The visual word form area: spatial and temporal characterization of an initial stage of reading in normal subjects and posterior split-brain patients

A standard model of word reading postulates that visual information is initially processed by occipitotemporal areas contralateral to the stimulated hemifield, from whence it is subsequently transferred to the visual word form (VWF) system, a left inferior temporal region specifically devoted to the processing of letter strings. For stimuli displayed in the left visual field, this transfer proceeds from the right to the left hemisphere through the posterior portion of the corpus callosum. In order to characterize the spatial and temporal organization of these processes, reading tasks with split-field presentation were performed by five control subjects and by two patients suffering from left hemialexia following posterior callosal lesions. The subjects' responses were studied using behavioural measures and functional brain imaging techniques, providing both high spatial resolution (functional MRI, fMRI) and high temporal resolution (high-density event-related potentials, ERPs). Early visual processing was revealed as activations contralateral to stimulation, located by fMRI in the inferior occipitotemporal region and presumably coincident with area V4. A negative wave occurring 150-160 ms post-stimulus, also strictly contralateral to stimulation, was recorded over posterior electrodes. In contrast with these hemifield-dependent effects, the VWF system was revealed as a strictly left-hemispheric activation which, in control subjects, was identical for stimuli presented in the left or in the right hemifield and was located in the middle portion of the left fusiform gyrus. The electrical signature of the VWF system consisted of a unilateral sharp negativity, recorded 180-200 ms post-stimulus over left inferior temporal electrodes. In callosal patients, due to the inability of visual information to pass across the posterior part of the corpus callosum, the VWF system was activated only by stimuli presented in the right visual field. Similarly, a significant influence of the word/non-word status on ERPs recorded over the left hemisphere was discernible for either hemifield in controls, while it affected only right-hemifield stimuli in callosal patients. These findings provide direct support for the main components of the classical model of reading and help specify their timing and cerebral substrates.

Modelling of the three-dimensional architecture of group I catalytic introns based on comparative sequence analysis

Alignment of the 87 available sequences of group I self-splicing introns reveals numerous instances of covariation between distant sites. Some of these covariations cannot be ascribed to historical coincidences or the known secondary structure of group I introns, and are, therefore, best explained as reflecting tertiary contacts. With the help of stereochemical modelling, we have taken advantage of these novel interactions to derive a three-dimensional model of the conserved core of group I introns. Two noteworthy features of that model are its extreme compactness and the fact that all of the most evolutionarily conserved residues happen to converge around the two helices that constitute the substrate of the core ribozyme and the site that binds the guanosine cofactor necessary for self-splicing. Specific functional implications are discussed, both with regard to the way the substrate helices are recognized by the core and possible rearrangements of the introns during the self-splicing process. Concerning potential long-range interactions, emphasis is put on the possible recognition of two consecutive purines in the minor groove of a helix by a GAAA or related terminal loop.

Comparative and functional anatomy of group II catalytic introns--a review

The 70 published sequences of group II introns from fungal and plant mitochondria and plant chloroplasts are analyzed for conservation of primary sequence, secondary structure and three-dimensional base pairings. Emphasis is put on structural elements with known or suspected functional significance with respect to self-splicing: the exon-binding and intron-binding sites, the bulging A residue involved in lariat formation, structural domain V and two isolated base pairs, one of them involving the last intron nucleotide and the other one, the first nt of the 3' exon. Separate sections are devoted to the 29 group II-like introns from Euglena chloroplasts and to the possible relationship of catalytic group II introns to nuclear premessenger introns. Alignments of all available sequences of group II introns are provided in the APPENDIX.

Structure and activities of group II introns

Group II introns are found in eubacteria and eubacterial-derived, organellar genomes. They have ribozymic activities, by which they direct and catalyze the splicing of the exons flanking them. This chapter reviews the secondary structure and known tertiary interactions of the ribozymic component of group II introns in relation to the problems of specifying splice sites and building a catalytic core. We pay special attention to the relationship between the transesterification and hydrolytic modes of initiating splicing and the stereospecificities of these reactions. A number of group II introns encode proteins of the reverse transcriptase family; the activity of these proteins enables the host introns to change genomic locations by mechanisms that are only beginning to be deciphered. Finally, we briefly discuss multipartite and post-transcriptionally edited group II introns, together with the intron microcosm of Euglena gracilis chloroplasts and the possible relationships between group II and spliceosome-catalyzed splicing processes.

Comparison of fungal mitochondrial introns reveals extensive homologies in RNA secondary structure

The complete sequences of nine Saccharomyces cerevisiae mitochondrial introns, six of which carry long open reading frames, have already been published. We have recently determined the sequence of an intron in the large ribosomal mitochondrial RNA of Kluyveromyces thermotolerans (Jacquier et al., in preparation), which we found to be closely related to its S. cerevisiae counterpart. This latter result prompted us to undertake a systematic search for possible homologous elements in the other, available sequences with the help of an original computer program. A previously unsuspected wealth of evolutionarily conserved sequences and secondary structures was thus uncovered. Seven at least of the available sequences may be folded up into elaborate secondary structure models, the cores of which are nearly identical. These models result in bringing together the exon-intron junctions into relatively close spatial proximity and looping out either all or most of the sequences in open reading frame, when present. These results and their possible implications with respect to the mechanism of splicing are discussed in the light of available genetic and biochemical data.

Conservation of RNA secondary structures in two intron families including mitochondrial-, chloroplast- and nuclear-encoded members

Two families of fungal mitochondrial introns that include all known sequences have been recognized. These families are now extended to incorporate a plant mitochondrial intron and several introns in chloroplast- and nuclear-encoded rRNA and tRNA precursors. Members of the same family share distinctive sequence stretches and a number of potential RNA secondary structures that would bring these stretches and the intron-exon junctions into relatively close proximity. Using several of these introns which have been extensively studied by either biochemical or genetic means, an attempt is made to integrate the available data into a common picture.

The guanosine binding site of the Tetrahymena ribozyme

The self-splicing Group I introns have a highly specific binding site for the substrate guanosine. Mutant versions of the Tetrahymena ribozyme have been used in combination with guanosine analogues to identify the nucleotide in the ribozyme that is primarily responsible for recognition of the guanine base.

Frequent use of the same tertiary motif by self-folding RNAs

We have identified an 11 nucleotide RNA motif, [CCUAAG...UAUGG], that is extraordinarily abundant in group I and group II self-splicing introns at sites known, or suspected from co-variation analysis, to interact with hairpin terminal loops with a GNRA consensus sequence. Base substitution experiments using a ribozyme-substrate system derived from a group I intron reveal that this motif interacts preferentially with GAAA terminal loops and binds them with remarkable affinity, compared with other known combinations of GNRA loops and matched targets. A copy of the [CCUAAG...UAUGG] motif which is present in domain I of many group II introns is shown to interact with the GAAA terminal loop that caps domain V. This is the first interaction to be identified between these two domains, whose mutual recognition is known to be necessary and sufficient for group II ribozymic activity. We conclude that interaction of [CCUAAG...UAUGG] with GAAA loops is one of the most common solutions used by nature to solve the problem of compacting and bringing together RNA structural domains.

Impairment of grasping movements following a bilateral posterior parietal lesion

The observation of a patient (A.T.) with a bilateral posterior parietal lesion of vascular origin is reported. A.T. presented a bilateral (more marked on the right) deficit in grasping simple objects (neutral cylindrical dowels) without deficit in reaching toward the location of these objects. The major symptom was an exaggerated anticipatory opening of the fingers with poor correlation with object size, resulting in awkward grasps. It was present both when the hand was visible to the subject and when it was not. This deficit was much less marked if the neutral objects were replaced by usual objects of the same sizes. Finally, in tasks where she had to indicate with her fingers the size of visual objects presented as virtual images through a mirror, or the size of imagined usual objects, A.T. performed normally. These results are discussed within the framework of a dual representation of objects. Only the "pragmatic" representation for steering object-oriented actions would be impaired in this patient as a result of posterior parietal damage. By contrast the semantic representation for object identification would be intact.

Quality of life in asthma. I. Internal consistency and validity of the SF-36 questionnaire

Asthma is a chronic disease in which social life is altered. The importance of restrictions on social life may be greater in severe asthma or when symptoms are not adequately controlled. General scales of quality-of-life (QOL) may be used to detect the importance of social life impairment, but it is not yet known whether the scores of such QOL measures are reliable and valid in asthmatic patients. A study was carried out in 252 patients with asthma of variable severity (FEV1 ranging from 25 to 131% of predicted) to assess the validity of a general QOL scale, the first French version of the SF-36 health status questionnaire (SF-36). This is based on 36 items selected to represent nine health concepts (physical, social, and role functioning; mental health; health perceptions; energy or fatigue; pain; and general health). All nine SF-36 category scores were highly significantly correlated with the severity of asthma assessed by the clinical score of Aas (p < 0.0007 to p < 0.0001). Eight SF-36 category scores were highly significantly correlated with FEV1 (p < 0.003 to p < 0.0001). A high internal reliability of SF-36 was found using the alpha coefficient of Cronbach (0.91 for the whole questionnaire). The SF-36 questionnaire is valid and reliable in asthma and can therefore be used to examine QOL in asthmatic and nonasthmatic patients and to determine to what extent asthma impairs social life.

Eosinophilic and neutrophilic inflammation in asthma, chronic bronchitis, and chronic obstructive pulmonary disease

BACKGROUND

Eosinophils but not neutrophils may play a role in the airway inflammation of asthma. In chronic bronchitis (CB) and chronic obstructive pulmonary disease (COPD), neutrophils are present in the airways. To differentiate among the pathology of asthma, CB, and COPD eosinophils and neutrophils were studied in peripheral blood, bronchial biopsy specimens, and bronchoalveolar lavage fluid (BALF).

METHODS

We studied nine nonsmoking healthy subjects, 20 nonsmoking patients with asthma, 10 nonatopic smoking patients with CB (forced expiratory volume in 1 second: 98.4% +/- 11.3%) and 17 patients with COPD (forced expiratory volume in 1 second: 51.2% +/- 14.3%). Eosinophils were characterized by their enumeration in biopsy specimens (EG2 monoclonal antibody), peripheral blood, and BALF and by measurement of eosinophil cationic protein in BALF. Neutrophils were characterized by their enumeration in biopsy specimens (anti-elastase monoclonal antibody) and BALF and by measurement of neutrophil-specific myeloperoxidase in BALF.

RESULTS

In patients with asthma we found degranulated eosinophils in biopsy specimens and significantly increased eosinophil cationic protein levels in BALF. In patients with CB or COPD, eosinophil numbers in biopsy specimens were not significantly different from those of patients with asthma, but cells were not degranulated and eosinophil cationic protein levels in BALF were similar to those of normal subjects. In patients with CB or COPD neutrophils were not increased in the mucosa, but neutrophil numbers and myeloperoxidase levels in BALF were significantly increased.

CONCLUSION

The percentages of neutrophils in BALF were greater in patients with COPD than in those with CB, suggesting a role in the chronic airflow limitation.

New loop-loop tertiary interactions in self-splicing introns of subgroup IC and ID: a complete 3D model of the Tetrahymena thermophila ribozyme

BACKGROUND

Group I introns self-splice via two consecutive trans-esterification reactions in the presence of guanosine cofactor and magnesium ions. Comparative sequence analysis has established that a catalytic core of about 120 nucleotides is conserved in all known group I introns. This core is generally not sufficient for activity, however, and most self-splicing group I introns require non-conserved peripheral elements to stabilize the complete three-dimensional (3D) structure. The physico-chemical properties of group I introns make them excellent systems for unraveling the structural basis of the RNA-RNA interactions responsible for promoting the self-assembly of complex RNAs.

RESULTS

We present phylogenetic and experimental evidence for the existence of three additional tertiary base pairings between hairpin loops within peripheral components of subgroup IC1 and ID introns. Each of these new long range interactions, called P13, P14 and P16, involves a terminal loop located in domain 2. Although domains 2 of IC and ID introns share very strong sequence similarity, their terminal loops interact with domains 5 and 9 (subgroup IC1) and domain 6 (subgroup ID). Based on these tertiary contacts, comparative sequence analysis, and published experimental results such as Fe(II)-EDTA protection patterns, we propose 3D models for two entire group I introns, the subgroup IC1 intron in the large ribosomal precursor RNA of Tetrahymena thermophila and the SdCob.1 subgroup ID intron found in the cytochrome b gene of Saccharomyces douglasii.

CONCLUSIONS

Three-dimensional models of group I introns belonging to four different subgroups are now available. They all emphasize the modular and hierarchical organization of the architecture of group I introns and the widespread use of base-pairings between terminal hairpin loops for stabilizing the folded and active structures of large and complex RNA molecules.

Brain regions involved in the perception of gaze: a PET study

Mutual gaze may be described as a psychological process during which two persons have the feeling of a brief link between their two minds. In the monkey, specific cell assemblies in the superior temporal cortex of the brain are responsive to gaze. This suggests that the brain may have evolved mechanisms for interpreting direct eye contact. These mechanisms could depend on the activation of specific brain regions. Positron emission tomography was used to measure activity in brain regions in healthy volunteers while they were looking at faces featuring, respectively, eye contact, averted gaze, or no gaze. As expected a region known to be involved in face processing was found to be activated in the ventral occipito-temporal region, especially in the right hemisphere. Averted gaze and mutual gaze triggered blood flow responses in similar areas which were different from those involved in face processing. These areas included the occipital part of the fusiform gyrus, the right parietal lobule, the right inferior temporal gyrus, and the middle temporal gyrus in both hemispheres. These results are consistent with the hypothesis that perception of eyes regardless of the direction of the gaze is subserved by a distributed network. However, no conclusive evidence was found for specific area(s) devoted to mutual gaze processing.

Mitochondrial class II introns encode proteins related to the reverse transcriptases of retroviruses

Organelle introns share several distinctive features that set them apart from their counterparts in nuclear-encoded pre-messenger RNAs (reviewed in ref. 1): their termini do not obey the GU...AG rule; the introns are 'structured' (members of the same family or 'class' can theoretically adopt very similar RNA secondary conformations and several of the postulated pairings have been confirmed by studies of splicing mutants and their revertants (see, for example, ref. 4); many introns from both classes contain long open reading frames. We report here that the proteins potentially encoded by four class II introns are related to several RNA-dependent polymerases of viral and transposable element origins.

Comparative analysis of actual and mental movement times in two graphic tasks

This study compared the temporal organization of graphic movements executed either actually or mentally. Six subjects had to perform two tasks, writing a sentence and drawing a cube, either as a real performance or as an imagined one, with either the right or the left hand, and with either a small or a large tracing amplitude. In the same subject, for the same hand, mental and actual movement times were both very stable and very close from trial to trial regardless of the tracing amplitude. Thus, mental movements mimic closely real movements in their temporal organization and are likely to involve the same planning program.

Comparison of cord blood immunoglobulin E concentrations and maternal allergy for the prediction of atopic diseases in infancy

Total serum IgE levels were determined in 136 newborns and their mothers and in 54 of their fathers, using the paper radioimmunosorbent test (PRIST) technique. IgE specific antibodies for house dust (Dermatophagoides pteronyssinus), orchard grass, timothy grass, and cow's milk were measured with the radioallergosorbent test (RAST). One hundred thirty-three RAST assays were negative in newborns, and in three cases RAST for cow's milk was positive. Cord blood IgE ranged from 0 to 5.5 IU/ml (mean 0.32 +/- 0.54 IU/ml); levels were significantly (p less than 0.05) higher when maternal IgE was over 100 IU/ml and when mothers had received progesterone therapy during the pregnancy. Salbutamol administration or tobacco smoking during pregnancy did not influence newborn IgE. A clinical follow-up study was conducted in 83 infants for 9 mo. Nine infants developed definite atopic disease, and possible allergic diseases were noted in eight other infants. The IgE level at birth appeared to be more predictive for the development of allergy in infancy than the family history.

Involvement of a GNRA tetraloop in long-range RNA tertiary interactions

Terminal loops with a GNRA consensus sequence are widespread in RNA. It has been suggested that these loops act as "anchors" during tertiary folding, by interacting in a sequence-specific way with helices at distant locations along the molecule. We now show that a GUGA loop changes state upon disruption of the tertiary architecture of a self-splicing group I intron. Successful replacement of the postulated loop-helix contact by classical base-pairing points to binding of the loop into the shallow (minor) groove of the helix, as also indicated by partial restoration of ribozyme stability upon a specific double nucleotide substitution.

Group II self-splicing introns in bacteria

Like nuclear premessenger introns, group II self-splicing introns are excised from primary transcripts as branched molecules, containing a 2'-5' phosphodiester bond. For this reason, it is widely believed that the ribozyme (catalytic RNA) core of group II introns, or some evolutionarily related molecule, gave rise to the RNA components of the spliceosomal splicing machinery of the eukaryotic nucleus. One difficulty with this hypothesis has been the restricted distribution of group II introns. Unlike group I self-splicing introns, which interrupt not only organelle primary transcripts, but also some bacterial and nuclear genes, group II introns seemed to be confined to mitochondrial and chloroplast genomes (reviewed in ref. 6). We now report the discovery of group II introns both in cyanobacteria (the ancestors of chloroplasts) and the gamma subdivision of purple bacteria, or proteobacteria, whose alpha subdivision probably gave rise to mitochondria. At least one of these introns actually self-splices in vitro.

Double-blind, placebo-controlled rush immunotherapy with a standardized Alternaria extract

Specific immunotherapy is ineffective with unstandardized mold extracts. A double-blind, placebo-controlled study was performed in 24 patients (5 to 56 years of age) only allergic to Alternaria. The extract was standardized by isoelectric focusing, crossed immunoelectrophoresis, crossed radioimmunoelectrophoresis, RAST inhibition, and skin tests and contained allergen Alternaria major allergen a I and antigen B. Thirteen patients received the active treatment, and 11 received the placebo. Immunotherapy was started by a 2-day rush protocol; maintenance injections were administered for 1 year. The patient's self-evaluation of the treatment was significantly (p less than 0.001) lower in the placebo-treated group. Global symptom-medication scores, including asthma and rhinoconjunctivitis, were significantly (p less than 0.005) lower in the actively treated group. Nasal challenges with Alternaria extract were performed before immunotherapy and after 1 year of treatment. There was no difference in the placebo-treated group and a significantly (p less than 0.01) increased mean provocative dose in the actively treated group. Skin tests were significantly reduced in the actively treated group. Specific IgG increased significantly in the actively treated group and were stable in the placebo-treated group. There was a significant correlation between nasal challenges and nasal symptom-medication scores (p less than 0.03) or the patient's self-evaluation of efficacy (p less than 0.05). This study demonstrated that patients only sensitized to Alternaria benefit from specific immunotherapy with a standardized Alternaria extract.

Multiple exon-binding sites in class II self-splicing introns

Partial deletion of the exon 5' to S. cerevisiae intron a5, a self-splicing mitochondrial class II intron, reveals the existence of several sites of intron-exon interaction. We have identified two of the corresponding exon-binding sites in intron a5 by comparative sequence analysis and RNAase H digestion of the intron complexed to a DNA version of its 5' exon. Introduction of mutations in either the intronic sites or the complementary exonic sequences affects splicing in vitro, whereas double mutants in which intron-exon pairings have been restored show normal activity. Some of the mutants accumulate a product that was shown to be the intron-3' exon lariat, a postulated splicing intermediate. The possible role of one of the intronic sites in aligning exons for the ligation step is discussed.

A paradoxical improvement of misreaching in optic ataxia: new evidence for two separate neural systems for visual localization

We tested a patient (A. T.) with bilateral brain damage to the parietal lobes, whose resulting 'optic ataxia' causes her to make large pointing errors when asked to locate single light emitting diodes presented in her visual field. We report here that, unlike normal individuals, A. T.'s pointing accuracy improved when she was required to wait for 5 s before responding. This counter-intuitive result is interpreted as reflecting the very brief time-scale on which visuomotor control systems in the superior parietal lobe operate. When an immediate response was required, A. T.'s damaged visuomotor system caused her to make large errors; but when a delay was required, a different, more flexible, visuospatial coding system--presumably relatively intact in her brain--came into play, resulting in much more accurate responses. The data are consistent with a dual processing theory whereby motor responses made directly to visual stimuli are guided by a dedicated system in the superior parietal and premotor cortices, while responses to remembered stimuli depend on perceptual processing and may thus crucially involve processing within the temporal neocortex.

Computed tomography of the lungs in asthma: influence of disease severity and etiology

Airways remodelling is a feature of longstanding asthma, but may differ in persons with allergic and nonallergic asthma. To assess airways remodelling indirectly, we compared permanent CT-scan abnormalities in 70 subjects with allergic (median age: 30 yr) and 56 with nonallergic asthma (median age: 54.5 yr) who had had asthma of similar duration. None of the subjects were smokers. Asthma severity was assessed by Aas score and FEV1. Permanent high-resolution computed tomographic (HR-CT) scan abnormalities were characterized. In comparison with allergic asthmatic subjects, those with nonallergic asthma had a significantly greater frequency of cylindric (p < 0.0007, Mann-Whitney U test) and varicose (p < 0.004) bronchiectasis, emphysema (p < 0.0003), bronchial recruitment (p < 0.0001), and sequellar linear shadows (p < 0.0001). There was a significant correlation between Aas score and emphysema (p < 0.0001 for nonallergic and p < 0.0005 for allergic asthma; Kendall's test method) or Aas score and sequellar linear shadows (p < 0.007, nonallergic asthma). There was a significant increase in the extent of permanent abnormalities with increasing severity and duration of asthma in both groups. Patients with brittle asthma had few permanent abnormalities. This study confirms that after a similar course of the disease, patients with nonallergic asthma have a more extensive remodelling of the airways than those with allergic asthma.

p95vav associates with tyrosine-phosphorylated SLP-76 in antigen-stimulated T cells

p95vav, the product of the vav protooncogene, has been implicated in the T cell receptor (TCR)-mediated signaling cascade p95vav is phosphorylated on tyrosine residues after TCR stimulation by anti-TCR/CD3 antibodies and possesses a number of landmark features of signaling molecules such as a putative guanine nucleotide exchange factor domain, a pleckstrin homology domain, and an Sre homology (SH) 2 and two SH3 domains, which provide the capacity to form multimeric signaling complexes. However, the precise role of p95vav in TCR signaling remains unclear. In this work we show that physiological stimulation of T cell hybridomas with antigen presented by major histocompatibility complex class II molecules leads to a strong tyrosine phosphorylation of p95vav and its association with tyrosine-phosphorylated SLP-76. SLP-76 is a newly described SH2-containing protein that has been previously found to bind to the adapter molecule Grb2. Moreover, we provide evidence that p95vav-SI P-76 association is SH2-mediated by demonstrating that this interaction can be inhibited by a phosphopeptide containing a putative p95vav-SH2-binding motif (pYESP) present in SLP-76. Furthermore, in vitro experiments show that after antigen stimulation, phosphorylated p95vav-SLP-76 can bind to Grb2 in a complex that contains pp36/38 and pp116 proteins. Our data provide a clue to explain recent independent observations that overexpression of p95vav or SLP-76 enhances TCR-mediated gene activation.

Physicochemical modifications of high-pressure-treated soybean protein isolates

Changes induced by high pressure (HP) treatment (200-600 MPa) on soybean protein isolates (SPI) at pH 3 (SPI3) and pH 8 (SPI8) were analyzed. Changes in protein solubility, surface hydrophobicity (Ho), and free sulfhydryl content (SH(F)) were determined. Protein aggregation and denaturation and changes in secondary structure were also studied. An increase in protein Ho and aggregation, a reduction of free SH, and a partial unfolding of 7S and 11S fractions were observed in HP-treated SPI8. Changes in secondary structure were also detected, which led to a more disordered structure. HP-treated SPI3 was partially denatured and presented insoluble aggregates. A major molecular unfolding, a decrease of thermal stability, and an increase of protein solubility and Ho were also detected. At 400 and 600 MPa, a decrease of the SH(F) and a total denaturation were observed.