PubMed Health⌕ Search

Biomedical subjects

M E MacDonald

Publications and source records attributed to M E MacDonald.

At least 19 recordsLinked to original sources
PubMed1997

Heterogeneous topographic and cellular distribution of huntingtin expression in the normal human neostriatum.

A striking heterogeneous distribution of topographic and cellular huntingtin immunoreactivity was observed within the human neostriatum using three distinct huntingtin antibodies. Patchy areas of low huntingtin immunoreactivity were present in both the caudate nucleus and putamen, surrounded by an intervening area of greater immunoreactivity. Comparison of huntingtin immunoreactivity with contiguous serial sections stained for enkephalin and calbindin D28k immunoreactivities showed that the topographic heterogeneity of huntingtin immunostaining corresponded to the patch (striosome) and matrix compartments within the striatum. Huntingtin immunoreactivity was confined primarily to neurons and neuropil within the matrix compartment, whereas little or no neuronal or neuropil huntingtin immunostaining was observed within the patch compartment. There was marked variability in the intensity of huntingtin immunolabel among medium-sized striatal neurons, whereas a majority of large striatal neurons were only faintly positive or without any immunoreactivity. Combined techniques for NADPH-diaphorase enzyme histochemistry and huntingtin immunocytochemistry, as well as double immunofluorescence for either nitric oxide synthase or calbindin D28k in comparison with huntingtin expression, revealed a striking correspondence between calbindin D28k and huntingtin immunoreactivities, with little or no colocalization between NADPH-diaphorase or nitric oxide synthase neurons and huntingtin expression. These observations suggest that the selective vulnerability of spiny striatal neurons and the matrix compartment observed in Huntington's disease is associated with higher levels of huntingtin expression, whereas the relative resistance of large and medium-sized aspiny neurons and the patch compartments to degeneration is associated with low levels of huntingtin expression.

Aged↗
PubMed1997

CAG repeat number governs the development rate of pathology in Huntington's disease.

We compared the number of CAG repeats, the age at death, and the severity of neuropathology in 89 Huntington's disease brains. We found a linear correlation between the CAG repeat number and the quotient of the degree of atrophy in the striatum (the brain region most severely affected in Huntington's disease) divided by age at death, with an intercept at 35.5 repeats. The largest CAG repeat length, therefore, at which no pathology is expected to develop is 35.5. These results imply that striatal damage in Huntington's disease is almost entirely a linear function of the length of the polyglutamine stretch beyond 35.5 glutamines multiplied by the age of the patient. Thus, it is predicted that the pathological process develops linearly from birth. Analysis of other measures of striatal function could test this hypothesis and might determine when treatment for CAG repeat diseases should start.

Adult↗
PubMed1997

Frataxin gene of Friedreich's ataxia is targeted to mitochondria.

Friedreich's ataxia is caused by a triplet repeat expansion in intron 1, a noncoding region of the frataxin gene (X25). We have generated a chimeric gene composed of the frataxin gene fused with the green fluorescent protein (GFP) gene as a reporter. Transfection of the fusion construct into living COS cells revealed that the frataxin-GFP construct localizes to organelles that double-label with 8-(4'-chloromethyl) phenyl-2,3,5,6,11,12,14,15-octahydro-1H,4H,10H-13H-diquinolizin o-8H-xanthylium chloride (CMXRos), a novel mitochondrial dye. Thus, frataxin appears to be a nuclear-encoded mitochondrial protein.

Animals↗
PubMed1997

Assignment of the human gene encoding eukaryotic initiation factor 4E (EIF4E) to the region q21-25 on chromosome 4.

We recently cloned genomic sequences containing the promoter region for the messenger RNA cap binding protein (eIF4E). As the rate-limiting step in translation, eukaryotic initiation factor 4E is important in cellular growth control. Using oligonucleotide primers specific for the promoter region in polymerase chain reactions (PCR), we amplified the human gene in a chromosome 4-specific human/rodent somatic cell panel. This panel mapped single copy genomic sequences for eIF4E in the region 4q21 to 4q25.

Animals↗
PubMed1997

Reduced penetrance of the Huntington's disease mutation.

Controversy persists concerning the significance of Huntington disease (HD) alleles in the 36-39 repeat range. Although some clinically affected persons have been documented with repeats in this range, elderly unaffected individuals have also been reported. We examined 10 paternal transmissions of HD alleles of 37-39 repeats in collateral branches of families with de novo HD. All 10 descendants, including many who are elderly, are without symptoms of HD. Forty percent of the transmissions were unstable, although none varied by more than one repeat. The observation that individuals with alleles of 37-39 repeats may survive unaffected beyond common life expectancy supports the presence of reduced penetrance for HD among some persons with repeat sizes which overlap the clinical range. Non-penetrance may be increased in the collateral branches of de novo mutation families when compared to penetrance estimates from patient series. There was no CAA-->CAG mutation for the penultimate glutamine in either a de novo expanded 42 repeat allele or the corresponding non-penetrant 38 repeat allele in a family with fresh mutation to HD.

Adult↗
PubMed1996

Homozygous defect in HIV-1 coreceptor accounts for resistance of some multiply-exposed individuals to HIV-1 infection.

Rare individuals have been multiply exposed to HIV-1 but remain uninfected. The CD4+ T-cells of two of these individuals, designated EU2 and EU3, are highly resistant in vitro to the entry of primary macrophagetropic virus but are readily infectable with transformed T-cell line adapted viruses. We report here on the genetic basis of this resistance. We found that EU2 and EU3 have a homozygous defect in CKR-5, the gene encoding the recently described coreceptor for primary HIV-1 isolates. These individuals appear to have inherited a defective CKR-5 allele that contains an internal 32 base pair deletion. The encoded protein is severely truncated and cannot be detected at the cell surface. Surprisingly, this defect has no obvious phenotype in the affected individuals. Thus, a CKR-5 allele present in the human population appears to protect homozygous individuals from sexual transmission of HIV-1. Heterozygous individuals are quite common (approximately 20%) in some populations. These findings indicate the importance of CKR-5 in HIV-1 transmission and suggest that targeting the HIV-1-CKR-5 interaction may provide a means of preventing or slowing disease progression.

Alleles↗
PubMed1996

Characterization of the G protein-coupled receptor kinase GRK4. Identification of four splice variants.

A novel human G protein-coupled receptor kinase was recently identified by positional cloning in the search for the Huntington's disease locus (Ambrose, C., James, M., Barnes, G., Lin, C., Bates, G., Altherr, M., Duyao, M., Groot, N., Church, D., Wasmuth, J. J., Lehrach, H., Housman, D., Buckler, A., Gusella, J. F., and MacDonald, M. E. (1993) Hum. Mol. Genet. 1, 697-703). Comparison of the deduced amino acid sequence of GRK4 with those of the closely related GRK5 and GRK6 suggested the apparent loss of 32 codons in the amino-terminal domain and 46 codons in the carboxyl-terminal domain of GRK4. These two regions undergo alternative splicing in the GRK4 mRNA, resulting from the presence or absence of exons filling one or both of these apparent gaps. Each inserted sequence maintains the open reading frame, and the deduced amino acid sequences are similar to corresponding regions of GRK5 and GRK6. Thus, the GRK4 mRNA and the GRK4 protein can exist as four distinct variant forms. The human GRK4 gene is composed of 16 exons extending over 75 kilobase pairs of DNA. The two alternatively spliced exons correspond to exons II and XV. The genomic organization of the GRK4 gene is completely distinct from that of the human GRK2 gene, highlighting the evolutionary distance since the divergence of these two genes. Human GRK4 mRNA is expressed highly only in testis, and both alternative exons are abundant in testis mRNA. The four GRK4 proteins have been expressed, and all incorporate [3H]palmitate. GRK4 is capable of augmenting the desensitization of the rat luteinizing hormone/chorionic gonadotropin receptor upon coexpression in HEK293 cells and of phosphorylating the agonist-occupied, purified beta2-adrenergic receptor, indicating that GRK4 is a functional protein kinase.

Alternative Splicing↗
PubMed1996

Differential expression of normal and mutant Huntington's disease gene alleles.

Huntingtin expression was examined by Western blot and immunoprecipitation studies of lymphoblastoid cell lines from Huntington's disease (HD) homozygotes, heterozygotes, and a phenotypically normal individual with a t(4p16.3;12p13.3) breakpoint in the HD gene. The latter produced a reduced level of normal huntingtin without evidence of an altered protein, indicating that simple loss of huntingtin activity does not cause HD. In juvenile onset HD heterozygotes, NH2- and COOH-terminal antisera revealed reduced relative expression from the mutant allele. Pulse-chase studies indicated that huntingtin is a stable protein whose differential allelic expression is not due to destabilization of the mutant isoform. No stable breakdown products specific to mutant huntingtin were detected in either HD homozygotes or heterozygotes. These data are consistent with HD involving either a gain of function or a dominant negative loss of function that operates within severe constraints and suggest that in either case the pathogenic process is usually saturated by the amount of abnormal huntingtin produced from a single mutant allele.

Adult↗
PubMed1996

Coexistence of Huntington's disease and familial amyotrophic lateral sclerosis: case presentation.

We present the clinical, molecular genetic and neuropathological findings of an 81-year-old man with concurrent Huntington's disease (HD) and familial amyotrophic lateral sclerosis (FALS). His mother had been diagnosed clinically as having ALS. There was no known family history of HD, but a maternal uncle had died in a chronic care psychiatric hospital. The diagnosis of HD in the patient was suspected at age 66, after 8 years of personality change, hallucinations, agitation, cognitive decline and choreoathetosis. No symptoms of motor neuron disease were noticed at that time, but progressive weakness developed later. Postmortem examination revealed cerebral atrophy, marked atrophy of basal ganglia (grade 3), and atrophy of brain stem and spinal cord. The neostriatum displayed massive neuronal loss and gliosis. The neocortex showed changes characteristic of Alzheimer's disease. Pathological lesions also included loss of neurons and gliosis in the anterior horns, Clarke's columns and the hypoglossal nuclei; degeneration of the lateral corticospinal tracts, dorsal spinocerebellar tracts and fasciculus gracilis; and rare Bunina bodies and ubiquitin-positive filamentous skeins in motor-neuron perikarya. Molecular analysis demonstrated chromosome 4p16.3 expansion of trinucleotide repeats characteristic of HD. Analysis of Cu,Zn superoxide dismutase gene and heavy neurofilament subunit gene failed to demonstrate mutations. The concurrence of HD and FALS in our patient and three previously reported cases did not appear to be associated with cosegregation in other family members.

Aged↗
PubMed1996

Huntington's disease: translating a CAG repeat into a pathogenic mechanism.

The specific pattern of neuronal cell death in Huntington's disease (HD) is triggered by an abnormal version of the huntingtin protein, which is produced by translation of the HD gene defect, an expanded CAG repeat in a novel 4p16.3 gene. The extended amino-terminal polyglutamine segment may act via the protein's inherent activity, increasing it or decreasing it in a graded fashion, or, alternatively, it may confer the ability to interact with a completely different set of cellular pathways, focusing attention on the HD protein's normal and abnormal physiological functions.

Animals↗
PubMed1996

Trinucleotide instability: a repeating theme in human inherited disorders.

In recent years, a completely new mechanism of mutation has emerged in a number of disorders that display perplexing and paradoxical features of genetic inheritance. This mechanism involves the expansion and intergenerational instability of stretches of consecutive identical nucleotide triplets that also exist as shorter stable segments on normal chromosomes. The unstable nature of the trinucleotide segments has solved many of the genealogic puzzles in these disorders and has provided a new tool for predictive testing. Treatments for the disorders await a better understanding of the different pathogenic processes that are triggered by various expanded repeats. The existence of numerous other disorders with peculiarities of genetic inheritance suggests that this mutational mechanism may be a major cause of human inherited disease.

Chromosome Aberrations↗
PubMed1995

Huntington's disease: CAG genetics expands neurobiology.

Huntington's disease, with its progressive uncontrolled movements and characteristic selective neuropathology, has represented a baffling enigma to geneticists and neurobiologists alike. Discovery of the HD gene and its defect has demystified the genetic aspects of the disorder, but has not yet explained its pathogenesis. Attempts to explore this issue suggest that the defect acts as a gain of function, conferring a new deleterious property on the huntingtin protein, and that the gene's normal function may be irrelevant to the disease process.

Amino Acid Sequence↗
PubMed1995

Huntington's disease.

Early in 1993, an unstable, expanded trinucleotide repeat in a novel gene of unknown function was identified on HD chromosomes. This discovery unleased a flurry of experimentation that has established the expanded CAG repeat the almost universal cause of the characteristic neurologic symptoms and pathology of this neurodegenerative disorder of midlife onset. The biochemical basis for the specific neuronal loss of HD remains uncertain, but the genetic lesion probably acts via its consequent polyglutamine segment in the protein product, huntingtin. This review will describe the basic parameters of the HD repeat's behavior and the knowledge that has accumulated concerning its potential mechanisms of action.

Age of Onset↗
PubMed1995

Single sperm analysis of the trinucleotide repeats in the Huntington's disease gene: quantification of the mutation frequency spectrum.

The CAG triplet repeat region of the Huntington's disease gene was amplified in 923 single sperm from three affected and two normal individuals. Average-size alleles (15-18 repeats) showed only three contraction mutations among 475 sperm (0.6%). A 30 repeat normal allele showed an 11% mutation frequency. The mutation frequency of a 36 repeat intermediate allele was 53% with 8% of all gametes having expansions which brought the allele size into the HD disease range (> or = 38 repeats). Disease alleles (38-51 repeats) showed a very high mutation frequency (92-99%). As repeat number increased there was a marked elevation in the frequency of expansions, in the mean number of repeats added per expansion and the size of the largest observed expansion. Contraction frequencies also appeared to increase with allele size but decreased as repeat number exceeded 36. Our sperm typing data are of a discrete nature rather than consisting of smears of PCR product from pooled sperm. This allowed the observed mutation frequency spectra to be compared to the distribution calculated using discrete stochastic models based on current molecular ideas of the expansion process. An excellent fit was found when the model specified that a random number of repeats are added during the progression of the polymerase through the repeated region.

Alleles↗