De Novo Variants Found in Three Distinct Schizophrenia Populations Hit a Common Core Gene Network Related to Microtubule and Actin Cytoskeleton Gene Ontology Classes

Schizophrenia (SZ) is a heterogeneous and debilitating psychiatric disorder with a strong genetic component. To elucidate functional networks perturbed in schizophrenia, we analysed a large dataset of whole-genome studies that identified SNVs, CNVs, and a multi-stage schizophrenia genome-wide association study. Our analysis identified three subclusters that are interrelated and with small overlaps: GO:0007017~Microtubule-Based Process, GO:00015629~Actin Cytoskeleton, and GO:0007268~SynapticTransmission. We next analysed three distinct trio cohorts of 75 SZ Algerian, 45 SZ French, and 61 SZ Japanese patients. We performed Illumina HiSeq whole-exome sequencing and identified de novo mutations using a Bayesian approach. We validated 88 de novo mutations by Sanger sequencing: 35 in French, 21 in Algerian, and 32 in Japanese SZ patients. These 88 de novo mutations exhibited an enrichment in genes encoding proteins related to GO:0051015~actin filament binding (p = 0.0011) using David, and enrichments in GO: 0003774~transport (p = 0.019) and GO:0003729~mRNA binding (p = 0.010) using Amigo. One of these de novo variant was found in CORO1C coding sequence. We studied Coro1c haploinsufficiency in a Coro1c+/- mouse and found defects in the corpus callosum. These results could motivate future studies of the mechanisms surrounding genes encoding proteins involved in transport and the cytoskeleton, with the goal of developing therapeutic intervention strategies for a subset of SZ cases.

BigNeuron: a resource to benchmark and predict performance of algorithms for automated tracing of neurons in light microscopy datasets

BigNeuron is an open community bench-testing platform with the goal of setting open standards for accurate and fast automatic neuron tracing. We gathered a diverse set of image volumes across several species that is representative of the data obtained in many neuroscience laboratories interested in neuron tracing. Here, we report generated gold standard manual annotations for a subset of the available imaging datasets and quantified tracing quality for 35 automatic tracing algorithms. The goal of generating such a hand-curated diverse dataset is to advance the development of tracing algorithms and enable generalizable benchmarking. Together with image quality features, we pooled the data in an interactive web application that enables users and developers to perform principal component analysis, t-distributed stochastic neighbor embedding, correlation and clustering, visualization of imaging and tracing data, and benchmarking of automatic tracing algorithms in user-defined data subsets. The image quality metrics explain most of the variance in the data, followed by neuromorphological features related to neuron size. We observed that diverse algorithms can provide complementary information to obtain accurate results and developed a method to iteratively combine methods and generate consensus reconstructions. The consensus trees obtained provide estimates of the neuron structure ground truth that typically outperform single algorithms in noisy datasets. However, specific algorithms may outperform the consensus tree strategy in specific imaging conditions. Finally, to aid users in predicting the most accurate automatic tracing results without manual annotations for comparison, we used support vector machine regression to predict reconstruction quality given an image volume and a set of automatic tracings.

Chr21 protein-protein interactions: enrichment in proteins involved in intellectual disability, autism, and late-onset Alzheimer's disease

Down syndrome (DS) is caused by human chromosome 21 (HSA21) trisomy. It is characterized by a poorly understood intellectual disability (ID). We studied two mouse models of DS, one with an extra copy of the <i>Dyrk1A</i> gene (189N3) and the other with an extra copy of the mouse Chr16 syntenic region (Dp(16)1Yey). RNA-seq analysis of the transcripts deregulated in the embryonic hippocampus revealed an enrichment in genes associated with chromatin for the 189N3 model, and synapses for the Dp(16)1Yey model. A large-scale yeast two-hybrid screen (82 different screens, including 72 HSA21 baits and 10 rebounds) of a human brain library containing at least 10⁷ independent fragments identified 1,949 novel protein-protein interactions. The direct interactors of HSA21 baits and rebounds were significantly enriched in ID-related genes (<i>P</i>-value &lt; 2.29 × 10^-8). Proximity ligation assays showed that some of the proteins encoded by HSA21 were located at the dendritic spine postsynaptic density, in a protein network at the dendritic spine postsynapse. We located HSA21 DYRK1A and DSCAM, mutations of which increase the risk of autism spectrum disorder (ASD) 20-fold, in this postsynaptic network. We found that an intracellular domain of DSCAM bound either DLGs, which are multimeric scaffolds comprising receptors, ion channels and associated signaling proteins, or DYRK1A. The DYRK1A-DSCAM interaction domain is conserved in <i>Drosophila</i> and humans. The postsynaptic network was found to be enriched in proteins associated with ARC-related synaptic plasticity, ASD, and late-onset Alzheimer's disease. These results highlight links between DS and brain diseases with a complex genetic basis.

Looking beyond the usual suspects: sulfide stress in schizophrenia pathophysiology

Schizophrenia is a complex, multifactorial disease that displays heterogeneous behavioral and cognitive syndrome (Lieberman & First, 2018). The origin of schizophrenia appears to lie in genetic and/or environmental disruption of brain development (Owen et al, 2016). In spite of current treatment that largely consists in antipsychotic drugs combined with psychological therapies, social support, and rehabilitation, developing more effective therapeutic interventions is an essential issue.

HENA, heterogeneous network-based data set for Alzheimer's disease

Alzheimer's disease and other types of dementia are the top cause for disabilities in later life and various types of experiments have been performed to understand the underlying mechanisms of the disease with the aim of coming up with potential drug targets. These experiments have been carried out by scientists working in different domains such as proteomics, molecular biology, clinical diagnostics and genomics. The results of such experiments are stored in the databases designed for collecting data of similar types. However, in order to get a systematic view of the disease from these independent but complementary data sets, it is necessary to combine them. In this study we describe a heterogeneous network-based data set for Alzheimer's disease (HENA). Additionally, we demonstrate the application of state-of-the-art graph convolutional networks, i.e. deep learning methods for the analysis of such large heterogeneous biological data sets. We expect HENA to allow scientists to explore and analyze their own results in the broader context of Alzheimer's disease research.

Netrin G1: its downregulation in the nucleus accumbens of cocaine-conditioned mice and genetic association in human cocaine dependence

Netrin G1 is a presynaptic ligand involved in axonal projection. Although molecular mechanisms underlying cocaine addiction are still poorly understood, Netrin G1 might have a role as a regulator of anxiety, fear and spatial memory, behavioural traits impaired in the context of cocaine exposure. In this study, the Netrin G1 (Ntng1) expression was investigated in the nucleus accumbens of mice primarily conditioned to cocaine using a place preference paradigm. A genetic association study was then conducted on 146 multiplex families of the Collaborative study on Genetics of Alcoholism, in which seven single nucleotide polymorphisms located in the NTNG1 gene were genotyped. NTNG1 expression levels were also quantified in BA10, BA46 and the cerebellum of healthy controls (with no Axis 1 psychopathology). Decreased Ntng1 expression was initially observed in the nucleus accumbens of mice conditioned to cocaine. Significant genetic family-based associations were detected between NTNG1 polymorphisms and cocaine dependence. NTNG1 expression in BA10, BA46 and the cerebellum, however, were not significantly associated with any allele or haplotype of this gene. These results confirm that Ntng1 expression is disturbed in the nucleus accumbens of mice, after cocaine conditioning. A haplotype of NTNG1 was found to constitute a vulnerability factor for cocaine use disorder in patients, although none of its single nucleotide polymorphisms were associated with a differential expression pattern in healthy controls. The data suggest that change in the Ntng1 expression is a consequence of cocaine exposure, and that some of its genetic markers are associated with a greater risk for cocaine use disorder.

Fluorescent nanodiamond tracking reveals intraneuronal transport abnormalities induced by brain-disease-related genetic risk factors

Brain diseases such as autism and Alzheimer's disease (each inflicting >1% of the world population) involve a large network of genes displaying subtle changes in their expression. Abnormalities in intraneuronal transport have been linked to genetic risk factors found in patients, suggesting the relevance of measuring this key biological process. However, current techniques are not sensitive enough to detect minor abnormalities. Here we report a sensitive method to measure the changes in intraneuronal transport induced by brain-disease-related genetic risk factors using fluorescent nanodiamonds (FNDs). We show that the high brightness, photostability and absence of cytotoxicity allow FNDs to be tracked inside the branches of dissociated neurons with a spatial resolution of 12 nm and a temporal resolution of 50 ms. As proof of principle, we applied the FND tracking assay on two transgenic mouse lines that mimic the slight changes in protein concentration (∼30%) found in the brains of patients. In both cases, we show that the FND assay is sufficiently sensitive to detect these changes.

Somatostatin-IRES-Cre Mice: Between Knockout and Wild-Type?

The neuropeptide somatostatin (SOM) is widely expressed in rodent brain and somatostatin-IRES-Cre (SOM-cre) mouse strains are increasingly used to unravel the physiology of SOM-containing neurons. However, while knock-in targeting strategy greatly improves Cre-Lox system accuracy, recent reports have shown that genomic insertion of Cre construct per se can markedly affect physiological function. We show that Cre transgene insertion into the 3'UTR of the somatostatin gene leads to the selective and massive depletion of endogenous SOM in all tested brain regions. It also strongly impacts SOM-related neuroendocrine responses in a similar manner to what has been reported for SST KO mice: increased corticosterone levels after 30-min restraint stress, decreased amplitude and regularity of ultradian growth hormone secretory patterns accompanied by changes in sexually dimorphic liver gene expression (serpina1, Cyp2b9, Cyp2a4, Cyp2d9, and Cyp7b1). In addition to demonstrating the need for examination of the consequences of Cre transgenesis, these results also reveal how this SOM-cre strain may be a useful tool in studying the functional consequences of moderate to low SOM levels as reported in neurological and psychiatric disorders.

Single KTP nanocrystals as second-harmonic generation biolabels in cortical neurons

We report an efficient colloidal synthesis of KTiOPO4 (KTP) nanocrystals with excellent crystallinity and the direct observation of optical second-harmonic generation (SHG) from discrete KTP nanocrystals in neurons cultured from mammalian brain cortex. Direct internalization and monitoring of these nanoparticles was successfully achieved without limitations from cytotoxicity, bleaching and blinking emission.

A Disc1 mutation differentially affects neurites and spines in hippocampal and cortical neurons

A balanced chromosomal translocation segregating with schizophrenia and affective disorders in a large Scottish family disrupting DISC1 implicated this gene as a susceptibility gene for major mental illness. Here we study neurons derived from a genetically engineered mouse strain with a truncating lesion disrupting the endogenous Disc1 ortholog. We provide a detailed account of the consequences of this mutation on axonal and dendritic morphogenesis as well as dendritic spine development in cultured hippocampal and cortical neurons. We show that the mutation has distinct effects on these two types of neurons, supporting a cell-type specific role of Disc1 in establishing structural connections among neurons. Moreover, using a validated antibody we provide evidence indicating that Disc1 localizes primarily to Golgi apparatus-related vesicles. Our results support the notion that in vitro cultures derived from Disc1(Tm1Kara) mice provide a valuable model for future mechanistic analysis of the cellular and biochemical effects of this mutation, and can thus serve as a platform for drug discovery efforts.

Neurobiology of attention deficit/hyperactivity disorder

Attention deficit/hyperactivity disorder (ADHD), a prevalent neurodevelopmental disorder, has been associated with various structural and functional CNS abnormalities but findings about neurobiological mechanisms linking genes to brain phenotypes are just beginning to emerge. Despite the high heritability of the disorder and its main symptom dimensions, common individual genetic variants are likely to account for a small proportion of the phenotype's variance. Recent findings have drawn attention to the involvement of rare genetic variants in the pathophysiology of ADHD, some being shared with other neurodevelopmental disorders. Traditionally, neurobiological research on ADHD has focused on catecholaminergic pathways, the main target of pharmacological treatments. However, more distal and basic neuronal processes in relation with cell architecture and function might also play a role, possibly accounting for the coexistence of both diffuse and specific alterations of brain structure and activation patterns. This article aims to provide an overview of recent findings in the rapidly evolving field of ADHD neurobiology with a focus on novel strategies regarding pathophysiological analyses.

SMARCA2 common variant association and rare variant excess in Schizophrenia patients from an Algerian Trio Cohort

Genome wide association studies (GWAS) of Schizophrenia (SZ) patients have identified common variants in ten genes including SMARCA2 (Koga et al., HMG, 2009). We found that the SZ-GWAS genes are part of an interacting network centered on SMARCA2 (Loe-Mie et al., HMG, 2010). Furthermore, SMARCA2 was found disrupted in SZ (Walsh et al., Science, 2008). SMARCA2 encodes the ATPase (BRM) of the SWI/SNF chromatin remodeling complex that is at the interface of genome and environmental adaptation.

Taking advantage of an Algerian trio cohort of one hundred SZ patients (Benmessaoud et al., BMC Psychiatry, 2008), we replicated the association of SNP rs2296212 localized in exon 33, already shown associated in Koga study and resulting in D1546E amino acid change in the SMARCA2 protein. We studied SMARCA2 codons and found that exon 33 displays a signature of positive evolution in the primate lineage.

Our working hypothesis is that the coding regions displaying positive selection are target of novel rare variants. To address this question, we sequenced two exons displaying positive evolution and one exon without evidence of positive evolution.

We found (i) that rare variants are significantly in excess in SZ-patients compared to their parents (p = 0.038, Fisher test) and (ii) a higher proportion of rare variants in the primate-accelerated exons compared with the non-evolutionary exon in SZ-patients (p = 0.032, Fisher test).

SMARCA2 exon sequencing and whole exome sequencing from patients harboring SNP rs2296212 common variant are under progress. Altogether, these results are expected to give new insights into the genetic architecture of SZ.

[Neurobiology of attention deficit/hyperactivity disorder]

Attention deficit/hyperactivity disorder (ADHD) is a frequent and disabling condition in school children, with cognitive and behavioral symptoms persisting into adulthood in a majority of patients. Etiology of ADHD is considered multifactorial and heterogenous, with an important contribution of genetic factors. Apart from genetic risk factors, emphasis has been put on the early environment, and prenatal exposure to nicotine, alcohol, prematurity and low birth weight have been associated with subsequent ADHD symptoms. This article reviews recent findings in neurobiology, genetics and neuroimaging of ADHD. Despite their clinical heterogeneity and frequent comorbidities, key symptoms of ADHD, such as impulsivity, hyperactivity and inattention are regularly improved by dopaminergic agonists, leading to consider dopaminergic dysfunction a possibly contributing factor in ADHD. Norepinephrine agonists also have clinical efficacy on ADHD symptoms and several other neurotransmission systems are likely involved in the etiology of ADHD. Dysfunction of neurotransmitter systems have been related to impairments of sustained attention, inhibitory control and working memory. Cognitive tasks focusing on reaction time and verbal working memory fit certain criteria for ADHD endophenotypes, offering a pathway to bridge the gap between observed traits and genetic vulnerability. Despite ADHD being a highly heritable disorder, most candidate genes with replicated findings across association studies only account for a small proportion of genetic variance. Neuroimaging studies using treatment effect or cognitive tasks show differential activation patterns in ADHD patients, with trends towards normalization under treatment. Further insight into neurobiological mechanisms involved in ADHD will arise from collaborative networks and combination of imaging, genetic and neurobiological techniques with consideration of the developmental aspects of ADHD.

SMARCA2 and other genome-wide supported schizophrenia-associated genes: regulation by REST/NRSF, network organization and primate-specific evolution

The SMARCA2 gene, which encodes BRM in the SWI/SNF chromatin-remodeling complex, was recently identified as being associated with schizophrenia (SZ) in a genome-wide approach. Polymorphisms in SMARCA2, associated with the disease, produce changes in the expression of the gene and/or in the encoded amino acid sequence. We show here that an SWI/SNF-centered network including the Smarca2 gene is modified by the down-regulation of REST/NRSF in a mouse neuronal cell line. REST/NRSF down-regulation also modifies the levels of Smarce1, Smarcd3 and SWI/SNF interactors (Hdac1, RcoR1 and Mecp2). Smarca2 down-regulation generates an abnormal dendritic spine morphology that is an intermediate phenotype of SZ. We further found that 8 (CSF2RA, HIST1H2BJ, NOTCH4, NRGN, SHOX, SMARCA2, TCF4 and ZNF804A) out of 10 genome-wide supported SZ-associated genes are part of an interacting network (including SMARCA2), 5 members of which encode transcription regulators. The expression of 3 (TCF4, SMARCA2 and CSF2RA) of the 10 genome-wide supported SZ-associated genes is modified when the REST/NRSF-SWI/SNF chromatin-remodeling complex is experimentally manipulated in mouse cell lines and in transgenic mouse models. The REST/NRSF-SWI/SNF deregulation also results in the differential expression of genes that are clustered in chromosomes suggesting the induction of genome-wide epigenetic changes. Finally, we found that SMARCA2 interactors and the genome-wide supported SZ-associated genes are considerably enriched in genes displaying positive selection in primates and in the human lineage which suggests the occurrence of novel protein interactions in primates. Altogether, these data identify the SWI/SNF chromatin-remodeling complex as a key component of the genetic architecture of SZ.

DYRK1A interacts with the REST/NRSF-SWI/SNF chromatin remodelling complex to deregulate gene clusters involved in the neuronal phenotypic traits of Down syndrome

The molecular mechanisms that lead to the cognitive defects characteristic of Down syndrome (DS), the most frequent cause of mental retardation, have remained elusive. Here we use a transgenic DS mouse model (152F7 line) to show that DYRK1A gene dosage imbalance deregulates chromosomal clusters of genes located near neuron-restrictive silencer factor (REST/NRSF) binding sites. We found that Dyrk1a binds the SWI/SNF complex known to interact with REST/NRSF. The mutation of a REST/NRSF binding site in the promoter of the REST/NRSF target gene L1cam modifies the transcriptional effect of Dyrk1a-dosage imbalance on L1cam. Dyrk1a dosage imbalance perturbs Rest/Nrsf levels with decreased Rest/Nrsf expression in embryonic neurons and increased expression in adult neurons. Using transcriptome analysis of embryonic brain subregions of transgenic 152F7 mouse line, we identified a coordinated deregulation of multiple genes that are responsible for dendritic growth impairment present in DS. Similarly, Dyrk1a overexpression in primary mouse cortical neurons induced severe reduction of the dendritic growth and dendritic complexity. We propose that DYRK1A overexpression-related neuronal gene deregulation via disturbance of REST/NRSF levels, and the REST/NRSF-SWI/SNF chromatin remodelling complex, significantly contributes to the neural phenotypic changes that characterize DS.

Convergent evidence identifying MAP/microtubule affinity-regulating kinase 1 (MARK1) as a susceptibility gene for autism

Autism spectrum disorders (ASDs) are common, heritable, but genetically heterogeneous neurodevelopmental conditions. We recently defined a susceptibility locus for ASDs on chromosome 1q41-q42. High-resolution single-nucleotide polymorphisms (126 SNPs) genotyping across the chromosome 1q41-q42 region, followed by a MARK1 (microtubule affinity-regulating kinase 1)-tagged-SNP association study in 276 families with autism from the Autism Genetic Research Exchange, showed that several SNPs within the MARK1 gene were significantly associated with ASDs by transmission disequilibrium tests. Haplotype rs12740310*C-rs3737296*G-rs12410279*A was overtransmitted (P(corrected)= 0.0016), with a relative risk for autism of 1.8 in homozygous carriers. Furthermore, ASD-associated SNP rs12410279 modulates the level of transcription of MARK1. We found that MARK1 was overexpressed in the prefrontal cortex (BA46) but not in cerebellar granule cells, on postmortem brain tissues from patients. MARK1 displayed an accelerated evolution along the lineage leading to humans, suggesting possible involvement of this gene in cognition. MARK1 encodes a kinase-regulating microtubule-dependent transport in axons and dendrites. Both overexpression and silencing of MARK1 resulted in significantly shorter dendrite length in mouse neocortical neurons and modified dendritic transport speed. As expected for a gene encoding a key polarity determinant Par-1 protein kinase, MARK1 is involved in axon-dendrite specification. Thus, MARK1 overexpression in humans may be responsible for subtle changes in dendritic functioning.

The fragile X mental retardation protein is a molecular adaptor between the neurospecific KIF3C kinesin and dendritic RNA granules

Fragile X mental retardation 1 protein (FMRP) is an RNA-binding protein whose absence results in the fragile X syndrome, the most common inherited form of mental retardation. FMRP contains multiple domains with apparently differential affinity to mRNA and interacts also with protein partners present in ribonucleoprotein complexes called RNA granules. In neurons, these particles travel along dendrites and axons to translocate mRNAs to specific destinations in spines and growth cones, where local synthesis of neuro-specific proteins is taking place. However, the molecular mechanisms of how RNA granules are translocated to dendrites remained unknown. We report here the identification and characterization of the motor protein KIF3C as a novel FMRP-interacting protein. In addition, using time-lapse videomicroscopy, we studied the dynamics and kinetics of FMRP-containing RNA granules in dendrites and show that a KIF3C dominant-negative impedes their distal transport. We therefore propose that, in addition to modulate the translation of its mRNA targets, FMRP acts also as a molecular adaptor between RNA granules and the neurospecific kinesin KIF3C that powers their transport along neuronal microtubules.

Nrsf silencing induces molecular and subcellular changes linked to neuronal plasticity

Neurite outgrowth involves various molecular mechanisms generating complex brain connections. These mechanisms have been linked to plasticity and learning and are thought to be deregulated in neuropsychiatric diseases. The transcription factor REST/NRSF regulates a subset of genes encoding neurite outgrowth molecules. We demonstrate here the downregulation of Rest/Nrsf expression in a mouse neuroblastoma cell line. This downregulation induced a clear increase in neurite length. Quantitative polymerase chain reaction showed deregulation of the candidate genes L1cam, Elmo2, Ulip1 and Ulip2. These genes are bona fide candidates known to be involved in dendrite and axonal outgrowth. This approach could be adapted to high-throughput techniques for determination of the mammalian neurite outgrowth gene repertoire.

Ret deficiency in mice impairs the development of A5 and A6 neurons and the functional maturation of the respiratory rhythm

Although a normal respiratory rhythm is vital at birth, little is known about the genetic factors controlling the prenatal maturation of the respiratory network in mammals. In Phox2a mutant mice, which do not express A6 neurons, we previously hypothesized that the release of endogenous norepinephrine by A6 neurons is required for a normal respiratory rhythm to occur at birth. Here we investigated the role of the Ret gene, which encodes a transmembrane tyrosine kinase receptor, in the maturation of norepinephrine and respiratory systems. As Ret-null mutants (Ret-/-) did not survive after birth, our experiments were performed in wild-type (wt) and Ret-/- fetuses exteriorized from pregnant heterozygous mice at gestational day 18. First, in wt fetuses, quantitative in situ hybridization revealed high levels of Ret transcripts in the pontine A5 and A6 areas. Second, in Ret-/- fetuses, high-pressure liquid chromatography showed significantly reduced norepinephrine contents in the pons but not the medulla. Third, tyrosine hydroxylase immunocytochemistry revealed a significantly reduced number of pontine A5 and A6 neurons but not medullary norepinephrine neurons in Ret-/- fetuses. Finally, electrophysiological and pharmacological experiments performed on brainstem 'en bloc' preparations demonstrated impaired resting respiratory activity and abnormal responses to central hypoxia and norepinephrine application in Ret-/- fetuses. To conclude, our results show that Ret gene contributes to the prenatal maturation of A6 and A5 neurons and respiratory system. They support the hypothesis that the normal maturation of the respiratory network requires afferent activity corresponding to the A6 excitatory and A5 inhibitory input balance.

Molecular cloning and expression pattern of the Fkbp25 gene during cerebral cortical neurogenesis

Neocortical neurons are generated predominantly from the cells that proliferate in the ventricular zone of the telencephalon. In order to understand the nature of these expanding cortical neuronal progenitor cells, we selected by differential display some transcripts that were enriched in the telencephalon as compared to the more caudal regions (diencephalon/mesencephalon). This systematic screening revealed one of the differentially expressed transcripts, namely the Fkbp25 mRNA that encodes a member of the FK506 binding proteins (FKBPs). Northern blot analysis showed that the expression of the single 1.4kb Fkbp25 transcript reached a maximum level on embryonic day 11.5 at the start of cortical neurogenesis in the mouse and was followed by a weak basal expression in the adult brain. In the embryo, Fkbp25 gene was strongly expressed in the telencephalon ventricular zone but also in areas active in myogenesis (walls of the ventricle and the atrium) and chondrogenesis (the cartilage of the rib and the hindlimb). An increase in the transcript levels of the Fkbp25 gene was also observed during the two successive proliferation waves of the cerebellum development. Immunostaining on primary cultures of embryonic day 10.5 telencephalon stem cells showed that the Fkbp25 protein was present in the cytoplasm and nuclei of cells cultured for 6h but exclusively in the nuclei of the Tuj-1 immunoreactive neurons obtained after 3 days of culture (The sequence data reported here have been submitted to GenBank under accession no. AF135595.).

Expression pattern of NOGO and NgR genes during human development

Nogo protein has been identified as the component of central nervous system (CNS) myelin that limits axonal regeneration. We investigated the expression of the genes encoding Nogo and its receptor, NgR, between weeks eight and 23 of human embryonic development, by quantitative radioactive in situ hybridization. At 8 weeks, we detected NOGO and NgR transcripts in developing neuronal and non-neuronal structures. We focused on two different structures: the brain and the dental germs. During this period of development, NOGO and NgR transcripts colocalized in the cortical and ventricular zones of the brain, with expression strongest for these two genes in the postmitotic cells of the cortical plate. In developing dental germs, NgR was more strongly expressed than NOGO at 16 and 21 weeks. NOGO and NgR were expressed in zones of epithelium-mesenchyme interaction, which induce the differentiation of ameloblasts/odontoblasts. These genes were expressed most strongly in differentiated cells.

Modulation of the respiratory rhythm generator by the pontine noradrenergic A5 and A6 groups in rodents

The aim of the present review is to summarise available studies dealing with the respiratory control exerted by pontine noradrenergic neurones in neonatal and adult mammals. During the perinatal period, in vitro studies on neonatal rodents have shown that A5 and A6 neurones exert opposite modulations onto the respiratory rhythm generator, inhibitory and facilitatory respectively, that the anatomical support for these modulations already exists at birth, and that genetically induced alterations in the formation of A5 and A6 neurones affect the maturation of the respiratory rhythm generator, leading to lethal respiratory deficits at birth. The A5-A6 modulation of the respiratory rhythm generator is not transient, occurring solely during the perinatal period but it persists throughout life: A5 and A6 neurones display a respiratory-related activity, receive inputs from and send information to the medullary respiratory centres and contribute to the adaptation of adult breathing to physiological needs.

Identification of a novel brain-specific and reelin-regulated gene that encodes a protein colocalized with synapsin

We carried out a screening of genes that are differentially expressed in normal mice and reeler mutants and are characterized by abnormal neuronal migration and neurite deployment due to defective Reelin signalling. A novel gene, provisionally named C61, was overexpressed in Reelin-deficient embryonic mouse brain RNA. C61 encodes a 3.7 kb mRNA that is brain specific and developmentally regulated, with predominant expression in differentiating neurons. The predicted protein is 664 amino acids long, and contains LAG1 and Ezrin/Radixin/Moesin-Myosin-Filament motifs, suggesting that it may function as an intracellular adaptor. From E14.5 to birth, C61 was highly expressed in all neuronal differentiation fields, with the highest signal in the telencephalic cortical plate and mitral cells in the olfactory bulb. When expressed as a GFP fusion protein in transfected non-neuronal cells and primary neurons, this protein localizes, respectively, to the nuclear membrane or axonal outgrowths, indicating a function in axonal traffic or signalling.

Survival motor neuron SMN1 and SMN2 gene promoters: identical sequences and differential expression in neurons and non-neuronal cells

Spinal muscular atrophy (SMA) is a recessive disorder involving the loss of motor neurons from the spinal cord. Homozygous absence of the survival of motor neuron 1 gene (SMN1) is the main cause of SMA, but disease severity depends primarily on the number of SMN2 gene copies. SMN protein levels are high in normal spinal cord and much lower in the spinal cord of SMA patients, suggesting neuron-specific regulation for this ubiquitously expressed gene. We isolated genomic DNA from individuals with SMN1 or SMN2 deletions and sequenced 4.6 kb of the 5' upstream regions of the these. We found that these upstream regions, one of which is telomeric and the other centromeric, were identical. We investigated the early regulation of SMN expression by transiently transfecting mouse embryonic spinal cord and fibroblast primary cultures with three transgenes containing 1.8, 3.2 and 4.6, respectively, of the SMN promoter driving beta-galactosidase gene expression. The 4.6 kb construct gave reporter gene expression levels five times higher in neurons than in fibroblasts, due to the combined effects of a general enhancer and a non-neuronal cell silencer. The differential expression observed in neurons and fibroblasts suggests that the SMN genes play a neuron-specific role during development. An understanding of the mechanisms regulating SMN promoter activity may provide new avenues for the treatment of SMA.

Genetics and early disturbances of breathing control

Early disturbances in breathing control, including apneas of prematurity and apparently life-threatening events, account for some cases of sudden infant death syndrome and for a rare disorder called congenital central hypoventilation syndrome (CCHS). Data suggesting a genetic basis for CCHS have been obtained. Recently, we found heterozygous de novo mutations of the PHOX2B gene in 18 of 29 individuals with CCHS. Most mutations consisted of five to nine alanine expansions within a 20-residue polyalanine tract, probably resulting from nonhomologous recombination. Other mutations, generally inherited from one of the parents, in the coding regions of genes involved in the endothelin and RET signaling pathways and in the brain-derived-neurotrophic factor (BDNF) gene have been found in a few CCHS patients. Interestingly, all these genes are involved in the development of neural crest cells. Targeted disruption of these genes in mice has provided information on the pathophysiological mechanisms underlying CCHS. Despite the identification of these genes involved in breathing control, none of the genetically engineered mice developed to date replicate the full human CCHS respiratory phenotype. Recent insights into the genetic basis for CCHS may shed light on the genetics of other early disturbances in breathing control, such as apnea of prematurity and sudden infant death syndrome.

Expression of the RSK2 gene during early human development

The 90 kDa ribosomal S6 serine/threonine kinase 2 gene (RSK2, U08316) has been recently identified as a disease-causing gene in an X-linked disorder, the Coffin-Lowry Syndrome (MIM 303600) characterized by severe mental retardation, facial dysmorphisms and progressive skeletal malformations. To investigate its possible role in cerebral cortex development, we performed RNA in situ hybridization at three stages of human development: day 32 (Carnegie 15), 9 weeks (Carnegie 23) and 13 weeks. RSK2 expression is detected in the embryonic anterior and posterior telencephalon (hippocampus anlagen), mesencephalon, rhombencephalon and cerebellum. RSK2 gene expression is also observed in dorsal root ganglia, cranial nerve ganglia, and sensory epithelium of the inner ear, liver, lung and jaw anlagen. This pattern of expression may be involved in cognitive impairment and facial dysmorphisms found in Coffin-Lowry Syndrome.

Noradrenergic neuronal development is impaired by mutation of the proneural HASH-1 gene in congenital central hypoventilation syndrome (Ondine's curse)

Congenital central hypoventilation syndrome (CCHS, Ondine's curse) is a rare disorder of the chemical control of breathing. It is frequently associated with a broad spectrum of dysautonomic symptoms, suggesting the involvement of genes widely expressed in the autonomic nervous system. In particular, the HASH-1-PHOX2A-PHOX2B developmental cascade was proposed as a candidate pathway because it controls the development of neurons with a definitive or transient noradrenergic phenotype, upstream from the RET receptor tyrosine kinase and tyrosine hydroxylase. We recently showed that PHOX2B is the major CCHS locus, whose mutation accounts for 60% of cases. We also studied the proneural HASH-1 gene and identified a heterozygous nucleotide substitution in three CCHS patients. To analyze the functional consequences of HASH-1 mutations, we developed an in vitro model of noradrenergic differentiation in neuronal progenitors derived from the mouse vagal neural crest, reproducing in vitro the HASH-PHOX-RET pathway. All HASH-1 mutant alleles impaired noradrenergic neuronal development, when overexpressed from adenoviral constructs. Thus, HASH-1 mutations may contribute to the CCHS phenotype in rare cases, consistent with the view that the abnormal chemical control of breathing observed in CCHS patients is due to the impairment of noradrenergic neurons during early steps of brainstem development.

Genes modulating chemical breathing control: lessons from mutant animals

Genetic factors influence breathing control. Respiratory phenotypes of mutant mice may help to better understand these factors. Congenital central hypoventilation syndrome (CCHS) is a rare disorder defined as failure of chemical control of breathing causing central alveolar hypoventilation, especially during sleep. A genetic basis for CCHS is supported by several arguments, mainly the identification, in a few CCHS patients, of heterozygous mutations of genes contributing to neural crest cell development, namely, genes involved in the endothelin and c-ret pathways. Furthermore, plethysmography studies of the respiratory phenotypes of newborn heterozygous mutant mice have shown that genes in both pathways are involved in breathing control at birth. Nevertheless, no single gene mutation in newborn mice reproduces the human CCHS phenotype. Avenues for future research into the genetics of CCHS include (i) testing of mutant newborn mice for genes in other pathways and (ii) use of microarrays to identify gene clusters that should be associated with abnormal chemical breathing control.

Polyalanine expansion and frameshift mutations of the paired-like homeobox gene PHOX2B in congenital central hypoventilation syndrome

Congenital central hypoventilation syndrome (CCHS or Ondine's curse; OMIM 209880) is a life-threatening disorder involving an impaired ventilatory response to hypercarbia and hypoxemia. This core phenotype is associated with lower-penetrance anomalies of the autonomic nervous system (ANS) including Hirschsprung disease and tumors of neural-crest derivatives such as ganglioneuromas and neuroblastomas. In mice, the development of ANS reflex circuits is dependent on the paired-like homeobox gene Phox2b. Thus, we regarded its human ortholog, PHOX2B, as a candidate gene in CCHS. We found heterozygous de novo mutations in PHOX2B in 18 of 29 individuals with CCHS. Most mutations consisted of 5-9 alanine expansions within a 20-residue polyalanine tract probably resulting from non-homologous recombination. We show that PHOX2B is expressed in both the central and the peripheral ANS during human embryonic development. Our data support an essential role of PHOX2B in the normal patterning of the autonomous ventilation system and, more generally, of the ANS in humans.

Exclusion of RNX as a major gene in congenital central hypoventilation syndrome (CCHS, Ondine's curse)

Congenital central hypoventilation syndrome (CCHS) is a rare condition for which segregation analyses have suggested genetic factors. The respiratory phenotype of Rnx knock-out mice together with the Rnx expression at the brainstem level prompted us to consider the RNX gene as a candidate for CCHS in human. The screening of the RNX gene in a series of 25 patients with CCHS did not reveal any significant nucleotide variation. We therefore conclude that RNX is not a major gene for CCHS in human.

[Genetics and respiratory control: studies in normal humans and genetically modified animals]

INTRODUCTION

Studies into the contribution of genetic factors to respiratory control disorders are scarce, with impediments to their conduct including difficulties in characterizing these disorders, the large number of genes involved in respiratory control, and interactions between genetic and environmental factors.

STATE OF THE ART

The rare congenital central hypoventilation syndrome (CCHS) has opened up the field of respiratory control genetics. Heterozygous mutations of genes involved in neural crest development were discovered recently. Studies in mutant mice have identified respiratory control disturbances related to loss of function of genes involved in neural crest development, genes encoding transcription factors, diffusible factors, and proteins contributing to neurotransmission.

PERSPECTIVES

Future genetic epidemiological studies in humans and new models of mutant mice should describe genes involved in respiratory control. Better knowledge of CCHS genetics should provide guideposts for investigating the genetics of other respiratory control disorders.

CONCLUSIONS

Respiratory control genetics is opening up new paths for research into respiratory physiology and pathophysiology.

Glial cell line derived neurotrophic factor is expressed by epithelia of human renal dysplasia

PURPOSE

Differentiation of the metanephros is abnormal in cases of renal dysplasia, resulting in abnormal kidney organization. In vitro and in vivo studies indicate that glial cell line derived neurotrophic factor (GDNF) is a major regulator of kidney development and ureteral arborization. Therefore, we investigated the pattern of GDNF gene expression in human dysplastic kidneys.

MATERIALS AND METHODS

Specimens of whole tissues of human normal and dysplastic kidneys associated with obstructive uropathy were analyzed for GDNF mRNA by reverse transcriptase-polymerase chain reaction (RT-PCR). Immunohistochemistry with GDNF antibody and laser capture microdissection plus RT-PCR were done to identify cells producing GDNF. Apoptosis, BCL-2 and Ki67 were also studied.

RESULTS

There were few if any GDNF transcripts in normal kidneys, whereas GDNF was over expressed in renal dysplasia specimens. Strong GDNF expression was found in the dysplastic tubules of dysplastic kidneys, whereas peritubular mesenchyma expressed no GDNF protein. Laser capture microdissection/RT-PCR detected GDNF mRNA in epithelial cells isolated from dysplastic tubules but not in cells from the surrounding mesenchyma, which was confirmed by sequence analysis. GDNF expression by epithelial cells was associated with high proliferation, BCL-2 expression and rare apoptosis.

CONCLUSIONS

GDNF gene expression is restricted to the tubular epithelium of dysplastic human kidneys. Our results strongly suggest that GDNF not only influences kidney morphogenesis, but is also implicated in abnormal kidney development.

Glial cell line derived neurotrophic factor is expressed by epithelia of human renal dysplasia

PURPOSE

Differentiation of the metanephros is abnormal in cases of renal dysplasia, resulting in abnormal kidney organization. In vitro and in vivo studies indicate that glial cell line derived neurotrophic factor (GDNF) is a major regulator of kidney development and ureteral arborization. Therefore, we investigated the pattern of GDNF gene expression in human dysplastic kidneys.

MATERIALS AND METHODS

Specimens of whole tissues of human normal and dysplastic kidneys associated with obstructive uropathy were analyzed for GDNF mRNA by reverse transcriptase-polymerase chain reaction (RT-PCR). Immunohistochemistry with GDNF antibody and laser capture microdissection plus RT-PCR were done to identify cells producing GDNF. Apoptosis, BCL-2 and Ki67 were also studied.

RESULTS

There were few if any GDNF transcripts in normal kidneys, whereas GDNF was over expressed in renal dysplasia specimens. Strong GDNF expression was found in the dysplastic tubules of dysplastic kidneys, whereas peritubular mesenchyma expressed no GDNF protein. Laser capture microdissection/RT-PCR detected GDNF mRNA in epithelial cells isolated from dysplastic tubules but not in cells from the surrounding mesenchyma, which was confirmed by sequence analysis. GDNF expression by epithelial cells was associated with high proliferation, BCL-2 expression and rare apoptosis.

CONCLUSIONS

GDNF gene expression is restricted to the tubular epithelium of dysplastic human kidneys. Our results strongly suggest that GDNF not only influences kidney morphogenesis, but is also implicated in abnormal kidney development.

Perinatal nicotine attenuates the hypoxia-induced up-regulation of tyrosine hydroxylase and galanin mRNA in locus ceruleus of the newborn mouse

The effect of perinatal nicotine exposure on the hypoxic response in the newborn mouse was examined, with special reference to the catecholaminergic system. We studied transcripts for the catecholamine synthesizing enzyme tyrosine hydroxylase (TH) and the neuropeptide galanin (GAL) in locus ceruleus (LC) and adrenal medulla at different times after birth and postnatal hypoxia. We thereafter investigated how perinatal nicotine affected these mRNA levels, as well as the ability of the newborn to survive severe hypoxia. TH mRNA levels increased postnatally in both LC and adrenals, reaching peak values at 24 h postnatally and thereafter stabilizing at lower levels. GAL mRNA also increased in the LC but did not decrease after 24 h. Acute hypoxia (5% O(2) for 60 min) elicited increases in TH and GAL mRNA levels in the LC after 24 h. However, TH mRNA levels in the adrenals did not change. Perinatal nicotine exposure increased mortality after hypoxia (from 0% to 16.9%). Moreover, hypoxia-induced increases in TH and GAL mRNA levels in the LC were not observed in nicotine-treated pups. Nicotine also decreased basal TH mRNA levels in the adrenals. The present results suggest (1) that the postnatal increases in adrenal TH mRNA levels are not directly due to hypoxia at birth, and (2) that the increased mortality seen after hypoxia in nicotine pups concurs with a perturbed LC function in these animals. A deficient catecholamine synthesis in the adrenals may also contribute to the detrimental effect of prenatal exposure to nicotine on the response to hypoxia.

Ventilatory responses to hypercapnia and hypoxia in heterozygous c-ret newborn mice

The c-ret proto-oncogene encodes a tyrosine-kinase receptor involved in survival and differentiation of neural crest cell lineages. Previous studies have shown that homozygous c-ret-/- mice die soon after birth and have impaired ventilatory responses to hypercapnia. Heterozygous c-ret +/- mice develop normally, but their respiratory phenotype has not been described in detail. We used whole-body flow plethysmography to compare baseline breathing and ventilatory and arousal responses to chemical stimuli in unrestrained heterozygous c-ret +/- newborn mice and their wild-type c-ret +/+ littermates at 10-12 h of postnatal age. The hyperpnoeic and arousal responses to hypoxia and hypercapnia were not significantly different in these two groups. However, the number and total duration of apnoeas and periodic breathing episodes were significantly higher in c-ret +/- than in c-ret +/+ pups during hypoxia and post-hypoxic normoxia. These results are further evidence that respiratory control at birth is heavily dependent on genes involved in the neural determination of neural crest cells.

Murine peripherin gene sequences direct Cre recombinase expression to peripheral neurons in transgenic mice

Spatially and temporally regulated somatic mutations can be achieved by using the Cre/loxP recombination system of bacteriophage P1. To develop a cell type-specific system of gene targeting in the peripheral nervous system, we generated the transgenic mouse lines expressing Cre recombinase under the control of the mouse peripherin gene promoter. The activity of the Cre recombinase during embryonic development was examined by mating the peripherin-Cre transgenic mice to the knock-in Cre-mediated recombination reporter strain, R26R. Analysis of F1 embryos from this cross showed specific excision of loxP-flanked sequences in the dorsal root ganglia, trigeminal ganglia, and olfactory epithelium, in a pattern very similar to the expression of the endogenous mouse peripherin gene, and the previously reported peripherin-lacZ transgenic mice. Thus, the peripherin-Cre mouse described here will provide a valuable tool for Cre-loxP-mediated conditional expression in the peripheral nervous system.

Early neuronal and glial determination from mouse E10.5 telencephalon embryonic stem cells: an in vitro study

We report here a novel in vitro model for differentiating neuronal and glial cells from mouse embryonic day 10 telencephalon stem cells. At this developmental stage, the telencephalon consists of a single layer of neuroepithelial stem cells. We used various markers of proliferation and differentiation (Ki-67, nestin, BrdU, Tuj-1 and GFAP) to follow proliferative progenitors and to identify neuronal and glial derivatives. Neuronal derivatives were obtained from nestin+ progenitors. GFAP+ astrocytic derivatives were detected after only 72 h of culture. Both neuronal and glial derivatives were generated close to nestin-positive aggregates. In addition, we were able to manipulate neuronal determination of telencephalon stem cells by gene transient transfection as demonstrated by RP42 gene overexpression. These observations suggest that this in vitro model is of potential use for studying early steps in neuronal or glial determination from embryonic stem cells, an issue of key importance for adult brain cell therapy approaches.

[Evaluation of an information document about patients and transfusion]

OBJECTIVE

To evaluate the understanding of written information contained in the information sheet for patients intended to receive an homologous transfusion and to know their opinion about this document.

TYPE OF THE STUDY

A prospective cohort survey carried out by people unrelated to clinical units and transfusion services.

METHODS

A document divided in two parts, the first one summarized, the second detailed, was distributed to transfused adult patients. The patients were hospitalized in the general surgery and orthopedic wards of two hospitals and in the hematology and oncology wards of two different hospitals. A questionnaire was filled out in the presence of the inquirer.

RESULTS

Sixty one subjects have been enrolled, among them 53 considered the information as adequate; 53 as comforting and neutral. 53 patients considered a written information as essential and 52 estimated that both part of the information sheet (summarized and detailed) were mandatory. Conversely, a more in depth investigation revealed there was a gap between patients statements and their true understanding.

CONCLUSION

The value of a written information for the patients is confirmed by the study. In addition, patients were not generally worried by this information. The partition of the document has been appreciated. It is noteworthy that a gap exist between the patient's perception of the information and their actual level of understanding.

MASH-1/RET pathway involvement in development of brain stem control of respiratory frequency in newborn mice

Respiratory abnormalities have been described in MASH-1 (mammalian achaete-scute homologous gene) and c-RET ("rearranged during transfection") mutant newborn mice. However, the neural mechanisms underlying these abnormalities have not been studied. We tested the hypothesis that the MASH-1 mutation may impair c-RET expression in brain stem neurons involved in the control of breathing. To do this, we analyzed brain stem c-RET expression and respiratory phenotype in MASH-1 +/+ wild-type, MASH-1 +/- heterozygous, and MASH-1 -/- knock-out newborn mice during the first 2 h of life. In MASH-1 -/- newborns, c-RET gene expression was absent in the noradrenergic nuclei (A2, A5, A6, A7) that contribute to modulate respiratory frequency and in scattered cells of the rostral ventrolateral medulla. The c-RET transcript levels measured by quantitative RT-PCR were lower in MASH-1 -/- and MASH-1 +/- than in MASH-1 +/+ brain stems (P = 0.001 and P = 0.003, respectively). Breath durations were shorter in MASH-1 -/- and MASH-1 +/- than in MASH-1 +/+ mice (P = 0.022) and were weakly correlated with c-RET transcript levels (P = 0.032). Taken together, these results provide evidence that MASH-1 is upstream of c-RET in noradrenergic brain stem neurons important for respiratory rhythm modulation.

Heart transplantation changes the expression of distinct gene families

We took advantage of the combination of a rat heart transplantation model with a modified differential display RT-PCR method to identify transcriptome changes in the right atria from transplanted compared with native hearts. Based on sequence homology search, the 37 cDNAs differentially displayed both 2 and 7 days posttransplantation were categorized into 7 unknown transcripts, 16 expressed sequence tags (ESTs), and 14 partially or completely characterized genes. The last group cDNAs, validated by relative RT-PCR, belonged to diverse gene families involved in specific metabolisms, protein synthesis, cell signaling, and transcription. Furthermore, we identified differential transcripts corresponding to denervation and fetal gene reexpression. We found coordinate downregulation of genes involved in energy metabolism and protein synthesis regulation, similar to that reported for senescent skeletal muscle. From these transcriptome changes, we propose that heart transplants and senescent muscles share common molecular mechanisms.

Identification and isolation of a full-length clone of mouse GMFB (Gmfb), a putative intracellular kinase regulator, differentially expressed in telencephalon

We identified new transcribed sequences, using a differential display paradigm to select genes expressed in proliferating neuroblasts from mouse telencephalon at 10 days of embryonic development. In this systematic search, we isolated a 361-bp partial 3' untranslated region (3' UTR) homologous to the 3' UTR of the human gene encoding a putative intracellular kinase regulator, glia maturation factor beta (GMFB). We cloned a full-length, 4,311-bp mouse cDNA containing a 270-bp 5' UTR, a 3,615-bp 3' UTR, and an open reading frame of 426 nucleotides encoding a putative 142 amino-acid protein, identical to human GMFB, with the exception of two amino acids. This 4.3-kb transcript is present in a variety of adult tissues and is developmentally regulated as shown by Northern blot analysis. Differential expression in telencephalon was demonstrated by quantification of radioactive relative RT-PCR and confirmed by in situ hybridization. The isolation of this full-length clone of mouse Gmfb should facilitate investigation of the intracellular mechanisms involved in the development of telencephalon.

GDNF expression in Wilms tumor

PURPOSE

Wilms tumor or nephroblastoma is a developmental tumor of the kidney and one of the most frequent solid tumors in childhood. It derives from metanephrotic blastema and mimics nephrogenesis in a disorganized manner, offering an adequate model for study of human nephrogenesis. GDNF (glial cell line derived neurotrophic factor), a potent proliferation and survival factor of dopaminergic neurons, has recently been shown to have an early and major role in nephrogenesis. We studied the expression of GDNF in Wilms tumor.

MATERIALS AND METHODS

The study included 20 patients with nephroblastoma whose age at surgery ranged from 2 months to 13 years. Expression of GDNF protein was analyzed by an immunohistochemical technique using anti-GDNF antibody. Presence of GDNF-messenger (m)RNA and receptors GFRalpha1 and GFRalpha2-mRNA was analyzed by reverse transcription polymerase chain reaction. Specimens were also studied to evaluate apoptosis, proliferation index and Bcl-2 expression.

RESULTS

GDNF expression was mainly found in the epithelial cells of the most differentiated tubes, GDNF and co-receptors mRNA were found in specimens and proliferative activity was found on the same tubes as GDNF expression. Bcl-2 was expressed strongly in epithelial cells, in an intermediate fashion in the blastema and faintly in mesenchyma. Apoptosis was of low frequency in structures strongly expressing GDNF.

CONCLUSIONS

We have shown that GDNF is expressed by nephroblastoma tissue of human kidneys. This expression is mainly in the differentiated epithelial component of the nephroblastoma. We have also shown that tissue strongly expressing GDNF is positively proliferative and has less apoptotic activity. We speculate that the role of GDNF may not be limited to normal nephrogenesis but may interact with other factors in the process of proliferation and apoptosis involved in nephroblastoma tumorigenesis.

Impaired ventilatory responses to hypoxia in mice deficient in endothelin-converting-enzyme-1

Endothelin-converting-enzyme (ECE-1) catalyzes the proteolytic activation of big endothelin-1 to mature endothelin-1. Most homozygous ECE-1-/- embryos die in utero and show severe craniofacial, enteric, and cardiac malformations precluding ventilatory function assessment. In contrast, heterozygous ECE-1+/- embryos develop normally. Their respiratory function at birth has not been studied. Taking into account previous respiratory investigations in mice with endothelin-1 gene disruption, we hypothesized that ECE-1-deficient mice may have impaired ventilatory control. We analyzed ventilatory responses to hypercapnia (8% CO(2)) and hypoxia (10% O(2)) in newborn and adult mice heterozygous for ECE-1 deficiency (ECE-1+/-) and in their wild-type littermates (ECE-1+/+). Ventilation, breath duration, and tidal volume were measured using whole-body plethysmography. Ventilatory responses to hypoxia were significantly weaker in ECE-1+/- than in ECE-1+/+ newborn mice (percentage ventilation increase: 1 +/- 25% versus 33 +/- 29%, p = 0.010). Baseline breathing variables and ventilatory responses to hypercapnia were normal in the ECE-1+/- newborn mice. No differences were observed between adult ECE-1+/- and ECE-1+/+ mice. We conclude that ECE-1 is required for normal ventilatory response to hypoxia at birth.

Caffeine-induced telencephalic vesicle evagination in early post-implantation mouse embryos involves cAMP-dependent protein kinase (PKA) inhibition

Other studies have shown that caffeine accelerates telencephalic vesicle evagination in early post-implantation mouse embryos. The present study examines the effect of caffeine on gene modulation in post-implantation mouse embryos. Using mRNA differential display, we observed that caffeine increased gene expression of the regulatory subunit (RI alpha) of cAMP-dependent protein kinase (PKA). RT--PCR analysis confirmed an increase in expression of this gene in caffeine-exposed embryos when compared with saline-treated controls. Using a fluorescent substrate of PKA, we found that PKA activity in the presence of cAMP was lower in caffeine-treated embryos than in controls. Treatment with H89 and PKI(12-24)amide, two inhibitors of PKA activity, mimicked the effects of caffeine on telencephalic vesicle formation. Together these data suggest that in early post-implantation mouse embryos caffeine modulates gene expression of the RI alpha subunit of PKA and that caffeine-induced inhibition of PKA activity plays a role in early telencephalic evagination.

Cloning and expression analysis of a novel gene, RP42, mapping to an autism susceptibility locus on 6q16

We isolated a novel mouse gene, RP42, in a systematic search for genes expressed in proliferating neuroblasts whose human orthologs map to susceptibility loci for autism. This gene is intronless and encodes a putative 259-amino-acid protein that exhibits 30-36% overall sequence identity to a fission yeast and a nematode protein (GenPept Accession Nos. CAA17006 and CAB54261). Nevertheless, no homology to any known gene was found. RP42 has developmentally regulated expression, particularly in proliferating neuroblasts from which neocortical neurons originate. Its human ortholog is located in a cluster of embryonic neuronally expressed genes on the 6q16 chromosome, making it a positional candidate susceptibility gene for autism.