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N Heintz

Publications and source records attributed to N Heintz.

At least 19 recordsLinked to original sources
PubMed2004

Increased motor drive and sleep loss in mice lacking Kv3-type potassium channels.

The voltage-gated potassium channels Kv3.1 and Kv3.3 are widely expressed in the brain, including areas implicated in the control of motor activity and in areas thought to regulate arousal states. Although Kv3.1 and Kv3.3-single mutants show some physiological changes, previous studies revealed relatively subtle behavioral alterations suggesting that Kv3.1 and Kv3.3 channel subunits may be encoded by a pair of redundant genes. In agreement with this hypothesis, Kv3.1/Kv3.3-deficient mice display a 'strong' mutant phenotype that includes motor dysfunction (ataxia, myoclonus, tremor) and hyperactivity when exposed to a novel environment. In this paper we report that Kv3.1/Kv3.3-deficient mice are also constitutively hyperactive. Compared to wildtype mice, double mutants display 'restlessness' that is particularly prominent during the light period, when mice are normally at rest, characterized by more than a doubling of ambulatory and stereotypic activity, and accompanied by a 40% sleep reduction. When we reinvestigated both single mutants, we observed constitutive increases of ambulatory and stereotypic activity in conjunction with sleep loss in Kv3.1-single mutants but not in Kv3.3-single mutants. These findings indicate that the absence of Kv3.1-channel subunits is primarily responsible for the increased motor drive and the reduction in sleep time.

Animals↗
PubMed2001

A rapid method for targeted modification and screening of recombinant bacterial artificial chromosome.

Modification of bacterial artificial chromosomes (BACs) has been a useful method to produce genomic DNA fragments for studying gene expression and function in vitro and in vivo. The original technique involved restrictions for BAC modification and required multiple cloning steps to target sequences into the shuttle vector. Selection and screening of BAC recombinants was accomplished by drug resistance and Southern blotting. We have developed a PCR-based method for producing the modified shuttle vectors and for screening for BACs carrying homologous integrants. The combination of these techniques allows for rapid and easy targeted BAC sequence deletion or insertion.

Base Sequence↗
PubMed2001

Alcohol hypersensitivity, increased locomotion, and spontaneous myoclonus in mice lacking the potassium channels Kv3.1 and Kv3.3.

The Shaw-like potassium (K(+)) channels Kv3.1 and Kv3.3 are widely coexpressed in distinct neuronal populations in the CNS, possibly explaining the relatively "mild" phenotypes of the Kv3.1 and the Kv3.3 single mutant. Kv3.1-deficient mice show increased cortical gamma- and decreased delta-oscillations (Joho et al., 1997, 1999); otherwise, the Kv3.1-mutant phenotype is relatively subtle (Ho et al., 1997; Sánchez et al., 2000). Kv3.3-deficient mice display no overt phenotype (Chan, 1997). To investigate whether Kv3.1 and Kv3.3 K(+) channels are functionally redundant, we generated the Kv3.1/Kv3.3 double mutant. Kv3.1/Kv3.3-deficient mice were born at the expected Mendelian frequencies indicating that neither Kv3.1 nor Kv3.3 K(+) channels are essential for embryonic development. Although there are no obvious changes in gross brain anatomy, adult Kv3.1/Kv3.3-deficient mice display severe ataxia, tremulous movements, myoclonus, and hypersensitivity to ethanol. Mice appear unbalanced when moving, whereas at rest they exhibit whole-body jerks every few seconds. In spite of the severe motor impairment, Kv3.1/Kv3.3-deficient mice are hyperactive, show increased exploratory activity, and display no obvious learning or memory deficit. Myoclonus, tremor, and ethanol hypersensitivity are only seen in the double-homozygous Kv3.1/Kv3.3-deficient mice, whereas increased locomotor and exploratory activity are also present in double-heterozygous mice. The graded penetrance of mutant traits appears to depend on the number of null alleles, suggesting that some of the distinct phenotypic traits visible in the absence of Kv3.1 and Kv3.3 K(+) channels are unrelated and may be caused by localized dysfunction in different brain regions.

Animals↗
PubMed2000

The Lurcher mutation identifies delta 2 as an AMPA/kainate receptor-like channel that is potentiated by Ca(2+).

Neurodegeneration in Lurcher (Lc) mice results from constitutive activation of delta 2, a subunit of ionotropic glutamate receptors (GluRs) with unknown natural ligands and channel properties. Homo-oligomeric channels of GluR-delta2 with the Lurcher mutation (GluR-delta 2(Lc)) expressed in human embryonic kidney 293 cells showed a doubly rectifying current-voltage relation reminiscent of the block by intracellular polyamines in AMPA/kainate channels. Similarly, the fraction of the total current carried by Ca(2+) was approximately 2-3%, comparable with that found in Ca(2+)-permeable AMPA/kainate channels. Currents through GluR-delta 2(Lc) channels were also potentiated by extracellular Ca(2+) in a biphasic manner, with maximal potentiation occurring at physiological concentrations of Ca(2+). We examined the functional role of the Q/R site in GluR-delta 2(Lc) by replacing glutamine with arginine. Analogous to AMPA/kainate receptors, GluR-delta 2(Lc)(R) channels showed no voltage-dependent block by intracellular polyamines and were nominally impermeable to Ca(2+). The potentiation by Ca(2+), however, remained intact. Hence, GluR-delta 2(Lc) channels are functionally similar to the AMPA/kainate receptor channels, consistent with the high-sequence identity shared by these subunits within the channel-lining M2 and M3 segments. Furthermore, potentiation by Ca(2+) and a permeability to Ca(2+) comparable with that of AMPA/kainate receptors provide a possible cause for cell death in Lurcher mice and may contribute to cerebellar long-term depression under physiological conditions.

Animals↗
PubMed2000

Neurodegeneration in Lurcher mice occurs via multiple cell death pathways.

Lurcher (Lc) is a gain-of-function mutation in the delta2 glutamate receptor (GRID2) that results in the cell-autonomous death of cerebellar Purkinje cells in heterozygous lurcher (+/Lc) mice. This in turn triggers the massive loss of afferent granule cells during the first few postnatal weeks. Evidence suggests that the death of Purkinje cells as a direct consequence of GRID2(Lc) activation and the secondary death of granule cells because of target deprivation occur by apoptosis. We have used mice carrying null mutations of both the Bax and p53 genes to examine the roles of these genes in cell loss in lurcher animals. The absence of Bax delayed Purkinje cell death in response to the GRID2(Lc) mutation and permanently rescued the secondary death of granule cells. In contrast, the p53 deletion had no effect on either cell death pathway. Our results demonstrate that target deprivation induces a Bax-dependent, p53-independent cell death response in cerebellar granule cells in vivo. In contrast, Bax plays a minor role in GRID2(Lc)-mediated Purkinje cell death.

Animals↗
PubMed2000

Analysis of mammalian central nervous system gene expression and function using bacterial artificial chromosome-mediated transgenesis.

The anatomical complexity of the mammalian central nervous system (CNS) presents special problems for the analysis of CNS gene expression and function. The most difficult challenge is presented by the simple fact that there are hundreds of functionally and morphologically defined cell types in the CNS. Given this complexity, the interpretation of CNS phenotypes is often problematic. The preparation of transgenic mice carrying marked bacterial artificial chromosomes (BACs) provides an important avenue for improving our understanding of CNS-expressed genes and phenotypes. This approach can allow efficient analysis of patterns of gene expression, subcellular localization of their encoded products and neuronal projection patterns. BAC transgenic mice can also provide access to information relevant to gene function based on phenotypes arising from increased gene dosage or expression of activating and dominant-negative alleles. This review will concentrate on these issues and their relevance to the analysis of CNS-expressed genes.

Animals↗
PubMed2000

Insights from mouse models into the molecular basis of neurodegeneration.

Thanks largely to cloning the genes for several neurodegenerative diseases over the past decade and the existence of mouse mutants, the molecular basis of neurodegeneration is finally beginning to yield some of its secrets. We discuss what has been learned about the pathogenesis of "triplet repeat" diseases through mouse models for spinocerebellar ataxia types 1 and 3 and Huntington disease, including the roles of nuclear aggregates and protein cleavage. We also discuss the neurologic phenotypes that arise from mutations in neurotransmitter receptors (lurcher mice) and ion channels (weaver, leaner, and tottering mice), drawing parallels between ischemic cell death and the neurodegeneration that occurs in the lurcher mouse. Finally, we discuss common mechanisms of cell death and lessons learned from these mouse models that might have broader relevance to other neurologic disorders.

Animals↗
PubMed1999

GluR delta 2 and the development and death of cerebellar Purkinje neurons in lurcher mice.

Lurcher (Lc) is a spontaneous, semidominant mouse neurological mutation. Heterozygous lurcher mice (Lc/+) display ataxia due to a selective, cell-autonomous, apoptotic death of 90% of cerebellar Purkinje cells during postnatal development. Homozygous lurcher mice (Lc/Lc) die shortly after birth due to massive loss of mid- and hindbrain neurons during late embryogenesis. We identified the mutations responsible for neurodegeneration in two independent Lc alleles as identical G-to-A transitions that change a highly conserved alanine to a threonine residue in transmembrane domain III of the mouse delta 2 glutamate receptor gene (GluRE2). Lc/+ Purkinje cells displayed a very high membrane conductance and a depolarized resting potential, indicating the presence of a large, constitutive inward current. Expression of the mutant GluR delta 2Lc protein in Xenopus oocytes confirmed these results, demonstrating that lurcher is an inherited neurodegenerative disorder resulting from a gain-of-function mutation in a glutamate receptor gene. Further characterization of GluR delta 2 signaling and the activation of apoptotic death in Lc Purkinje cells have begun to yield mechanistic insights into this neurodegenerative disease, and to highlight its relationship to neuronal loss following ischemia.

Amino Acid Sequence↗
PubMed1999

lynx1, an endogenous toxin-like modulator of nicotinic acetylcholine receptors in the mammalian CNS.

Elapid snake venom neurotoxins exert their effects through high-affinity interactions with specific neurotransmitter receptors. A novel murine gene, lynx1, is highly expressed in the brain and contains the cysteine-rich motif characteristic of this class of neurotoxins. Primary sequence and gene structure analyses reveal an evolutionary relationship between lynx1 and the Ly-6/neurotoxin gene family. lynx1 is expressed in large projection neurons in the hippocampus, cortex, and cerebellum. In cerebellar neurons, lynx1 protein is localized to a specific subdomain including the soma and proximal dendrites. lynx1 binding to brain sections correlates with the distribution of nAChRs, and application of lynx1 to Xenopus oocytes expressing nAChRs results in an increase in acetylcholine-evoked macroscopic currents. These results identify lynx1 as a novel protein modulator for nAChRs in vitro, which could have important implications in the regulation of cholinergic function in vivo.

Adaptor Proteins, Signal Transducing↗
PubMed1999

BAC-mediated gene-dosage analysis reveals a role for Zipro1 (Ru49/Zfp38) in progenitor cell proliferation in cerebellum and skin.

Genetic analysis in mice has most commonly employed two general strategies: phenotypic screens for spontaneous or induced mutations and genotypic analysis using homologous recombination or gene trapping to produce deletion or insertion mutants. Here we use bacterial artificial chromosome (BAC)-mediated gene-dosage analysis in transgenic mice to reveal novel genetic functions that are not evident from conventional loss-of-function mutations. We demonstrate a role for the zinc-finger transcription factor Zipro1 (formerly Ru49 and Zfp38) in the proliferation of granule cell precursors in the developing cerebellum, and document the contribution of this process to the final stages of cerebellar morphogenesis. We also show that Zipro1 is expressed in skin, and increased Zipro1 dosage results in a hair-loss phenotype associated with increased epithelial cell proliferation and abnormal hair follicle development.

Animals↗
PubMed1998

A high-resolution genetic map of the nervous locus on mouse chromosome 8.

The nervous (nr) mutant mouse displays two gross recessive traits: both an exaggeration of juvenile hyperactivity and a pronounced ataxia become apparent during the third and fourth postnatal weeks. Using an intersubspecific intercross, we have established a high-resolution map of a segment of mouse chromosome 8 that places the nr locus in a genomic segment defined by D8Rck1 on the centromeric end and D8Mit3 on the telomeric end. This map position places the nr locus within the BALB/cGr congenic region of the C3HeB/ FeJ-nr strain, confirming the accuracy of our study. We used this map position to identify and evaluate three genes-ankyrin 1, cortexin, and farnesyltransferase-as candidates for the nr gene. These three genes were eliminated from consideration but allowed us to establish the conservation of synteny between the region containing the nr locus and a segment of the short arm of human chromosome 8 (8p21-p11.2). Finally, the incomplete penetrance of the nr phenotype led us to perform a screen for modifier loci, and we present evidence that such a nervous modifier locus may exist on mouse chromosome 5.

Adjuvants, Immunologic↗
PubMed1998

The human glutamate receptor delta 2 gene (GRID2) maps to chromosome 4q22.

We isolated the human glutamate receptor delta 2 (GRID2) gene, which has 97.0% identity in amino acid sequence to the mouse glutamate receptor delta 2 (Grid2) gene. We subsequently mapped this gene to human chromosome 4q22 by radiation hybrid mapping and by hybridization to two overlapping human yeast artificial chromosomes that are located in 4q22. The Grid2 gene, which is mutated in lurcher (Lc) mice, maps to mouse chromosome 6. Thus, the mapping of the GRID2 gene to human chromosome 4q22 confirms and refines a region of synteny between mouse and human genomes.

Amino Acid Sequence↗
PubMed1998

The lurcher mutation and ionotropic glutamate receptors: contributions to programmed neuronal death in vivo.

The recent positional cloning and physiological characterization of the lurcher mutation resulted in the identification of a novel stimulus that results in neurodegeneration. The catastrophic loss of cerebellar Purkinje cells in lurcher heterozygotes has now been strongly associated with a large constitutive inward current which ultimately activates a programmed form of neuronal death. The completely penetrant and focal nature of the lurcher phenotype gives us an opportunity to investigate the manner in which neurons respond to an aberrant signal in the context of the brain parenchyma. Although there is no human genetic disease that is equivalent to the lurcher mutation at this time, its triggering of programmed neuronal death enables us to pose and address questions that are relevant to a large number of human neurological diseases. The advantage of working in a genetically manipulable in vivo mammalian system is evident: we can address questions relating to gene function in the nervous system in a context that is physiological. Classical genetic analyses looking for molecules that suppress or modify the lurcher phenotype are under way and have now been supplemented with two novel techniques developed in our laboratory: biolistic transfection of cerebellar slices and Bacterial Artificial Chromosome modification. The integration of these novel and classical approaches will facilitate the testing of hypotheses, developed during the course of our study of the lurcher mutation, which explore the propagation of abnormal signals and the initiation of programmed neuronal death in neurons.

Amino Acid Sequence↗
PubMed1998

Changing patterns of gene expression identify multiple steps during regression of rat prostate in vivo.

The rat ventral prostate is an androgen-dependent organ that undergoes dramatic cell death upon removal of testosterone by surgical castration. Several well characterized criteria, such as nuclear condensation, organelle blebbing, and DNA fragmentation, have been used to demonstrate that most of this cell loss is due to programmed cell death, or apoptosis, of the secretory epithelial cells. In addition to changes in morphology, it is well known that cells undergoing apoptosis show alterations in gene expression, and it is widely assumed that many of these genes are directly involved in the mechanism of programmed cell death. Using poly A+ RNA derived from normal rat prostate as well as from the regressing prostates of castrated rats, we have used a PCR-based subtractive hybridization approach to generate complementary DNA (cDNA) libraries greatly enriched in cDNAs strongly regulated during rat prostate regression. Several hundred of the genes represented in these libraries appear to be strongly regulated during prostate regression and most of these are prostate specific. Sequence analysis indicates that up to 30% of these clones are similar or identical to genes of known function, approximately 20% are similar to expressed sequence tags (ESTs), and as many as 50% of these clones have not been characterized previously. Analysis of selected clones using in situ hybridization indicates that they are expressed specifically in prostate epithelial cells, and that certain of these clones are regulated temporally in a pattern consistent with apoptosis. The patterns of gene expression include: 1) genes whose expression decreases uniformly after removal of androgen, indicative of androgen sensitive genes; 2) genes whose expression increases in apoptotic prostate cells and in other tissues, suggesting a class of genes generally involved in apoptosis; 3) and genes whose expression increases in individual regressing prostate epithelial cells, suggesting a class of prostate specific genes associated with apoptosis.

Animals↗
PubMed1997

Expression of brain lipid binding protein in the brain of the adult canary and its implications for adult neurogenesis.

Brain lipid binding protein (BLBP), a member of the fatty acid binding protein family, is expressed at high levels in the mammalian central nervous system during development, but not in adulthood. Because the brain of adult birds continues to show significant levels of neurogenesis, we thought it likely that BLBP expression would also be present. We used a polyclonal antibody against BLBP to study the presence of this protein in the adult canary brain. This antibody stained 1) fibers and perikarya of radial cells in the telencephalon; 2) Bergmann glia in the cerebellum; 3) astrocytes; 4) tanicytes in the walls of the third ventricle; 5) the neuropil of certain forebrain and brainstem regions, including nuclei of the song system; and 6) some migrating cells in the telencephalon. This anatomical distribution suggests that BLBP plays a role in the neuronal migration and synaptic reorganization of adult avian brain.

Aging↗
PubMed1997

Neurodegeneration in Lurcher mice caused by mutation in delta2 glutamate receptor gene.

Lurcher (Lc) is a spontaneous, semidominant mouse neurological mutation. Heterozygous Lurcher mice (Lc/+) display ataxia as a result of a selective, cell-autonomous and apoptotic death of cerebellar Purkinje cells during postnatal development. Homozygous Lurcher mice (Lc/Lc) die shortly after birth because of a massive loss of mid- and hindbrain neurons during late embryogenesis. We have used positional cloning to identify the mutations responsible for neurodegeneration in two independent Lc alleles as G-to-A transitions that change a highly conserved alanine to a threonine residue in transmembrane domain III of the mouse delta2 glutamate receptor gene (GluR delta2). Lc/+ Purkinje cells have a very high membrane conductance and a depolarized resting potential, indicating the presence of a large, constitutive inward current. Expression of the mutant GluR delta2(Lc) protein in Xenopus oocytes confirmed these results, demonstrating that Lc is inherited as a neurodegenerative disorder resulting from a gain-of-function mutation in a glutamate receptor gene. Thus the activation of apoptotic neuronal death in Lurcher mice may provide a physiologically relevant model for excitotoxic cell death.

Amino Acid Sequence↗