing mesenchyme and at much higher levels in differentiating glomerular epithelium and are not detected in other mesenchymal-derived epithelial structures such as the proximal and distal tubules. However, WT1 expression is observed in tubule-like elements found in some Wilms tumors. As renal cell carcinoma (RCC) of the clear cell type is one of the most prevalent adult tumors of the kidney, and is thought to originate from the epithelial cells of the proximal tubules, we studied WT1 expression in RCCs. Despite the absence of WT1 in normal primary epithelial cells derived from proximal tubules, RCC tumors and tumor-derived cell lines expressed WT1 RNA. Immunocytochemical analyses of tumor cryosections showed widespread expression throughout the poorly differentiated epithelial components of the tumor. Immunoblots of RCC samples detected a normal size WT I protein and reciprocal antibody immunoprecipitations of RCC cell extracts indicated that WT I interacts with p53 as has been demonstrated for normal human fetal kidney. The aberrant expression of functional WT1 in RCC may represent a reversion to a more de-differentiated phenotype and may contribute to the tumorigenic phenotype by inappropriately activating or repressing genes involved in growth regulation.

Genomic structure of TBX2 indicates conservation with distantly related T-box genes

TBX2 is a member of a recently discovered gene family of transcription factors, named T-box genes after the Brachyury or T gene. Mutations in two of these family members, TBX5 and TBX3, have recently been shown to be responsible for the congenital abnormalities associated with Holt Oram syndrome and ulnar-mammary syndrome respectively, while mutations in T-box genes in other species also result in developmental abnormalities in the tissues where the gene is normally expressed. Thus, it likely that other T-box genes are responsible for additional human developmental anomalies. Here we report the exon/intron boundaries of TBX2 and a polymorphism within intron 2 of TBX2 that should be useful for exploring the involvement of this gene in human genetic disease. We further note that the exon/intron boundaries of TBX2 are highly conserved within the T-box domain with those of both T and TBX5, as well as with a new human T-box gene and more distantly related genes from Caenorhabditis elegans and Drosophila. This observation should facilitate the analysis of the genomic structure of other members of this gene family. It is also of interest that several members of this gene family have an additional intron that is variably present within members of at least two different lineages of the T-box family. This observation has implications regarding the evolution of T-box genes.

Tissue-specific regulation of the WT1 locus

The 11p13 Wilms' tumor locus consists of two coordinately regulated transcripts, WT1 and WIT-1. These genes are highly expressed in the developing urogenital system, beginning with the urogenital ridge at day 10.5, the metanephric blastema at day 11.5, and during glomerular formation at day 13.5, becoming ultimately restricted to the podocytes. Stromal cells of the gonad also show abundant expression. WT1 is expressed at lower levels in spleen, uterus, mesothelial linings of organs in the abdominal and thoracic cavities, and the ependymal layer of the ventral aspect of the spinal cord. WIT-1 mRNA is about 10-fold less abundant than WT1, but appears to be expressed in the same tissue-restricted manner. Expression of the WT1 protein is required for kidney development, although its physiological function remains to be determined. The function of WIT-1 is similarly unknown but one intriguing possibility is that it is an antisense regulator of WT1. An understanding of events controlling spatial and temporal regulation of these genes will greatly improve our ability to study the role of WT1 and WIT-1 in urogenital development. We have found that while chimeric reporter constructs containing 0.6-2.5 kb of the 5' region of the WT1 gene direct transcription in many different cell lines, we were unable to detect expression in 13.5-day mouse embryos. However, a cosmid containing about 42 kb encompassing this region was able to direct the expression of abundant levels of mRNA from the appropriate transcription initiation sites in both stable transfectants of mouse Leydig cells (TM3) or in transgenic embryos. We are currently localizing the DNA elements required for this expression.

Regulation of WT1 by phosphorylation: inhibition of DNA binding, alteration of transcriptional activity and cellular translocation

Phosphorylation is one of the major post-translational mechanisms by which the activity of transcription factors is regulated. We have investigated the role of phosphorylation in the regulation of nucleic acid binding activity and the nuclear translocation of WT1. Two recombinant WT1 proteins containing the DNA binding domain with or without a three amino acid (KTS) insertion (WT1ZF + KTS and WT1ZF - KTS) were strongly phosphorylated by protein kinase A (PKA) and protein kinase C (PKC) in vitro. Both PKA and PKC phosphorylation inhibited the ability of WT1ZF + KTS or WT1ZF - KTS to bind to a sequence derived from the WT1 promoter region in gel mobility shift assays. The binding of WT1ZF - KTS to an EGR1 consensus binding site was also inhibited by prior PKA and PKC phosphorylation. We also demonstrate the RNA binding activity of WT1, but this was not altered by phosphorylation. PKA activation by dibutyryl cAMP in WT1-transfected cells resulted in the reversal of WT1 suppression of a reporter construct. Although WT1 protein is predominantly localized to the nucleus, this expression pattern is altered upon PKA activation, resulting in the cytoplasmic retention of WT1. Accordingly, phosphorylation may play a role in modulating the transcriptional regulatory activity of WT1 through interference with nuclear translocation, as well as by inhibition of WT1 DNA binding.

Is there implicit memory after propofol sedation?

Recent evidence indicates that implicit memory may be preserved during general anaesthesia. We tested for the presence of explicit and implicit memory in patients undergoing surgical procedures with local or regional anaesthesia and sedation with propofol. Initial i.v. boluses of propofol 0.5 mg kg-1 and fentanyl 1 microgram kg-1 were administered, followed by an infusion of propofol 50 micrograms kg-1 min-1. Administration of one or more doses of propofol 30 mg i.v. during operation was controlled either by the patient or the anaesthetist. At the start of the last skin stitch, patients were presented with a list of 15 stimulus words and the most frequently associated response. The infusion was then discontinued. After 1 h in the recovery area, all patients were tested for free recall, free association, cued recall and recognition on the list presented during surgery (critical list) and a matched list not presented (neutral list). Data of all patients without free recall (explicit memory) were analysed with repeated-measures analysis of variance. Of 36 patients, five demonstrated free recall. For the remaining 31 patients, cued recall and recognition showed no evidence of explicit memory. However, the free association tests demonstrated significant priming. The mean number of critical free associations was 6.6 (SEM 0.4) compared with 5.5 (0.4) neutral free association (P < 0.05). In the absence of explicit memory, implicit memory persists after intraoperative sedation with propofol.

Synergistic transcriptional activation of the tissue inhibitor of metalloproteinases-1 promoter via functional interaction of AP-1 and Ets-1 transcription factors

The tissue inhibitor of metalloproteinases-1 (TIMP-1) is an inhibitor of the extracellular matrix-degrading metalloproteinases. We characterized response elements that control TIMP-1 gene expression. One contains a binding site that selectively binds c-Fos and c-Jun in vitro and confers a response to multiple AP-1 family members in vivo. Adjacent to this is a binding site for Ets domain proteins. Although c-Ets-1 alone did not activate transcription from this element, it enhanced transcription synergistically with AP-1 either in the context of the natural promoter or when the sequence was linked upstream of a heterologous promoter. Furthermore, a complex of c-Jun and c-Fos interacted with c-Ets-1 in vitro. These results suggest that AP-1 tethers c-Ets-1 to the TIMP-1 promoter via protein-protein interaction to achieve Ets-dependent transcriptional regulation. Collectively, our results indicate that TIMP-1 expression is controlled by several DNA response elements that respond to variations in the level and activity of AP-1 and Ets transcriptional regulatory proteins.

A constant cathodic potential device for faradic stimulation of osteogenesis

The purpose of this study was to design, develop, and test a device that continuously maintains a constant potential at a cathode with respect to a reference electrode by automatically varying the potential between the cathode and an anode. The ability of the device to maintain a constant cathodic potential with respect to a silver/silver chloride reference electrode is demonstrated in acute testing with a variety of electrodes as well as in chronic testing conducted until battery failure. This constant cathodic potential device permits delivery of current at an optimal cathodic potential for faradic stimulation of osteogenesis which involves a net transfer of charge through biological tissue between, typically, an implanted cathode, the negative electrode where osteogenesis occurs, and either an implanted or a topical anode, the positive electrode required only to complete the electrical circuit. Unlike present devices that maintain a constant direct current between a cathode and an anode but permit potential between said electrodes to vary, this device presents the possible detrimental effects of an undesired electrochemical reaction due to an excessive cathodic potential.

Asymptomatic undetected mediastinal mass: a death during ambulatory anesthesia

T-cell lymphoma is the fastest growing non-Hodgkin's lymphoma occurring in children. Its clinical presentation is frequently abrupt, and total tumor mass can double every few days. At the same time, the number of ambulatory anesthesia procedures for children is increasing at a rapid rate. Anesthesiologists are constantly faced with decisions regarding the adequacy of available preoperative information. What information do we need, and how recent should it be? This case shows that recent diagnostic imaging studies not showing the presence of a mediastinal lymphoma can be misleading. It provides a strong warning to all anesthesiogists involved in ambulatory anesthesia.

Antisense transcripts and protein binding motifs within the Wilms tumour (WT1) locus

Transcription of the WT1 locus is restricted, both temporally and spatially, to a subset of epithelial cells in mammalian kidneys and gonads. WT1, one of the two divergent transcripts mapping to this locus encodes a zinc finger protein that is likely a transcriptional regulator. The other transcript, WIT1, encodes a product of unknown function that is subject to alternate splicing in the region immediately 5' of the WT1 gene. Analysis of the 5' end of this locus further revealed the presence of multiple transcriptional start sites for both genes, such that some of the WIT1 transcripts are encoded by the antisense strand of the first exon of WT1. The genomic region surrounding the transcriptional start sites appears to constitute part of a bi-directional promoter based on the ability of a DNA fragment derived from this region to direct expression of a chimeric CAT gene construct in transient transfection assays. Discrete sequences within the region are capable of interaction in vitro with nuclear extracts derived from a variety of rat and mouse tissues. Interestingly, recombinant WT1, representing the product of zinc finger region of the most abundant of the four alternatively spliced transcripts, is also capable of binding to sequences within this region.