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Biomedical subjects

A K Maiti

Publications and source records attributed to A K Maiti.

At least 19 recordsLinked to original sources
PubMed2001

Poly purine.pyrimidine sequences upstream of the beta-galactosidase gene affect gene expression in Saccharomyces cerevisiae.

BACKGROUND: Poly purine.pyrimidine sequences have the potential to adopt intramolecular triplex structures and are overrepresented upstream of genes in eukaryotes. These sequences may regulate gene expression by modulating the interaction of transcription factors with DNA sequences upstream of genes. RESULTS: A poly purine.pyrimidine sequence with the potential to adopt an intramolecular triplex DNA structure was designed. The sequence was inserted within a nucleosome positioned upstream of the beta-galactosidase gene in yeast, Saccharomyces cerevisiae, between the cycl promoter and gal 10 Upstream Activating Sequences (UASg). Upon derepression with galactose, beta-galactosidase gene expression is reduced 12-fold in cells carrying single copy poly purine.pyrimidine sequences. This reduction in expression is correlated with reduced transcription. Furthermore, we show that plasmids carrying a poly purine.pyrimidine sequence are not specifically lost from yeast cells. CONCLUSION: We propose that a poly purine.pyrimidine sequence upstream of a gene affects transcription. Plasmids carrying this sequence are not specifically lost from cells and thus no additional effort is needed for the replication of these sequences in eukaryotic cells.

Journal Article↗
PubMed2001

Isolation, in silico characterization and chromosomal localization of a group of cDNAs from ciliated epithelial cells after in vitro ciliogenesis.

BACKGROUND: Immotile cilia syndrome (ICS) or primary ciliary dyskinesia (PCD) is an autosomal recessive disorder in humans in which the beating of cilia and sperm flagella is impaired. Ciliated epithelial cell linings are present in many tissues. To understand ciliary assembly and motility, it is important to isolate those genes involved in the process. RESULTS: Total RNA was isolated from cultured ciliated nasal epithelial cells after in vitro ciliogenesis and expressed sequenced tags (ESTs) were generated. The functions and locations of 63 of these ESTs were derived by BLAST from two public databases. These ESTs are grouped into various classes. One group has high homology not only with the mitochondrial genome but also with one or more chromosomal DNAs, suggesting that very similar genes, or genes with very similar domains, are expressed from both mitochondrial and nuclear DNA. A second class comprises genes with complete homology with part of a known gene, suggesting that they are the same genes. A third group has partial homology with domains of known genes. A fourth group, constituting 33% of the ESTs characterized, has no significant homology with any gene or EST in the database. CONCLUSIONS: We have shown that sufficient information about the location of ESTs could be derived electronically from the recently completed human genome sequences. This strategy of EST localization should be significantly useful for mapping and identification of new genes in the forthcoming human genome sequences with the vast number of ESTs in the dbEST database.

Cells, Cultured↗
PubMed2001

Axonemal beta heavy chain dynein DNAH9: cDNA sequence, genomic structure, and investigation of its role in primary ciliary dyskinesia.

Dyneins are multisubunit protein complexes that couple ATPase activity with conformational changes. They are involved in the cytoplasmatic movement of organelles (cytoplasmic dyneins) and the bending of cilia and flagella (axonemal dyneins). Here we present the first complete cDNA and genomic sequences of a human axonemal dynein beta heavy chain gene, DNAH9, which maps to 17p12. The 14-kb-long cDNA is divided into 69 exons spread over 390 kb. The cDNA sequence of DNAH9 was determined using a combination of methods including 5' rapid amplification of cDNA ends, RT-PCR, and cDNA library screening. RT-PCR using nasal epithelium and testis RNA revealed several alternatively spliced transcripts. The genomic structure was determined using three overlapping BACs sequenced by the Whitehead Institute/MIT Center for Genome Research. The predicted protein, of 4486 amino acids, is highly homologous to sea urchin axonemal beta heavy chain dyneins (67% identity). It consists of an N-terminal stem and a globular C-terminus containing the four P-loops that constitute the motor domain. Lack of proper ciliary and flagellar movement characterizes primary ciliary dyskinesia (PCD), a genetically heterogeneous autosomal recessive disorder with respiratory tract infections, bronchiectasis, male subfertility, and, in 50% of cases, situs inversus (Kartagener syndrome, KS). Dyneins are excellent candidate genes for PCD and KS because in over 50% of cases the ultrastructural defects of cilia are related to the dynein complex. Genotype analysis was performed in 31 PCD families with two or more affected siblings using a highly informative dinucleotide polymorphism located in intron 26 of DNAH9. Two families with concordant inheritance of DNAH9 alleles in affected individuals were observed. A mutation search was performed in these two "candidate families," but only polymorphic variants were found. In the absence of pathogenic mutations, the DNAH9 gene has been excluded as being responsible for autosomal recessive PCD in these families.

Adenosine Triphosphate↗
PubMed2000

Identification, tissue specific expression, and chromosomal localisation of several human dynein heavy chain genes.

Sliding between adjacent microtubules within the axonema gives rise to the motility of cilia and flagella. The driving force is produced by dynein complexes which are mainly composed of the axonemal dynein heavy chains. We used cells of human respiratory epithelium after in vitro ciliogenesis to clone cDNA fragments of nine dynein heavy chain genes, one of which had never been identified before. Dynein heavy chains are highly conserved from protozoa to human and the evolutionary ancestry of these dynein heavy chain cDNA fragments was deduced by phylogenetic analysis. These dynein heavy chain cDNAs are highly transcribed in human tissues containing axonema such as trachea, testis and brain, but not in adult heart or placenta. PAC clones containing dynein heavy chains were obtained and used to determine by FISH their chromosomal position in the human genome. They were mapped to 2p12-p11, 2q33, 3p21.2-p21.1, 13q14, 16p12 and 17p12. The chromosomal assignment of these dynein heavy chain genes which was confirmed by GeneBridge 4 radiation hybrid screening, will be extremely useful for linkage analysis efforts in patients with primary ciliary dyskinesia (PCD).

Amino Acid Sequence↗
PubMed2000

No deleterious mutations in the FOXJ1 (alias HFH-4) gene in patients with primary ciliary dyskinesia (PCD).

The transcription factor FOXJ1 (alias HFH-4 or FKHL13) of the winged-helix/forkhead family is expressed in cells with cilia or flagella, and seems to be involved in the regulation of axonemal structural proteins. The knockout mouse Foxj1(-/-) shows abnormalities of organ situs, consistent with random determination of left-right asymmetry, and a complete absence of cilia. The human FOXJ1 gene which maps to chromosome 17q, is thus an excellent candidate gene for Kartagener Syndrome (KS), a subphenotype of Primary Ciliary Dyskinesia (PCD), characterized by bronchiectasis, chronic sinusitis and situs inversus. We have collected samples from 61 PCD families, in 31 of which there are at least two affected individuals. Two families with complete aciliogenesis, and six families, in which the affected members have microsatellite alleles concordant for a locus on distal chromosome 17q, were screened for mutations in the two exons and intron-exon junctions of the FOXJ1 gene. No sequence abnormalities were observed in the DNAs of the affected individuals of the selected families. These results demonstrate that the FOXJ1 gene is not responsible for the PCD/KS phenotype in the families examined.

Alleles↗
PubMed1997

Polypurine/polypyrimidine sequences as cis-acting transcriptional regulators.

Genome sequence information has generated increasing evidence for the claim that repetitive DNA sequences present within and around genes could play a important role in the regulation of gene expression. Polypurine/polypyrimidine sequences [poly(Pu/Py)] have been observed in the vicinity of promoters and within the transcribed regions of many genes. To understand whether such sequences influence the level of gene expression, we constructed several prokaryotic and eukaryotic expression vectors incorporating poly(Pu/Py) repeats both within and upstream of a reporter gene, lacZ (encoding beta-galactosidase), and studied its expression in vivo. We find that, in contrast to the situation in Escherichia coli, the presence of poly(Pu/Py) sequences within the gene does not significantly inhibit gene expression in mammalian cells. On the other hand, the presence of such sequences upstream of lacZ leads to a several-fold reduction of gene expression in mammalian cells. Similar down-regulation was observed when a structural cassette containing poly(Pu/Py) sequences upstream of lacZ was integrated into yeast chromosome V. Sequence analysis of the nine totally sequenced yeast chromosomes shows that a large number of such sequences occur upstream of ORFs. On the basis of our experimental results and DNA sequence analysis, we propose that these sequences can function as cis-acting transcriptional regulators.

Animals↗
PubMed1994

Vagal tone and the physiological regulation of emotion.

On the basis of current knowledge of neuroanatomy and our previous research with cardiac vagal tone, we have proposed the vagal circuit of emotion regulation. The vagal circuit of emotion regulation incorporates lateral brain function with the regulation of the peripheral autonomic nervous system in the expression of emotion. The vagus and the vagal circuit do not function independently of other neurophysiological and neuroendocrine systems. Research on brain activity (see Dawson, in this volume; Fox, in this volume) and research on adrenocortical activity (see Stansbury & Gunnar, in this volume) demonstrate that EEG and cortisol are related to emotion states and to individual differences similar to those that we have investigated. The vagal circuit emphasizes not only the vagus but also the lateralization of specific brain structures in emotion regulation. The emphasis of the vagal circuit on right-brain-stem structures stimulates several testable hypotheses regarding the function of specific structures in the right brain in emotion regulation. These speculations are consistent with other reports (see Dawson, in this volume; Fox, in this volume) describing asymmetrical EEG activity during expressed emotions. Moreover, the vagal circuit does not exist independently of the brain structures and peptide systems regulating cortisol (see Stansbury & Gunnar, in this volume). Areas in the brain stem regulating vagal activity are also sensitive to the peptides that regulate cortisol (e.g., vasopressin and corticotropin-releasing hormone). In this essay, we have provided information regarding the relation between vagal tone and emotion regulation. A review of research indicates that baseline levels of cardiac vagal tone and vagal tone reactivity abilities are associated with behavioral measures of reactivity, the expression of emotion, and self-regulation skills. Thus, we propose that cardiac vagal tone can serve as an index of emotion regulation. Historically, the vagus and other components of the parasympathetic nervous system have not been incorporated in theories of emotion. Recent developments in methodology have enabled us to define and accurately quantify cardiac vagal tone. Theories relating the parasympathetic nervous system to the expression and regulation of emotion are now being tested in several laboratories.

Affect↗
PubMed1992

The mcm2 mutation of yeast affects replication, rather than segregation or amplification of the two micron plasmid.

We have studied the maintenance of the endogenous two micron (2 mu) plasmid in a strain of yeast carrying the nuclear mutation mcm2. This mutation, earlier shown to affect the maintenance of yeast minichromosomes in an ARS-dependent manner, also affected the copy number of the 2 mu plasmid. The effect was more pronounced at 35 degrees C leading to the elimination of the plasmid from the cells cultured at this temperature. The mutant cells could be efficiently cured of the circle by transformation with 2 mu ORI-carrying hybrid vectors, an observation consistent with the low copy number of the endogenous plasmid. A chromosomal revertant of this mutant for another ARS(ARS1) was found also to confer stability on the 2 mu ORI-carrying minichromosomes and had elevated levels of the endogenous plasmid. The mutation neither affected the segregation nor the amplification process mediated by site-specific recombination at FRT sites requiring the FLP gene-encoded protein action. ARS131C, an ARS that was unaffected in the mutant at 25 degrees C, could elevate the copy number of a 2 mu hybrid vector in the mutant cells. In view of these results, some aspects of segregation and copy number control of the endogeneous plasmid have been discussed. We propose that the mutation impairs the 2 mu ORI function, leading to its loss.

Cell Division↗
PubMed1989

Influences of vestibulo-cerebellum on kindling in the cat.

The development of amygdaloid kindling was assessed under conditions of pharmacological depression of the nodular areas of vestibulocerebellum and also following vestibular stimulation in chronically prepared cats. The results demonstrated that a single intra-nodular micro-injection of procaine hydrochlorides could significantly facilitate such epileptogenesis for at least several days. The number of kindling trials required to reach the first generalized convulsions was significantly increased by natural vestibular stimulation in comparison with control kindled animals. The intensity of fit, development of amygdaloid seizures and the convulsions were reduced markedly within a week by pre-conditioning the kindled animals with daily vestibular stimulation for 15-30 min. In addition, analysis of the behaviour of sleep-wake cycle indicated a significant increase in total sleep time and in the percentage of rapid eye movement (REM) sleep. These findings suggest that the natural rotational vestibular stimulation may result in a durable modification of brain function through development of enduring focal sensitization of catecholamine-mediated inhibitory mechanisms, reflecting the tonic inhibitory influences of the vestibulo-cerebellum in regulating the development and attenuation of epileptic states.

Animals↗