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J I Morgan

Publications and source records attributed to J I Morgan.

At least 37 records · Page 2Linked to original sources
PubMed1998

MPTP-Parkinsonism is accompanied by persistent expression of a delta-FosB-like protein in dopaminergic pathways.

Parkinson's disease (PD) is characterized by the relatively selective and progressive loss of dopaminergic neurons in the substantia nigra. During the early stages of PD, there are marked compensatory changes in the dopaminergic system, although little is known of how these responses are orchestrated. Since the induction of cellular immediate-early genes (cIEG) has been linked to adaptive responses in the nervous system, we examined their expression in the N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) murine model of PD. MPTP elicited an induction of c-fos, fosB, Delta-fosB and c-jun mRNAs in the striatum that persisted for 24 h. There was a parallel increase in AP-1-like DNA binding activity for up to 7 days post-treatment. At 7 days, AP-1 complexes were specifically supershifted with antisera to FosB and JunD. Immunoblotting of MPTP-treated striata with a FosB-specific antiserum revealed elevated levels of approximately 35 and approximately 46 kDa cross-reactive proteins. Only the 35 kDa protein was increased at 7 days. Thus, the persistent AP-1 complex seen in the MPTP-treated striatum is composed of JunD and a 35 kDa FosB-related protein, possibly Delta-FosB. In situ hybridization revealed elevated expression of fosB and Delta-fosB in the MPTP-treated brain. Expression of both transcripts was highest in ventral striatum, nucleus accumbens and other terminal fields of the mesolimbic system, such as the olfactory tubercle and Islands of Calleja. Thus, the increased fosB expression accompanying MPTP treatment was predominantly associated with dopaminergic pathways. Since FosB was expressed in both vulnerable and spared neuronal populations, we suggest that Delta-FosB-JunD heterodimers play a role in the adaptive response to MPTP neurotoxicity.

Aging↗
PubMed1998

Atm expression patterns suggest a contribution from the peripheral nervous system to the phenotype of ataxia-telangiectasia.

Ataxia-telangiectasia is a human autosomal recessive disease characterized by neurodegeneration, cancer predisposition and sensitivity to ionizing radiation. One of the earliest features of this disease is ataxia, which is thought to be attributable to a progressive cerebellar degeneration associated with a disruption of Purkinje cell cytoarchitecture and positioning. To investigate the neuropathology of ataxia-telangiectasia, we used in situ hybridization to map Atm (the gene mutated in ataxia-telangiectasia) expression during mouse development. Atm expression was highest in the embryonic mouse nervous system, where it was predominantly associated with regions undergoing mitosis. During the period of Purkinje cell neurogenesis, Atm was highly expressed in the area containing Purkinje cell precursors (the ventricular zone of the fourth ventricle). However, in the postnatal cerebellum, Atm expression in Purkinje cells was very low, while expression in proliferating granule neurons was high. The only region of the adult nervous system that exhibited elevated Atm expression were the postmitotic sensory neurons of the dorsal root ganglia. The data suggest an early developmental requirement for ATM in the cerebellum, and other regions of the central nervous system, and a potential contribution of the dorsal root ganglia/sensory input pathway to the ataxic phenotype of ataxia-telangiectasia.

Animals↗
PubMed1997

Effects of sleep on wake-induced c-fos expression.

We investigated the effects of sleep on wake-induced c-fos expression in the cerebral cortex of rats and c-fos-lacZ transgenic mice. In the cortex of rats, the levels of c-Fos, detected both by immunocytochemistry and Western blot, remained high during 6 or 12 hr of enforced wakefulness but declined rapidly (within 1 hr) with increasing time of recovery sleep. Similarly, in the transgenic mice in which lacZ expression is driven from the c-fos promoter, beta-galactosidase activity was high after enforced wakefulness and declined with increasing amounts of sleep. These results suggest that the decrease in c-Fos protein in cortical neurons during sleep may be attributable to cessation of c-fos expression, activation of a process that degrades the wake-induced c-Fos, or both.

Animals↗
PubMed1997

Absence of a persistently elevated 37 kDa fos-related antigen and AP-1-like DNA-binding activity in the brains of kainic acid-treated fosB null mice.

Chronic stimulation of the nervous system or acute administration of kainic acid results in a persistent increase in AP-1-like DNA-binding activity in the brain. However, the composition and function of these AP-1 complexes remain controversial. By comparing wild-type and fosB-null mice treated with kainic acid, we establish that the complexes comprise JunD in association with an approximately 37 kDa Delta-FosB species. Delta-FosB was expressed persistently in neurons in many areas of the CNS, even though fosB mRNA only increased transiently. This implies that the 37 kDa protein is very stable. fosB-/- mice are predisposed to seizures. Therefore, the chronic expression of Delta-FosB elicited by kainic acid seizures may be indicative of a compensatory/protective role in the pathophysiology of epilepsy.

Animals↗
PubMed1997

Modulation of cell death in yeast by the Bcl-2 family of proteins.

Bcl-2 family members are regulators of cell death. The precise biochemical properties of these proteins are unclear although intrafamily protein-protein association is thought to be involved. To elucidate structure-activity relationships among Bcl-2 proteins and identify the pathways in which they act, an inducible death suppressor assay was developed in yeast. Only Bax and Bak killed yeast via a process that did not require interleukin-1beta-converting enzyme-like proteases. Bax/Bak lethality was suppressed by coexpression of Bcl-2 family members that are anti-apoptotic in vertebrates, namely Bcl-xL, Bcl-2, Mcl-1, and A1. Furthermore, Bcl-xL and Bcl-2 suppressed Bax toxicity by distinct mechanisms in yeast. Bad, Bcl-xS, and Ced-9 lacked suppressor activity. These inactive proteins bound to anti-apoptotic members of the Bcl-2 family but not to Bax or Bak. In contrast, most Bcl-2 family proteins that attenuated death bound to Bax and Bak. However, two mutants of Bcl-xL suppressed Bax-induced cell death while having no Bax binding activity. Therefore, Bcl-xL functions independently of Bax binding, perhaps by interacting with a common target or promoting a pathway that antagonizes Bax. Thus, the pathways downstream of Bax and Bcl-xL may be conserved between vertebrates and yeast. This suppressor assay could be used to isolate components of these pathways.

Apoptosis↗
PubMed1997

USF2/FIP associates with the b-Zip transcription factor, c-Maf, via its bHLH domain and inhibits c-Maf DNA binding activity.

In screening for proteins that interact with the basic zipper (bZip) transcription factor, c-Maf, we isolated USF2/FIP. USF2 is a member of the bHLH-Zip protein family, possessing a basic (b) DNA binding region, a helix-loop-helix (HLH) motif, and a leucine zipper (Zip) structure. Mutants of USF2 that lacked a Zip formed heterodimers with c-Maf, but did not homodimerize. Deletion of the USF2 basic region or mutation of its helices abrogated its binding to c-Maf, but had no effect on homodimerization. A functional c-Maf bZip motif was necessary for both homodimerization and heterodimerization with USF2. These data suggest a tetrameric configuration for Maf-USF2 complexes. In the presence of USF2, the DNA binding activity of c-Maf was markedly reduced. Therefore, USF2 and c-Maf may interact to regulate gene expression.

Basic-Leucine Zipper Transcription Factors↗
PubMed1997

The Ca2+ binding protein, frequenin is a nervous system-specific protein in mouse preferentially localized in neurites.

Frequenin is a Ca2+-binding protein that has been implicated in the regulation of neurotransmitter release at the neuromuscular junction [15,16]. However, its cellular and subcellular localization in brain have not been determined. Therefore, we cloned mouse frequenin (Mfreq) and investigated its expression both in vivo and in vitro. The amino acid sequence of Mfreq is homologous to that of frequenins from other species. Northern and Western blot analyses indicated that the Mfreq mRNA is a single species of 4.2 kb, and that the protein has a mass of 24 kDa protein on SDS gel, respectively. Expression of Mfreq is nervous system specific. However, Mfreq mRNA and protein are widely distributed in the brain, spinal cord, and dorsal root ganglia. Mfreq is expressed in early embryonic brain and the levels of Mfreq remain high throughout development. In situ hybridization and immunocytochemistry demonstrated that Mfreq is expressed primarily in neurons and presumptive astrocytes. The Mfreq protein was preferentially localized in neurites (dendrites and axons). Double immunofluorescence microscopy established that Mfreq was co-localized with the dendritic marker, MAP-2 and the synapse marker, SV2 in cultured hippocampal neurons. The distribution and subcellular localization of Mfreq may help understand its cellular function.

Amino Acid Sequence↗
PubMed1997

Absence of neuroanatomical and behavioral deficits in L7/pcp-2-null mice.

L7/pcp-2 is expressed exclusively in cerebellar Purkinje and retinal bipolar neurons. While the function of L7/pcp-2 is unknown, its mRNA is trafficked into dendrites, suggesting a role in dendritic physiology. To elucidate its function, L7/pcp-2-null mice were generated. These mice are neurologically normal with no signs of cerebellar or retinal dysfunction. The mice are indistinguishable from wild-type littermates with regards to gross neuroanatomy and fine structure of Purkinje cell dendrites.

Animals↗
PubMed1997

Transgenic approaches to cerebellar development.

The advent of transgenic mouse technology and the harnessing of homologous recombination to eliminate genes in living animals have provided powerful new approaches to investigate some of the fundamental issues in developmental neurobiology. In this chapter we illustrate several examples of the use of these technologies to investigate the murine cerebellum. These range from using inert, marker transgenes to follow the organization strategy of the cerebellum, to eliminating specific cell populations and modifying the function and fate of Purkinje cells. Finally, we provide a perspective on future extensions of these transgenic approaches.

Animals↗
PubMed1996

Correspondence between L7-lacZ-expressing Purkinje cells and labeled olivocerebellar fibers during late embryogenesis in the mouse.

It has been suggested that Purkinje cells (PC) play a role in organizing topographic relationships of several cerebellar afferent systems, including olivocerebellar fibers. This hypothesis is based on the observation that PC in the rat express biochemical heterogeneities during the presumptive period of olivocerebellar fiber ingrowth to the cerebellum. Previous studies designed to investigate the organization of murine olivocerebellar fibers during embryogenesis have suggested that interactions with PC may play a role in segregating olivocerebellar fibers after they enter the cerebellum. To determine whether PC heterogeneities are related to olivocerebellar fiber organization, transgenic mice carrying a beta-galactosidase (beta-gal) reporter gene linked to the promoter from the PC-specific gene L7/pcp-2 were used in neuroanatomical tracing experiments. Expression of the transgene mirrors endogenous L7/pcp-2 expression, which is upregulated earliest in parasagittal strips of the vermal cortex. Studies were conducted in vitro by using brainstem-cerebellar explants from embryonic day 17/18 (E17/18) and 18/19 mice. Applications of neuroanatomical tracer (horseradish peroxidase or neurobiotin) were made in either the caudal medial accessory olive (cMAO) or the rostral olive. These studies indicate that groups of olivocerebellar fibers and clusters of L7/lacZ+ and L7/lacZ-Purkinje cells respect common distribution boundaries during late embryogenesis. The strong correspondence between the distribution patterns generated by these two markers suggests that expression of L7/pcp-2 and the topographic organization of olivocerebellar (OC) fibers are not interdependent, but may be regulated by a common event or interaction, of a presently unknown nature, which occurs earlier during cerebellar development.

Animals↗
PubMed1996

Camstatins are peptide antagonists of calmodulin based upon a conserved structural motif in PEP-19, neurogranin, and neuromodulin.

Unbridled increases in intracellular ionized calcium can result in neuronal damage and death. Since many of the deleterious effects of calcium are mediated by calmodulin, we have sought to identify neuronal proteins that inhibit activation of this ubiquitous protein. PEP-19 is a 7.6-kDa neuron-specific protein, which contains a motif similar to the calmodulin binding domains of neuromodulin (GAP-43) and neurogranin (RC3). Here we show that PEP-19 binds calmodulin in an analogous calcium-independent manner with an apparent Kd near 1.2 microM. Furthermore, using the calmodulin-dependent enzyme neuronal nitric oxide synthase, we demonstrate that native PEP-19 is also an antagonist of enzyme activity. Based on the PEP-19 sequence, a series of peptide calmodulin antagonists termed camstatins were synthesized. These analogs define the minimally active domain of PEP-19 and provide a structure/activity relationship for calmodulin antagonism. There was a positive correlation between the binding affinities of the camstatins for calmodulin and their potencies as neuronal nitric oxide synthase inhibitors. Despite the similar IQ motif in PEP-19 and neuromodulin or neurogranin, PEP-19 was not a substrate for protein kinase C. The properties of PEP-19 suggest that it could fulfill a role in neuroprotection.

Amino Acid Sequence↗
PubMed1996

Developmental expression of Fos-lacZ in the brains of postnatal transgenic rats.

Previously, we reported the production and characterization of fos-lacZ transgenic mice [41] and rats [19] that can be used to monitor both constitutive and evoked expression of c-fos in vivo. When we compared the sites of spontaneous fos-lacZ expression in the brains of developing transgenic fos-lacZ mice and rats, the patterns were almost identical. However, throughout the first postnatal month, the rat striatum contained a large number of Fos-lacZ-positive cells whereas only a few positive cells were seen in the mouse. By adulthood, the number of Fos-lacZ-positive cells in the rat striatum had declined dramatically to the low basal values seen in mice. To establish whether this species difference was evident in the adult striatum, rats and mice were treated with metamphetamine. This indirect D1 agonist, triggered a pronounced induction of fos-lacZ in the rat striatum while only a modest response was observed in the mouse. These data imply: (1) there are differences in dopamine-dependent stimulus-transcription coupling between the two species. (2) Maturation of dopaminergic signalling pathways may underlie the spontaneous immediate-early gene response in the developing rat striatum.

Amphetamines↗
PubMed1996

Analysis of interaction sites in homo- and heteromeric complexes containing Bcl-2 family members and the cellular prion protein.

The cellular prion protein (PrP) binds to the C-terminus of Bcl-2 but not Bax. Therefore, we examined whether the C-terminus of Bcl-2 was important for other homomeric and heteromeric protein-protein interactions. Using the yeast two hybrid system and co-immunoprecipitation, three sites of homomeric interactions were identified within Bcl-2. The carboxy terminal 37 amino acids selectively homodimerized. Two additional regions of Bcl-2 (residues 1-129 and 126-200) interacted with each other, but not themselves permitting both intra- and intermolecular association. In addition, we analyzed heteromeric interactions of Bcl-2 with PrP and two Bcl-2 related proteins, Bax and A1. The domain requirements for binding of those three proteins to Bcl-2 were different from one another. Bax binding required almost the entire Bcl-2 molecule, while A1 bound to the amino terminal region (residues 1-82). PrP associated with the carboxy terminus of Bcl-2 (amino acids 200-236). These data suggest configurational models for Bcl-2 containing complexes. First, Bcl-2 may exist as both heterodimers and heteromultimers. Second, molecules such as Bax and A1 may serve to cap chains of Bcl-2 homodimers by interacting with dimerization domains in the extramembrane region. PrP may disrupt chains of Bcl-2 molecules at the homomeric association site in the transmembrane region.

Hybrid Cells↗
PubMed1996

The impact of a confusion technique on hypnotic responsivity in low-susceptible subjects.

The present study investigated the hypothesis that a confusion technique would produce greater hypnotic responsiveness for subjects who responded minimally to a standard hypnotic induction. Ten subjects who scored in the low range of hypnotic susceptibility on the HGSHS:A (scores of 0-4) participated in a confusion induction session. Hypnotic responsiveness was measured by several scales: the Harvard Group Scale of Hypnotic Susceptibility (HGSHS:A), a Depth Estimate (DE), and the Inventory Scale of Hypnotic Depth (ISHD). Qualitative data was collected via a follow-up interview. Collectively, the results did not support the hypothesis that a confusion technique is more effective than a standard induction for low-susceptible subjects. Implications for future research will be discussed.

Adolescent↗
PubMed1996

C/EBPalpha regulation of the growth-arrest-associated gene gadd45.

CCAAT/enhancer-binding protein alpha (C/EBPalpha) is expressed in postmitotic, differentiated adipocytes and is required for adipose conversion of 3T3-L1 cells in culture. Temporal misexpression of C/EBPalpha in undifferentiated adipoblasts leads to mitotic growth arrest. We report here that growth arrest- and DNA damage-inducible gene 45 (gadd45) is preferentially expressed in differentiated 3T3-L1 adipocytes similar to phenotype-associated genes. Furthermore, C/EBPalpha transactivates a reporter plasmid containing 1.5 kb of the gadd45 promoter region. The proto-oncogene myc, which inhibits adipocyte differentiation, abrogates C/EBPalpha activation of gadd45. gadd45 is known to be a target of the tumor suppressor p53 in a G1 checkpoint activated by DNA damage. Immunoprecipitation of radiolabeled proteins with conformation-specific antibodies revealed that wild-type p53 is expressed throughout 3T3-L1 adipocyte development, including the postmitotic period characterized by the accumulation of gadd45 and C/EBPalpha. A stable 3T3-L1 subline was engineered to express a dominant negative p53, human p53(143ala). The p53(143ala) subline differentiated to adipocytes and showed appropriate developmental expression of gadd45. These findings suggest that postmitotic growth arrest is coupled to adipocyte differentiation via C/EBPalpha stimulation of growth arrest-associated and phenotype-associated genes.

3T3 Cells↗
PubMed1995

Spontaneous and evoked glutamate signalling influences Fos-lacZ expression and pyramidal cell death in hippocampal slice cultures from transgenic rats.

Previously, we established that a spatially and temporally predictable pattern of spontaneous cell death occurs in pyramidal hippocampal neurons maintained in organotypic slice cultures. We have begun to examine the signalling events that may be relevant to this process by analyzing the expression of cellular immediate-early genes (cIEGs). In the present studies, organotypic hippocampal cultures were generated from transgenic rats that carry a fos-lacZ fusion gene. beta-Galactosidase activity in these rats accurately recapitulates Fos expression. An association was observed between cell death, as determined by propidium iodide (PI) staining, and Fos-lacZ expression. There was a consistent rise in beta-galactosidase activity in vulnerable regions 1-2 days before the peak of spontaneous neuronal death. Long-term treatment with TTX, CNQX, or D,L-APV inhibited the spontaneous neuronal death as well as Fos-lacZ expression. Furthermore, Fos-lacZ induction and cell death could be evoked by removal of these receptor antagonists or by application of the excitotoxin, kainic acid. The association between cIEG expression and cell death, shown here and by others, suggests that these genes contribute to regulatory events involved with cell death and/or protection.

Animals↗