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R Taneja

Publications and source records attributed to R Taneja.

36 records · Page 2Linked to original sources
PubMed1996

The expression pattern of the mouse receptor tyrosine kinase gene MDK1 is conserved through evolution and requires Hoxa-2 for rhombomere-specific expression in mouse embryos.

Segmentation of the hindbrain has been conserved throughout the vertebrate species and results in the transient formation of rhombomeres, which are lineage-restricted compartments. Studies on the molecular mechanisms underlying the segmentation process have revealed that rhombomeric boundaries coincide with the expression limits of several evolutionary conserved genes such as the zinc-finger transcription factor Krox-20 and homeobox genes which are expressed in a specific spatial and temporal order and have been shown to be important regulators of segmental identity. In addition to Krox-20 and Hox genes, several members of the Eph subfamily of receptor protein tyrosine kinase (RTK) genes are also expressed in a segment-restricted manner in the hindbrain, suggesting that these receptors may act in concert with Hox genes to establish regional identity. In the cascade of regulatory interactions leading to segmental identity, Krox-20 appears to act "upstream" of Hox genes, but the identity of the "downstream" effectors has not yet been identified. We report here the isolation of the zebrafish orthologue of the mouse RTK gene MDK1 which belongs to the Eph receptor subfamily and show that the major expression domains of the mouse and the zebrafish genes have been conserved through evolution. Since the coincident spatial and temporal expression of Hoxa-2 and MDK1 in the mouse hindbrain suggested a possible regulatory link between them, we analyzed the expression of the MDK1 in Hoxa-2 null mutant embryos. A selective lack of MDK1 expression in rhombomere 3 of Hoxa-2 mutant hindbrains together with an overall altered expression pattern in the other rhombomeres was observed, thus demonstrating that MDK1 lies downstream of Hoxa-2 in the morphogenetic signaling cascade.

Amino Acid Sequence↗
PubMed1996

Cell-type and promoter-context dependent retinoic acid receptor (RAR) redundancies for RAR beta 2 and Hoxa-1 activation in F9 and P19 cells can be artefactually generated by gene knockouts.

By using RAR type (alpha, beta, or gamma)-specific synthetic retinoids and a pan-retinoic X receptor (RXR)-specific ligand, we have investigated the contribution of RARs and RXRs in the activation of RA target genes and the differentiation of embryonal carcinoma cells. We demonstrate cell-type- and promoter context-dependent functional redundancies that differ between the three RAR types for mediating the induction of RARbeta2 and Hoxa-1 in wild-type, RARgamma-/- and RARalpha-/- F9 cells and in P19 cells. The extent of redundancy between RARs is further modulated by the synergistic activation of RXRs with a pan-RXR agonist. We also demonstrate that the expression of RARbeta2 is auto-inducible in RARgamma-/- but not in wild-type F9 cells, indicating that the functional redundancies observed between RARs in gene disruption studies can be artefactually generated. Thus, even though all three RARs can functionally substitute each other for inducing the expression of RA target genes and cell differentiation, one RAR can cell-specifically override the activity of the other RARs. Interestingly, only RARgamma can mediate the retinoic acid-induced differentiation of wild-type F9 cells, whereas the differentiation of P19 cells can be mediated by either RARalpha or RARgamma.

Cell Differentiation↗
PubMed1995

Reexpression of retinoic acid receptor (RAR) gamma or overexpression of RAR alpha or RAR beta in RAR gamma-null F9 cells reveals a partial functional redundancy between the three RAR types.

Disruption of retinoic acid receptor (RAR) gamma in F9 embryonal carcinoma cells leads to aberrent differentiation and reduced activation of expression of several all-trans-retinoic acid (RA)-induced genes. We have analyzed the expression of several additional RA-responsive genes in RAR alpha- and RAR gamma-null F9 cells. The RA-induced activation of Cdx1, Gap43, Stra4, and Stra6 was specifically impaired in RAR gamma-null cells, supporting the idea that each RAR may regulate distinct subsets of target genes. To further investigate the role of RAR gamma in F9 cell differentiation, "rescue" cell lines reexpressing RAR gamma 2 or overexpressing either RAR alpha 1 or RAR beta 2 were established in RAR gamma-null cells. Reexpression of RAR gamma or overexpression of RAR alpha restored both target-gene activation and the differentiation potential. In contrast, over-expression of RAR beta only poorly restored differentiation, although it could replace RAR gamma for the activation of target genes. Functional redundancy between the various RARs is discussed.

Animals↗
PubMed1995

Tuberculin screening of trauma admissions at a university hospital. A preventive strategy.

OBJECTIVE: To determine the prevalence of tuberculosis (TB) infection in our trauma service population, namely, those patients who had positive Mantoux (purified protein derivative [PPD] [tuberculin]) tests. DESIGN: Prospective study. SETTING: Trauma service at a university hospital in Newark, NJ. PATIENTS AND METHODS: During a 9-month period, 110 admitted trauma patients underwent screening for TB. Of these patients, 20 had undergone recent PPD tests in the last 6 months, of which nine were positive. The remaining 90 patients underwent PPD and delayed-type hypersensitivity skin tests (anergy panel); five patients were unavailable for follow-up. The patients also answered questions regarding human immunodeficiency virus status, risk factors for TB infection, and clinical symptoms. RESULTS: The mean age of the study group was 34 years (age range, 13 to 69 years). Eighty-four percent of these patients were males who belonged to the high-risk socioeconomic, racial, and ethnic groups (poor, non-white). The tests for 15 patients (17%) were newly discovered to be positive for PPD. Eleven percent of the patients with negative PPD tests were anergic, thus raising the percentage of patients with positive PPD tests to 20%. The human immunodeficiency virus status was known in only 41% of the total patients. All patients with positive PPD tests had a chest x-ray film performed; of these patients, positive findings for TB were determined for one patient. Another patient had evidence of abdominal TB at laparotomy. All patients with positive PPD tests were given appointments in the pulmonary clinic for follow-up, and only three of 15 patients kept their appointments. CONCLUSIONS: Patients who were admitted to the trauma service were predominantly young males from high-risk groups with a high incidence of TB infection. Their admission to the trauma service was a unique opportunity for screening and implementing existing preventive programs.

Adult↗
PubMed1995

Synergistic activation of retinoic acid (RA)-responsive genes and induction of embryonal carcinoma cell differentiation by an RA receptor alpha (RAR alpha)-, RAR beta-, or RAR gamma-selective ligand in combination with a retinoid X receptor-specific ligand.

Retinoic acid receptor (RAR)-retinoid X receptor (RXR) heterodimers bind to cognate response elements in vitro more efficiently than do RAR or RXR homodimers, and both RAR and RXR partners have been shown to activate various promoters in transiently transfected cells. We have now investigated whether ligand-dependent activation of both heterodimeric partners is involved in induced expression of endogenous RA-responsive genes and in P19 and F9 cell differentiation. On their own, low concentrations of retinoids selective for either RAR alpha, RAR beta, or RAR gamma did not induce or very inefficiently induced the expression of several RA target genes or triggered differentiation. An RXR-specific synthetic retinoid was similarly inefficient at any concentration. In contrast, at the same concentrations, various combinations of RAR (RAR alpha, RAR beta, or RAR gamma) and RXR selective retinoids resulted in synergistic induction of all retinoic acid (RA) target genes examined, as well as in cell differentiation. However, the magnitude of this synergistic activation varied depending on both the RAR-RXR combination and the promoter context of the responsive genes. Promiscuous activation of the three RARs, or concomitant activation of RAR alpha and RAR gamma, at selective retinoid concentrations also resulted in induction of gene expression and cell differentiation. Taken together, our results are consistent with the conclusion that the RAR and RXR partners of RAR-RXR heterodimers can synergistically activate transcription of RA-responsive genes and can induce differentiation of P19 and F9 cells. Our results also indicate that there is a significant degree of functional redundancy between the three RAR types which, however, varies with the nature of the RA target genes.

Animals↗
PubMed1995

Targeted disruption of retinoic acid receptor alpha (RAR alpha) and RAR gamma results in receptor-specific alterations in retinoic acid-mediated differentiation and retinoic acid metabolism.

F9 embryonic teratocarcinoma stem cells differentiate into an epithelial cell type called extraembryonic endoderm when treated with retinoic acid (RA), a derivative of retinol (vitamin A). This differentiation is presumably mediated through the actions of retinoid receptors, the RARs and RXRs. To delineate the functions of each of the different retinoid receptors in this model system, we have generated F9 cell lines in which both copies of either the RAR alpha gene or the RAR gamma gene are disrupted by homologous recombination. The absence of RAR alpha is associated with a reduction in the RA-induced expression of both the CRABP-II and Hoxb-1 (formerly 2.9) genes. The absence of RAR gamma is associated with a loss of the RA-inducible expression of the Hoxa-1 (formerly Hox-1.6), Hoxa-3 (formerly Hox-1.5), laminin B1, collagen IV (alpha 1), GATA-4, and BMP-2 genes. Furthermore, the loss of RAR gamma is associated with a reduction in the metabolism of all-trans-RA to more polar derivatives, while the loss of RAR alpha is associated with an increase in metabolism of RA relative to wild-type F9 cells. Thus, each of these RARs exhibits some specificity with respect to the regulation of differentiation-specific gene expression. These results provide an explanation for the expression of multiple RAR types within one cell type and suggest that each RAR has specific functions.

Animals↗
PubMed1995

Repair of a massive ventral hernia in a morbidly obese patient.

Aggressive perioperative management, with progressive preoperative pneumoperitoneum, is a worthy method of repairing massive ventral hernias with associated loss of domain in morbidly obese patients. The authors present a case and its successful outcome.

Adult↗
PubMed1993

Differential transcription of multiple copies of a silk worm gene encoding tRNA(Gly1).

Ten different tRNA(Gly1) genes from the silk worm, Bombyx mori, have been cloned and characterized. These genes were transcribed in vitro in homologous nuclear extracts from the posterior silk gland (PSG) or nuclear extracts derived from the middle silk gland or ovarian tissues. Although the transcription levels were much higher in the PSG nuclear extracts, the transcriptional efficiency of the individual genes followed a similar pattern in all the extracts. Based on the levels of in vitro transcription, the ten tRNA(Gly1) genes could be divided into three groups, viz., those which were transcribed at very high levels (e.g., clone pR8), high to medium levels (e.g., pBmi1, pBmp1, pBmh1, pBmt1) and low to barely detectable levels (e.g., pBms1, pBmj1 and pBmk1). The coding sequences of all these tRNA genes being identical, the differential transcription suggested that the flanking sequences modulate their transcriptional efficiency. The presence of positive and negative regulatory elements in the 5' flanking regions of these genes was confirmed by transcription competition experiments. A positive element was present in the immediate upstream A+T-rich sequences in all the genes, but no consensus sequences correlating to the transcriptional status could be generated. The presence of negative elements on the other hand was indicated only in some of the genes and therefore may have a role in the differential transcription of these tRNA(Gly1) genes in vivo.

Animals↗
PubMed1993

Loss of retinoic acid receptor gamma function in F9 cells by gene disruption results in aberrant Hoxa-1 expression and differentiation upon retinoic acid treatment.

Retinoic acid (RA) signal transduction is believed to be mediated through several high-affinity nuclear receptors [RA receptors (RARs) and retinoid X receptors], which are members of the steroid/thyroid/vitamin D superfamily and function as transcription factors. Why multiple RARs exist and what gene targets are regulated by each of the three receptors remain compelling questions in developmental biology. Through targeted disruption of both RAR gamma alleles, we have identified several differentiation-specific genes that are regulated either directly or indirectly by RAR gamma in F9 embryonal carcinoma cells. These include genes encoding Hoxa-1 (Hox-1.6) and the extracellular matrix proteins laminin B1 and collagen type IV (alpha 1), all of which are RA inducible in wild-type F9 embryonal carcinoma cells but are not significantly induced in the RAR gamma-/- lines. In contrast, transcripts encoding Hoxb-1 (Hox-2.9) and cellular RA binding protein II (CRABPII) are activated by RA for a longer period of time in the RAR gamma-/- lines compared to the wild-type F9 line. Not all RA-responsive genes are aberrantly expressed; Rex-1, RAR beta, and SPARC transcripts are regulated in the RAR gamma-/- lines as they are in F9 wild-type cells. Our results support the idea that each RAR may regulate different subsets of RA-responsive genes, which may explain, in part, the complex regulation of developmental processes by retinoids.

Animals↗
PubMed1992

Regulation of glycine tRNA gene expression in the posterior silk glands of the silkworm Bombyx mori.

The glycine tRNA genes in silkworm Bombyx mori contain two regulatory regions upstream of the transcription start site as identified by direct transcription of 5' deletion mutants, transcription competition, gel mobility shift assays, and footprinting. A positive regulatory region is present in the immediate 5' flanking sequences of the four tRNA 1Gly clones studied. This region is essential for cell-free transcription in homologous extracts. A negative regulatory region is present farther upstream, and transcription competition experiments indicate its presence in three of the four clones examined.

Animals↗
PubMed1983

Effect of fatty acid supplementation on the lipid composition of Mycobacterium smegmatis ATCC 607, grown at 27 degrees and 37 degrees C.

Mycobacterium smegmatis ATCC 607 was grown at 27 and 37 degrees C, with and without exogenous unsaturated fatty acids, viz. elaidic, oleic and palmitoleic acids, added to the growth medium. The total lipid content of M. smegmatis ATCC 607 was lower at 27 degrees C, and with added oleic acid, when compared with the controls, but higher in presence of palmitoleic acid. At 37 degrees C no significant differences were noted in the total lipid content. In general, the total lipid content was lower with all of the fatty acid supplementations at both 27 and 37 degrees C. The phosphatidylethanolamine content was slightly higher at 27 degrees C in the presence of elaidic or palmitoleic acid, but was markedly lower with oleic acid supplementation at 37 degrees C. The cardiolipin content was lower in the presence of any of the fatty acids at 27 degrees C, and higher in the medium supplemented with elaidic or oleic acid at 37 degrees C. The unsaturated to saturated fatty acids ratio was higher with palmitoleic acid supplementation at 27 degrees C, but remained unchanged in cells grown at 37 degrees C. The modifications in mycobacterial lipids are a reflection of the organism's ability to adapt to changing growth conditions.

Culture Media↗
PubMed1982

Lipid composition and virulence of Mycobacterium tuberculosis H37Rv.

The total lipids increased with decrease in total phospholipids in Mycobacterium tuberculosis H37Rv grown at 30 degrees as compared to 37 degrees. Oleic and elaidic acid supplemented to the growth medium resulted in a higher total lipid and phospholipid content, but the content was lower in cells grown in the presence of palmitoleic acid. Cellular content of mannophosphoinositides decreased, whereas that of phosphatidylethanolamine and cardiolipin increased at the lower temperature. A decrease in mannophosphoinositides and an increase in cardiolipin were noted with all fatty acid supplements; however, phosphatidylethanolamine behaved differently. The unsaturated to saturated fatty acids ratio increased at low temperature with oleic and elaidic acid supplements, but it decreased with palmitoleic acid. Cells from media supplemented with palmitoleic acid were found to be most virulent to guinea-pigs. Possible correlation of altered lipid composition and virulence of M. tuberculosis H37Rv has been discussed.

Animals↗
PubMed1981

Phospholipid metabolism in Mycobacterium smegmatis ATCC 607 grown at 37 degrees and 27 C degrees C.

The rate of synthesis and degradation of phospholipids in Mycobacterium smegmatis ATCC 607, grown at 27 degrees C and 37 degrees C was studied incorporation of 32P into phospholipids and chase of radioactivity of the pulse-labelled phospholipids. A relatively low rate of synthesis and degradation of phospholipids in cells growth at 27 degrees C was observed as compared to those grown at 37 degrees C. Phosphatidylethanolamine (PE) had the maximum turnover at 37 degrees C. However, at 27 degrees C, cardiolipin (CL) showed a turnover rate higher than PE. Phosphatidylinositol mannosides (PIMs) were metabolically more active at 37 degrees C than at 27 degrees C. The differences in metabolic activity of the phospholipids at the two temperatures have been discussed.

Cardiolipins↗
PubMed1979

Effect of growth temperature on the lipid composition of Mycobacterium smegmatis ATCC 607.

The total lipid content of Mycobacterium smegmatis ATCC 607 was the same whether it was grown at 27 or 37 degrees C. The total phospholipid content, however, increased significantly at 27 degrees C. Phosphatidylethanolamine increased most markedly with a simultaneous decrease in phosphatidylinositol mannosides. Among individual phosphatidylinositol mannosides, tri- and tetra-acylated dimannophosphoinositides and tetra-acylated hexamannophosphoinositides all decreased at the lower growth temperature. Triacylglycerols and monoacylglycerols increased at the lower temperature but diacylglycerols were unaffected. Unsaturated fatty acids of total phospholipids increased as the temperature was lowered.

Lipid Metabolism↗