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J Nasir

Publications and source records attributed to J Nasir.

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

Gene structure and map location of the murine homolog of the Huntington-associated protein, Hap1.

Huntington's Disease (HD) is an inherited progressive neurodegenerative disorder associated with a mutation in a gene expressed in both affected and non-affected tissues. The selective neuropathology in HD is thought to be mediated in part through interactions with other proteins including the Huntington Associated Protein, HAP-1, which is predominantly expressed in the brain. We have mapped its murine homolog, Hap1, to mouse Chr 11 (band D), which shares extensive synteny with human Chr 17 including the region 17q21-q22, where the gene for 'frontotemporal dementia and parkinsonism linked to chromosome 17' has bee mapped. In addition, we have sequenced a 21,984 base pair (bp) genomic clone encompassing the entire Hap1 gene. It is organized as 11 exons and flanked by exons from potentially one or more novel genes. At least three Hap1 transcripts (Hap1-A; Hap1-B; Hap1-C) can be formed by alternative splicing at the 3' end of the gene leading to protein isoforms with novel C-termini.

Algorithms↗
PubMed1998

Cell death attenuation by 'Usurpin', a mammalian DED-caspase homologue that precludes caspase-8 recruitment and activation by the CD-95 (Fas, APO-1) receptor complex.

Apoptotic cell suicide initiated by ligation of CD95 (Fas/APO-1) occurs through recruitment, oligomerization and autocatalytic activation of the cysteine protease, caspase-8 (MACH, FLICE, Mch5). An endogenous mammalian regulator of this process, named Usurpin, has been identified (aliases for Usurpin include CASH, Casper, CLARP, FLAME-1, FLIP, I-FLICE and MRIT). This protein is ubiquitously expressed and exists as at least three isoforms arising by alternative mRNA splicing. The Usurpin gene is comprised of 13 exons and is clustered within approximately 200 Kb with the caspase-8 and -10 genes on human chromosome 2q33-34. The Usurpin polypeptide has features in common with pro-caspase-8 and -10, including tandem 'death effector domains' on the N-terminus of a large subunit/small subunit caspase-like domain, but it lacks key residues that are necessary for caspase proteolytic activity, including the His and Cys which form the catalytic substrates diad, and residues that stabilize the P1 aspartic acid in substrates. Retro-mutation of these residues to functional caspase counterparts failed to restore proteolytic activity, indicating that other determinants also ensure the absence of catalytic potential. Usurpin heterodimerized with pro-caspase-8 in vitro and precluded pro-caspase-8 recruitment by the FADD/MORT1 adapter protein. Cell death induced by CD95 (Fas/APO-1) ligation was attenuated in cells transfected with Usurpin. In vivo, a Usurpin deficit was found in cardiac infarcts where TUNEL-positive myocytes and active caspase-3 expression were prominent following ischemia/reperfusion injury. In contrast, abundant Usurpin expression (and a caspase-3 deficit) occurred in surrounding unaffected cardiac tissue, suggesting reciprocal regulation of these pro- and anti-apoptotic molecules in vivo. Usurpin thus appears to be an endogenous modulator of apoptosis sensitivity in mammalian cells, including the susceptibility of cardiac myocytes to apoptotic death following ischemia/ reperfusion injury.

Alternative Splicing↗
PubMed1997

Spontaneous recovery of chemotherapy-induced primary ovarian failure: implications for management.

A 14-year-old female patient presented with a swelling, which was excised, over the left forearm. Histology revealed a poorly differentiated rhabdomyosarcoma and she was treated with multiple chemotherapy for 2 years, including cyclophosphamide, cisplatin and vincristine. She developed secondary amenorrhoea shortly after commencing treatment which persisted on its completion. Biochemical investigations were consistent with ovarian failure, which was assumed to be chemotherapy-induced and permanent. She was given hormone replacement with a conjugated equine oestrogen/norgestrel combination, resulting in regular withdrawal bleeding. At 22 years of age; she presented with amenorrhoea for 3 months. Investigations revealed FSH 2.7 IU/l, LH > 50 IU/l and oestradiol > 1320 pmol/l. A pregnancy test was positive and subsequent ultrasound scanning confirmed the presence of a foetus of 18 weeks gestation. The patient initially considered a termination as she had been unprepared for this event but later elected to continue the pregnancy which proceeded uneventfully and resulted in the birth of a normal infant. Ovarian function should be reassessed periodically in patients with chemotherapy-induced gonadal damage and/or the oral contraceptive pill should be used as hormone replacement unless fertility is desired.

Adolescent↗
PubMed1996

11 beta-hydroxylase deficiency: management of a difficult case by laparoscopic bilateral adrenalectomy.

A 14-year-old girl presented with short stature and progressive virilization. She had not undergone the menarche. On investigation, she had elevated testosterone, androstenedione, dihydroepiandrosterone sulphate and 17 alpha-hydroxyprogesterone levels, which were all suppressed by overnight dexamethasone to within their normal ranges. An initial diagnosis of 21-hydroxylase deficiency was revised to 11 beta-hydroxylase deficiency after a tetracosactrin stimulation test, which showed only a modest rise in 17 alpha-hydroxyprogesterone level (from 92 nmol/l at baseline to 133 nmol/l at 60 minutes) and measurement of the basal 11-deoxycortisol, which was grossly elevated. Treatment with dexamethasone 0.5 mg nocte resulted in suppression of androgens in the daytime, but not in the evening, particularly androstenedione. Treatment with hydrocortisone 10 mg b.d. failed to suppress testosterone or androstenedione over a 24-hour period. Addition of cyproterone and oestrogen supplements had no effect and significant virilization persisted. Laparoscopic bilateral adrenalectomy was therefore performed as definitive treatment and resulted in remarkable clinical and biochemical improvement. This case illustrates difficulties in correct diagnosis, choice of appropriate steroid regimen and monitoring efficacy of treatment in congenital adrenal hyperplasia due to 11 beta-hydroxylase deficiency. More aggressive management with earlier bilateral adrenalectomy may be appropriate in selected cases.

Adolescent↗
PubMed1996

Human huntingtin derived from YAC transgenes compensates for loss of murine huntingtin by rescue of the embryonic lethal phenotype.

Huntington disease (HD) is caused by expansion of a CAG trinucleotide repeat in exon 1 of a novel gene. The HD protein (huntingtin) plays a critical role in early embryonic development since homozygous targeted disruption of the murine HD gene results in embryonic lethality by day 7.5. To rescue this phenotype by transgene based huntingtin expression it is therefore essential to express the protein early enough in development in the appropriate cells. Since YAC based transgenes are known to be regulated in an appropriate temporal and tissue-specific manner, we sought to rescue the embryonic lethality by breeding YAC transgenic mice expressing human huntingtin with mice heterozygous for the targeted disruption. We generated viable offspring homozygous for the disrupted murine HD gene but expressing human huntingtin derived from the YAC. This result clearly shows that YAC transgene based expression of huntingtin occurs prior to 7.5 days gestation. Additionally, we show that human huntingtin expression in YAC transgenic mice follows an identical tissue distribution and subcellular localisation pattern as that of the murine endogenous protein and that expression levels of 2-3 times endogenous can be achieved. This shows that human huntingtin under the influence of its native promoter, despite differences to the murine protein, is functional in a murine background and can compensate for loss of the murine protein. These results show that YAC transgenic approaches are a particularly promising route to producing an animal model for disorders associated with CAG expansion.

Animals↗
PubMed1996

Absence of disease phenotype and intergenerational stability of the CAG repeat in transgenic mice expressing the human Huntington disease transcript.

The mutation underlying Huntington disease (HD) is CAG expansion in the first exon of the HD gene. In order to investigate the role of CAG expansion in the pathogenesis of HD, we have produced transgenic mice containing the full length human HD cDNA with 44 CAG repeats. By 1 year, these mice have no behavioral abnormalities and morphometric analysis at 6 (one animal) and 9 (two animals) months age revealed no changes. Despite high levels of mRNA expression, there was no evidence of the HD gene product in any of these transgenic mice. In vitro transfection studies indicated that the inclusion of 120 bp of the 5' UTR in the cDNA construct and the presence of a frameshift mutation at nucleotide 2349 prevented expression of the HD cDNA. These findings suggest that the pathogenesis of HD is not mediated through DNA-protein interaction and that presence of the RNA transcript with an expanded CAG repeat is insufficient to cause the disease. Rather, translation of the CAG is crucial for the pathogenesis of HD. In contrast to that seen in humans, the CAG repeat in these mice was remarkably stable in 97 meioses. This suggests that genomic sequences may play a critical role in influencing repeat instability.

Animals↗
PubMed1996

Huntington disease: new insights into the relationship between CAG expansion and disease.

The mutation underlying Huntington disease (HD) is CAG expansion beyond 35 repeats within a novel gene. Recently, new insights into the role of the HD protein (huntingtin) in the pathogenesis of HD have emerged. The CAG is translated and expression of mutant huntingtin is essential for neuronal death. Huntingtin is crucial for normal development and may be regarded as a cell survival gene. Huntingtin is specifically cleaved during apoptosis by a key cysteine protease, apopain, known to play a pivotal role in apoptotic cell death. The rate of cleavage is enhanced by longer polyglutamine tracts, suggesting that inappropriate apoptosis underlies HD. Recently, three proteins have been identified and have been shown specifically to interact with huntingtin, two of these interactions being influenced by CAG length. Several different approaches to develop an animal model for HD include cDNA and YAC transgenics, as well as 'knock-in' strategies. Such a model will be critical for the understanding of the natural history of HD and for the testing of new therapeutic modalities.

Animals↗
PubMed1995

Targeted disruption of the Huntington's disease gene results in embryonic lethality and behavioral and morphological changes in heterozygotes.

Huntington's disease (HD) is an incurable neuropsychiatric disease associated with CAG repeat expansion within a widely expressed gene that causes selective neuronal death. To understand its normal function, we have created a targeted disruption in exon 5 of Hdh (Hdhex5), the murine homolog of the HD gene. Homozygotes die before embryonic day 8.5, initiate gastrulation, but do not proceed to the formation of somites or to organogenesis. Mice heterozygous for the Hdhex5 mutation display increased motor activity and cognitive deficits. Neuropathological assessment of two heterozygous mice shows significant neuronal loss in the subthalamic nucleus. These studies show that the HD gene is essential for postimplantation development and that it may play an important role in normal functioning of the basal ganglia.

Animals↗
PubMed1995

Structural analysis of the 5' region of mouse and human Huntington disease genes reveals conservation of putative promoter region and di- and trinucleotide polymorphisms.

We have previously cloned and characterized the murine homologue of the Huntington disease (HD) gene and shown that it maps to mouse chromosome 5 within a region of conserved synteny with human chromosome 4p16.3. Here we present a detailed comparison of the sequence of the putative promoter and the organization of the 5' genomic region of the murine (Hdh) and human HD genes encompassing the first five exons. We show that in this region these two genes share identical exon boundaries, but have different-size introns. Two dinucleotide (CT) and one trinucleotide intronic polymorphism in Hdh and an intronic CA polymorphism in the HD gene were identified. Comparison of 940-bp sequence 5' to the putative translation start site reveals a highly conserved region (78.8% nucleotide identity) between Hdh and the HD gene from nucleotide -56 to -206 (of Hdh). Neither Hdh nor the HD gene have typical TATA or CCAAT elements, but both show one putative AP2 binding site and numerous potential Sp1 binding sites. The high sequence identity between Hdh and the HD gene for approximately 200 bp 5' to the putative translation start site indicates that these sequences may play a role in regulating expression of the Huntington disease gene.

Animals↗
PubMed1995

Genomic organization of the human alpha-adducin gene and its alternately spliced isoforms.

The cDNA for the human alpha-adducin gene has been cloned, and different alternately spliced forms have been identified. We report the complete genomic organization of the human alpha-adducin gene and these alternately spliced forms. The human alpha-adducin gene, spanning approximately 85 kb, consists of 16 exons ranging in size from 34 to 1892 bp. One of the spliced forms of the human alpha-adducin gene results from alternate use of the 5' splice donor site for exon 10, while another results in a truncated protein following insertion of 34 bp comprising exon 15, followed by a premature stop codon. This alternate spliced form of alpha-adducin is predicted to result in an altered carboxyl terminus that would eliminate a protein kinase and calmodulin binding site. Seven nucleotide substitutions and 4 insertion/deletions were also identified. The 5' region of the human alpha-adducin gene contains one Sp1 site, two AP2 sites, and two CAAT boxes. No TATA box was apparent, consistent with features of a housekeeping gene. We have mapped another cDNA within the first intron of the human alpha-adducin gene, suggesting overlapping genes in this 4p16.3 genomic region.

Alternative Splicing↗
PubMed1994

Murine alpha-L-iduronidase: cDNA isolation and expression.

As an initial step toward the generation of a murine model for mucopolysaccharidosis type I, we have identified and characterized a full-length murine alpha-L-iduronidase cDNA. Expression of the murine cDNA in COS-1 cells results in the production of alpha-L-iduronidase enzyme activity at a level 20-fold higher than that of the endogenous gene. The murine cDNA shows strong homology with the coding region of both the human and the canine homologs with 78 and 75% nucleotide sequence identity, respectively. In contrast to the coding region, significant diversity of sequence exists for the 5' and 3' untranslated regions between the murine and both the human and the canine sequence. The 3' UTR of the murine transcript is 1193 bp in length, as compared to the human (100 bp) and canine (139 bp), and contains a CA dinucleotide repeat not seen in either the human or the canine genes. A portion of the murine iduronidase coding sequence overlaps with sequence reported for the 3' UTR of the murine SAT-1 cDNA. The sequence overlap involves the proposed exon II of murine iduronidase and covers 141 bp of sequence with the transcripts generated in opposite orientation. We report here the characterization of murine alpha-L-iduronidase cDNA and its relationship to SAT-1.

Animals↗
PubMed1994

The murine homologues of the Huntington disease gene (Hdh) and the alpha-adducin gene (Add1) map to mouse chromosome 5 within a region of conserved synteny with human chromosome 4p16.3.

Huntington disease (HD) is a severe autosomal dominant neurodegenerative disorder associated with a novel gene (IT15). Recently, we reported the cloning of Hdh, the murine homologue of IT15. Here, using an interspecific backcross, we have mapped both Hdh and the mouse homologue of human alpha-adducin (Add1), a membrane-associated cytoskeletal protein gene. Both of these genes map in the same position on mouse chromosome 5 in a region associated with ancestral chromosomal rearrangements and show no recombination with D5H4S43, D5H4S115, and D5H4S62, the murine homologues of D4S43, D4S115, and D4S62, respectively. Further mapping studies of humans, mice, and other mammalian species should reveal the nature of the rearrangements affecting this chromosomal segment during mammalian evolution.

Animals↗
PubMed1994

Sequence of the murine Huntington disease gene: evidence for conservation, alternate splicing and polymorphism in a triplet (CCG) repeat [corrected].

Huntington disease (HD) is associated with significant expansion of a CAG trinucleotide repeat within a novel gene. However, no clues to the function of this gene were apparent by sequence alignment to other proteins. We have therefore sought to identify the mouse gene (hd) as a first step in the development of an animal model for HD to provide insights into the molecular pathogenesis of this disease. Here, we report the sequencing of cDNA clones spanning 9,992 nucleotides encoding the murine HD homologue (hd), which exhibits 90% peptide sequence identity, including conservation of the CAG and adjacent CCG repeats. In addition, we show that the CCG is polymorphic in the mouse. Sequence analysis provides strong evidence that the first in frame methionine 5' to the CAG repeat, is the translational start site, for both the mouse and human transcript. As in human, the gene appears expressed in the mouse as 2 large transcripts. We observe evidence for alternate splicing of the hd gene in mouse tissues which would predict two protein products differing by 480 amino acid residues with a molecular mass difference of approximately 54 kilodaltons.

Alternative Splicing↗
PubMed1993

Differential 3' polyadenylation of the Huntington disease gene results in two mRNA species with variable tissue expression.

Recently a novel gene containing a CAG trinucleotide repeat that is expanded on HD chromosomes has been identified(1). This gene was shown to detect a single transcript of 10-11 kb by RNA hybridization. We have however, previously identified three cDNAs which are part of the same gene that have been shown to detect two distinct transcripts of 10 kb and one that is significantly larger(2,3). These different mRNA species could be due to use of alternate transcription start sites, alternate splicing or selection of different polyadenylation sites. We have identified cDNA clones spanning the HD gene including two (HD12 and HD14) that share identical protein coding sequences but differ in size and sequence of their 3' untranslated region. HD14 has 3,360 base pairs of additional sequence distal to the previously published 3' end (1). RNA hybridization has revealed that the larger 13.7 kb fragment is the predominant transcript in human brain. cDNA fragments unique to HD14 detected only the larger transcript. Sequence analysis identified two different putative polyadenylation sequences at position 10,326 and 13,645 of the HD14 cDNA. These findings indicate that the two observed mRNA species originate from a single gene and that differential polyadenylation leads to transcripts of different size. The relative increased abundance of the larger transcript in human brain may provide some insights into the mechanism by which a widely expressed gene may exert tissue specific effects.

Base Sequence↗