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Albee Messing

Publications and source records attributed to Albee Messing.

31 records · Page 2Linked to original sources
PubMed2004

Expression specificity of GFAP transgenes.

Glial fibrillary acidic protein (GFAP) is an intermediate filament protein found predominantly in astrocytes. This specificity has recommended the GFAP gene promoter for targeting transgene expression to astrocytes. Although both we [Brenner et al. J. Neurosci. 14:1030-1037, (1994)] and others [Mucke et al. New Biol. 3:465-474, (1991)] have reported astrocyte specificity for GFAP promoters, we demonstrate here that these DNA sequences can also direct activity in neurons. The pattern of neuronal activity varied with both the nature of the expressed sequence and the transgene insertion site. Specifically, neuronal expression was very high for a protective protein/cathepsin A minigene, moderate for lacZ and undetectable for GFP. These findings, coupled with a survey of the literature, recommend that investigators using GFAP-driven transgenes verify specificity for each line studied, using a detection system whose sensitivity is sufficient to detect a compromising level of misexpression.

Adenosine Diphosphate↗
PubMed2004

Characterization of a Schwann cell enhancer in the myelin basic protein gene.

Oligodendrocytes and Schwann cells use diverse regulatory elements to transcribe myelin basic protein (Mbp). For example, an enhancer 9.0 kb upstream of Mbp (MbpSCE1) activated either the proximal Mbp or hsp68 promoters only in Schwann cells in transgenic mice. Here, we analyze MbpSCE1 in vitro and in vivo and show that MbpSCE1 also activates another myelin gene, Mpz, specifically in Schwann cells in transgenic mice. Surprisingly, although MbpSCE1 behaves as an enhancer in Schwann cells, we show here for the first time that it also activates transcription robustly in cultured oligodendrocytes, but only from its original genomic position. Diverse nuclear proteins binding at distinct combinations of DNA elements in the two cell types may account for cell-specific MbpSCE1 function. A further surprise is that MbpSCE1 activation does not depend on consensus binding sites for the myelin-associated PPARbeta or Krox 20 transcription factors. Finally, chromatin context augments activation of MbpSCE1. Therefore, MbpSCE1 is active in both Schwann cells and oligodendrocytes, but by diverse mechanisms.

Animals↗
PubMed2004

Severity of neurodegeneration correlates with compromise of iron metabolism in mice with iron regulatory protein deficiencies.

In mammals, iron regulatory proteins 1 and 2 (IRP1 and IRP2) posttranscriptionally regulate expression of several iron metabolism proteins including ferritin and transferrin receptor. Genetically engineered mice that lack IRP2, but have the normal complement of IRP1, develop adult-onset neurodegenerative disease associated with inappropriately high expression of ferritin in degenerating neurons. Here, we report that mice that are homozygous for a targeted deletion of IRP2 and heterozygous for a targeted deletion of IRP1 (IRP1+/- IRP2-/-) develop a much more severe form of neurodegeneration, characterized by widespread axonopathy and eventually by subtle vacuolization in several areas, particularly in the substantia nigra. Axonopathy develops in white matter tracts in which marked increases in ferric iron and ferritin expression are detected. Axonal degeneration is significant and widespread before evidence for abnormalities or loss of neuronal cell bodies can be detected. Ultimately, neuronal cell bodies degenerate in the substantia nigra and some other vulnerable areas, microglia are activated, and vacuoles appear. Mice manifest gait and motor impairment at stages when axonopathy is pronounced, but neuronal cell body loss is minimal. These observations suggest that therapeutic strategies that aim to revitalize neurons by treatment with neurotrophic factors may be of value in IRP2-/- and IRP1+/- IRP2-/- mouse models of neurodegeneration.

Age Factors↗
PubMed2003

Unique role of dystroglycan in peripheral nerve myelination, nodal structure, and sodium channel stabilization.

Dystroglycan is a central component of the dystrophin-glycoprotein complex implicated in the pathogenesis of several neuromuscular diseases. Although dystroglycan is expressed by Schwann cells, its normal peripheral nerve functions are unknown. Here we show that selective deletion of Schwann cell dystroglycan results in slowed nerve conduction and nodal changes including reduced sodium channel density and disorganized microvilli. Additional features of mutant mice include deficits in rotorod performance, aberrant pain responses, and abnormal myelin sheath folding. These data indicate that dystroglycan is crucial for both myelination and nodal architecture. Dystroglycan may be required for the normal maintenance of voltage-gated sodium channels at nodes of Ranvier, possibly by mediating trans interactions between Schwann cell microvilli and the nodal axolemma.

Animals↗
PubMed2003

Accelerated hippocampal spreading depression and enhanced locomotory activity in mice with astrocyte-directed inactivation of connexin43.

Using a human glial fibrillary acidic protein (hGFAP) promoter-driven cre transgene, we have achieved efficient inactivation of a floxed connexin43 (Cx43) gene in astrocytes of adult mice. The loss of Cx43 expression was monitored in a cell-autonomous manner via conditional replacement of the Cx43-coding region by a lacZ reporter gene. In this way, we bypassed the early postnatal lethality previously reported for Cx43 null mice and characterized the phenotypic consequences of Cx43 deficiency in the CNS. Mice lacking Cx43 in astrocytes were viable and showed no evidence of either neurodegeneration or astrogliosis. Spreading depression (SD) is a pathophysiological phenomenon observed in the CNS that is characterized by a propagating wave of depolarization followed by neuronal inactivation. Inhibitors of gap junctional communication have previously been shown to block initiation and propagation of SD. In contrast, we observed an increase in the velocity of hippocampal SD in the stratum radiatum of mice lacking Cx43 in astrocytes. In the same brain subregion, dye-coupling experiments revealed a reduction in overall astrocytic intercellular communication by approximately 50%. This strongly suggests separate and different neuronal and glial contributions of gap junctional intercellular communication to SD. Concomitant with increased velocity of spreading depression, we observed enhanced locomotory activity in mice lacking Cx43 in astrocytes.

Animals↗
PubMed2003

GFAP: functional implications gleaned from studies of genetically engineered mice.

GFAP is the major intermediate filament of mature astrocytes, and its relatively specific expression in these cells suggests an important function. To study the role of the GFAP gene, mice have been created carrying null alleles (no protein), modified alleles (altered protein), or added wild type alleles (elevated protein). Surprisingly, absence of GFAP has relatively subtle effects on development. On the other hand, over-expression can be lethal, and led to the discovery that GFAP coding mutations are responsible for most cases of Alexander disease, a devastating neurodegenerative disorder. Here we review what the various GFAP mouse models reveal about GFAP and astrocyte function.

Alexander Disease↗
PubMed2003

Experimental autoimmune encephalomyelitis relapses are reduced in heterozygous golli MBP knockout mice.

Increased golli MBP (golli) expression has been observed in the peripheral immune system of mice in the relapsing phase of EAE, raising the possibility that golli MBP expression in the periphery may contribute to relapses. Here we describe the generation of golli MBP-deficient mice and a comparison of the clinical course of EAE between heterozygous (golli(+/-)) and wild-type (golli(+/+)) mice. There was no difference between the two groups in incidence of disease, severity of the first episode of disease, or remission after the first episode. However, there was a significant reduction in relapses in golli(+/-) mice vs. controls, suggesting a role for golli proteins in the relapses in EAE.

Animals↗
PubMed2002

Deletion of brain dystroglycan recapitulates aspects of congenital muscular dystrophy.

Fukuyama congenital muscular dystrophy (FCMD), muscle-eye-brain disease (MEB), and Walker-Warburg syndrome are congenital muscular dystrophies (CMDs) with associated developmental brain defects. Mutations reported in genes of FCMD and MEB patients suggest that the genes may be involved in protein glycosylation. Dystroglycan is a highly glycosylated component of the muscle dystrophin-glycoprotein complex that is also expressed in brain, where its function is unknown. Here we show that brain-selective deletion of dystroglycan in mice is sufficient to cause CMD-like brain malformations, including disarray of cerebral cortical layering, fusion of cerebral hemispheres and cerebellar folia, and aberrant migration of granule cells. Dystroglycan-null brain loses its high-affinity binding to the extracellular matrix protein laminin, and shows discontinuities in the pial surface basal lamina (glia limitans) that probably underlie the neuronal migration errors. Furthermore, mutant mice have severely blunted hippocampal long-term potentiation with electrophysiologic characterization indicating that dystroglycan might have a postsynaptic role in learning and memory. Our data strongly support the hypothesis that defects in dystroglycan are central to the pathogenesis of structural and functional brain abnormalities seen in CMD.

Animals↗
PubMed2002

Genetic analysis of the mammalian K+ channel beta subunit Kvbeta 2 (Kcnab2).

Kvbeta2 binds to K(+) channel alpha subunits from at least two different families (Kv1 and Kv4) and is a member of the aldo-ketoreductase (AKR) superfamily. Proposed functions for this protein in vivo include a chaperone-like role in Kv1 alpha subunit biogenesis and catalytic activity as an AKR oxidoreductase. To investigate the in vivo function of Kvbeta2, Kvbeta2-null and point mutant (Y90F) mice were generated through gene targeting in embryonic stem cells. In Kvbeta2-null mice, Kv1.1 and Kv1.2 localize normally in cerebellar basket cell terminals and the juxtaparanodal region of myelinated nerves. Moreover, normal glycosylation patterns are observed for Kv1.1 and Kv1.2 in whole brain lysates. Thus, loss of the chaperone-like activity does not appear to account for the phenotype of Kvbeta2-null mice, which include reduced life spans, occasional seizures, and cold swim-induced tremors similar to that observed in Kv1.1-null mice. Mice expressing Kvbeta2, mutated at a site (Y90F) that abolishes AKR-like catalytic activity in other family members, have no overt phenotype. We conclude that Kvbeta2 contributes to regulation of excitability in vivo, although not directly through either chaperone-like or typical AKR catalytic activity. Rather, Kvbeta2 relies upon as yet unidentified mechanisms in the regulation of K(+) channel and/or oxidoreductive functions.

Animals↗
PubMed2002

Conditional disruption of beta 1 integrin in Schwann cells impedes interactions with axons.

In dystrophic mice, a model of merosin-deficient congenital muscular dystrophy, laminin-2 mutations produce peripheral nerve dysmyelination and render Schwann cells unable to sort bundles of axons. The laminin receptor and the mechanism through which dysmyelination and impaired sorting occur are unknown. We describe mice in which Schwann cell-specific disruption of beta1 integrin, a component of laminin receptors, causes a severe neuropathy with impaired radial sorting of axons. beta 1-null Schwann cells populate nerves, proliferate, and survive normally, but do not extend or maintain normal processes around axons. Interestingly, some Schwann cells surpass this problem to form normal myelin, possibly due to the presence of other laminin receptors such as dystroglycan and alpha 6 beta 4 integrin. These data suggest that beta 1 integrin links laminin in the basal lamina to the cytoskeleton in order for Schwann cells to ensheath axons, and alteration of this linkage contributes to the peripheral neuropathy of congenital muscular dystrophy.

Animals↗
PubMedDate not supplied

GFAP mutations in Alexander disease.

Alexander disease is a rare but often fatal disease of the central nervous system. Infantile, juvenile and adult forms have been described that present with different clinical signs, but are unified by the characteristic presence in astrocytes of Rosenthal fibers-protein aggregates that contain glial fibrillary acidic protein (GFAP) and small stress proteins. The chance discovery that mice expressing a human GFAP transgene formed abundant Rosenthal fibers suggested that mutations in the GFAP gene are a cause of Alexander disease. Sequencing results from several laboratories have indeed now identified GFAP coding mutations in most cases of the disease, including both the infantile and juvenile forms. These mutations have been found in the 1A, 2A and 2B segments of the conserved central rod domain of GFAP, and also in the variable tail region. All changes detected are heterozygous missense mutations, and none has been found in any parent of a patient that has been tested. This indicates that most cases of Alexander disease arise through de novo, dominant, GFAP mutations. Many of these mutations are homologous to ones described in other intermediate filament diseases. These other diseases have been attributed to a dominant loss of function, as the intermediate filament network is usually disrupted and a similar phenotype is observed in mice in which the corresponding intermediate filament gene has been inactivated. However, astrocytes of Alexander disease patients have normal appearing intermediate filaments, and GFAP null mice do not display the symptoms or pathology of Alexander disease. Thus, Alexander disease likely results from a dominant gain of function. Drawing upon the homology of many of the Alexander disease mutations to those found in other intermediate filament diseases, it is suggested that the gain of function is due to a partial block of filament assembly that leads to accumulation of an intermediate that participates in toxic interactions.

Alexander Disease↗