Low codon bias and high rates of synonymous substitution in Drosophila hydei and D. melanogaster histone genes

We have evaluated codon usage bias in Drosophila histone genes and have obtained the nucleotide sequence of a 5,161-bp D. hydei histone gene repeat unit. This repeat contains genes for all five histone proteins (H1, H2a, H2b, H3, and H4) and differs from the previously reported one by a second EcoRI site. These D. hydei repeats have been aligned to each other and to the 5.0-kb (i.e., long) and 4.8-kb (i.e., short) histone repeat types from D. melanogaster. In each species, base composition at synonymous sites is similar to the average genomic composition and approaches that in the small intergenic spacers of the histone gene repeats. Accumulation of synonymous changes at synonymous sites after the species diverged is quite high. Both of these features are consistent with the relatively low codon usage bias observed in these genes when compared with other Drosophila genes. Thus, the generalization that abundantly expressed genes in Drosophila have high codon bias and low rates of silent substitution does not hold for the histone genes.      

Lack of Liver X Receptors Leads to Cell Proliferation in a Model of Mouse Dorsal Prostate Epithelial Cell

Recent studies underline the implication of Liver X Receptors (LXRs) in several prostate diseases such as benign prostatic hyperplasia (BPH) and prostate cancer. In order to understand the molecular mechanisms involved, we derived epithelial cells from dorsal prostate (MPECs) of wild type (WT) or Lxrαβ−/− mice. In the WT MPECs, our results show that LXR activation reduces proliferation and correlates with the modification of the AKT-survival pathway. Moreover, LXRs regulate lipid homeostasis with the regulation of Abca1, Abcg1 and Idol, and, in a lesser extent, Srebp1, Fas and Acc. Conversely cells derived from Lxrαβ−/− mice show a higher basal phosphorylation and consequently activation of the survival/proliferation transduction pathways AKT and MAPK. Altogether, our data point out that the cell model we developed allows deciphering the molecular mechanisms inducing the cell cycle arrest. Besides, we show that activated LXRs regulate AKT and MAPK transduction pathways and demonstrate that LXRs could be good pharmacological targets in prostate disease such as cancer.     

Phosphorylation of the kinase suppressor of ras by associated kinases

The kinase suppressor of Ras (KSR) is a loss-of-function allele that suppresses the rough eye phenotype of activated Ras in Drosophila and the multivulval phenotype of activated Ras in Caenorhabditis elegans. The physiological role of mammalian KSR is not known. We examined the mechanisms regulating the phosphorylation of this putative kinase in mammalian cells. Wild-type mouse KSR and a mutated KSR protein predicted to create a kinase-dead protein are phosphorylated identically in intact cells and in the immune complex. Phosphopeptide sequencing identified 10 in vivo phosphorylation sites in KSR, all of which reside in the 539 noncatalytic amino terminal amino acids. Expression of the amino terminal portion of KSR alone demonstrated that it was phosphorylated in the intact cell and in an immune complex in a manner indistinguishable from that of intact KSR. These data demonstrate that the kinase domain of KSR is irrelevant to its phosphorylation state and suggest that the phosphorylation of KSR and its association with a distinct set of kinases may affect intracellular signaling.     

α1β1-Integrin is an essential signal for neurite outgrowth induced by thrombospondin type 1 repeats of SCO-spondin

In the central and peripheral nervous systems a heterogeneous group of proteins constituting the thrombospondin superfamily provides a cue for axonal pathfinding. They either contain or are devoid of the tripeptide RGD, and the sequence(s) and mechanism(s) which trigger in vitro their neurite-promoting activity have remained unclear. In this study, we reconsider the problem of whether sequences present in the thrombospondin type 1 repeats (TSRs), and independent of the well-known RGD-binding site, may activate integrins and account for their neurite-promoting activity. SCO-spondin is a newly identified member of the thrombospondin superfamily, which shows a multidomain organization with a great number of TSR motifs but no RGD sequence. Previous research has implicated oligopeptides derived from SCO-spondin TSRs in in-vitro development of various neuronal cell types. In this study, we investigate whether function-blocking antibodies directed against integrin subunits can block these effects in cell line B104, cloned from a neuroblastoma of the rat central nervous system. By two different approaches: flow cytometry revealing short-term effects and cell cultures revealing long-term effects, we show that: (a) activation of cell metabolism, (b) changes in cell size and structure, and (c) neurite-promoting activity induced by TSR oligopeptides are inhibited by function-blocking antibodies to 1-subunit. Using a panel of function-blocking antibodies directed against various integrin -subunits we show that the 1-subunit might be the partner of the 1-subunit in B104 cells. Thus, we demonstrate that an original sequence within a TSR motif from SCO-spondin promotes neurite outgrowth through an intracellular signal driven by integrins, independently of an RGD-binding site.     

Direct intracranial, FMRI, and lesion evidence for the causal role of left inferotemporal cortex in reading

Models of the "visual word form system" postulate that a left occipitotemporal region implements the automatic visual word recognition required for efficient reading. This theory was assessed in a patient in whom reading was explored with behavioral measures, fMRI, and intracranial local field potentials. Prior to surgery, when reading was normal, fMRI revealed a normal mosaic of ventral visual selectivity for words, faces, houses, and tools. Intracranial recordings demonstrated that the left occipitotemporal cortex responded with a short latency to conscious but also to subliminal words. Surgery removed a small portion of word-responsive occipitotemporal cortex overlapping with the word-specific fMRI activation. The patient developed a marked reading deficit, while recognition of other visual categories remained intact. Furthermore, in the post-surgery fMRI map of visual cortex, only word-specific activations disappeared. Altogether, these results provide direct evidence for the causal role of the left occipitotemporal cortex in the recognition of visual words.     

The molecular scaffold kinase suppressor of Ras 1 is a modifier of RasV12-induced and replicative senescence

In primary mouse embryo fibroblasts (MEFs), oncogenic Ras induces growth arrest via Raf/MEK/extracellular signal-regulated kinase (ERK)-mediated activation of the p19ARF/p53 and INK4/Rb tumor suppressor pathways. Ablation of these same pathways causes spontaneous immortalization in MEFs, and oncogenic transformation by Ras requires ablation of one or both of these pathways. We show that Kinase Suppressor of Ras 1 (KSR1), a molecular scaffold for the Raf/MEK/ERK cascade, is necessary for RasV12-induced senescence, and its disruption enhances primary MEF immortalization. RasV12 failed to induce p53, p19ARF, p16INK4a, and p15INK4b expression in KSR1-/- MEFs and increased proliferation instead of causing growth arrest. Reintroduction of wild-type KSR1, but not a mutated KSR1 construct unable to bind activated ERK, rescued RasV12-induced senescence. On continuous culture, deletion of KSR1 accelerated the establishment of spontaneously immortalized cultures and increased the proportion of cultures escaping replicative crisis. Despite enhancing escape from both RasV12-induced and replicative senescence, however, both primary and immortalized KSR1-/- MEFs are completely resistant to RasV12-induced transformation. These data show that escape from senescence is not necessarily a precursor for oncogenic transformation. Furthermore, these data indicate that KSR1 is a member of a unique class of proteins whose deletion blocks both senescence and transformation.     

Similar or Different? The Role of the Ventrolateral Prefrontal Cortex in Similarity Detection

Patients with frontal lobe syndrome can exhibit two types of abnormal behaviour when asked to place a banana and an orange in a single category: some patients categorize them at a concrete level (e.g., "both have peel"), while others continue to look for differences between these objects (e.g., "one is yellow, the other is orange"). These observations raise the question of whether abstraction and similarity detection are distinct processes involved in abstract categorization, and that depend on separate areas of the prefrontal cortex (PFC). We designed an original experimental paradigm for a functional magnetic resonance imaging (fMRI) study involving healthy subjects, confirming the existence of two distinct processes relying on different prefrontal areas, and thus explaining the behavioural dissociation in frontal lesion patients. We showed that: 1) Similarity detection involves the anterior ventrolateral PFC bilaterally with a right-left asymmetry: the right anterior ventrolateral PFC is only engaged in detecting physical similarities; 2) Abstraction per se activates the left dorsolateral PFC.     

Caveolin-1 Is Required for Kinase Suppressor of Ras 1 (KSR1)-Mediated Extracellular Signal-Regulated Kinase 1/2 Activation,H-RasV12-Induced Senescence,and Transformation

The molecular scaffold kinase suppressor of Ras 1 (KSR1) regulates the activation of the Raf/MEK/extracellular signal-regulated kinase (ERK) signal transduction pathway. KSR1 disruption in mouse embryo fibroblasts (MEFs) abrogates growth factor-induced ERK activation, H-Ras^V12-induced replicative senescence, and H-Ras^V12-induced transformation. Caveolin-1 has been primarily described as a major component of the coating structure of caveolae, which can serve as a lipid binding adaptor protein and coordinates the assembly of Ras, Raf, MEK, and ERK. In this study, we show that KSR1 interacts with caveolin-1 and is responsible for MEK and ERK redistribution to caveolin-1-rich fractions. The interaction between KSR1 and caveolin-1 is essential for optimal activation of ERK as a KSR1 mutant unable to interact with caveolin-1 does not efficiently mediate growth factor-induced ERK activation at the early stages of pathway activation. Furthermore, abolishing the KSR1–caveolin-1 interaction increases growth factor demands to promote H-Ras^V12-induced proliferation and has adverse effects on H-Ras^V12-induced cellular senescence and transformation. These data show that caveolin-1 is necessary for optimal KSR1-dependent ERK activation by growth factors and oncogenic Ras.     

Reproducibility of plasma catecholamine concentrations at rest and during exercise in man

The purpose of this study was to test the reproducibility of plasma norepinephrine (NE) and epinephrine (E) concentrations, at rest and during exercise, in man. Twelve young men were evaluated on two occasions (one week apart) at rest in supine and sitting positions and during dynamic exercise on bicycle ergometer: 5 min at a low intensity workload (heart rate = 131-133 bt min-1) and 5 and 20 min at a higher intensity (174-175 bt min-1). Mean plasma NE and E concentrations were not significantly different (p less than 0.05) on the two occasions in any of the experimental situations. However large within-subject variations were present, and the "standard errors of a single measurement" corrected for the variability of the catecholamine assay, ranged from 14 to 50% for NE and 14 to 37% for E. These results indicate that the mean plasma NE and E concentrations observed in a group of subjects are reproducible from one week to the other, but that individual plasma NE and E concentrations are not. This lack of reliability of a single determination of plasma catecholamine concentrations might be due to cyclic variations of plasma NE and E concentrations over time.