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D Hentzen

Publications and source records attributed to D Hentzen.

17 recordsLinked to original sources
PubMed1997

Diabetes update.

Explore the source record for details and available documents.

Blood Glucose Self-Monitoring↗
PubMed1996

Growth and differentiation of C2 myogenic cells are dependent on serum response factor.

In order to study to what extent and at which stage serum response factor (SRF) is indispensable for myogenesis, we stably transfected C2 myogenic cells with, successively, a glucocorticoid receptor expression vector and a construct allowing for the expression of an SRF antisense RNA under the direction of the mouse mammary tumor virus long terminal repeat. In the clones obtained, SRF synthesis is reversibly down-regulated by induction of SRF antisense RNA expression by dexamethasone, whose effect is antagonized by the anti-hormone RU486. Two kinds of proliferation and differentiation patterns have been obtained in the resulting clones. Some clones with a high level of constitutive SRF antisense RNA expression are unable to differentiate into myotubes; their growth can be blocked by further induction of SRF antisense RNA expression by dexamethasone. Other clones are able to differentiate and are able to synthesize SRF, MyoD, myogenin, and myosin heavy chain at confluency. When SRF antisense RNA expression is induced in proliferating myoblasts by dexamethasone treatment, cell growth is blocked and cyclin A concentration drops. When SRF antisense RNA synthesis is induced in arrested confluent myoblasts cultured in a differentiation medium, cell fusion is blocked and synthesis of not only SRF but also MyoD, myogenin, and myosin heavy chain is inhibited. Our results show, therefore, that SRF synthesis is indispensable for both myoblast proliferation and myogenic differentiation.

Animals↗
PubMed1995

Induction of interferon-beta gene expression by dexamethasone in murine L929 cells.

Glucocorticoids bind to their receptors and trigger the transcriptional activation or repression of target genes by binding to DNA sequences, the glucocorticoid responsive element (GRE). The murine interferon-beta (Mu-IFN beta) gene in L929 cells can be induced by dexamethasone to give both transcription and translation products specific to murine IFN beta. The 3'-noncoding region of the Mu-IFN beta gene was found to contain a GRE very similar to the consensus GRE sequence involved in glucocorticoid-regulated genes. Gel retardation assays showed that the oligonucleotide corresponding to that GRE competed with the MMTV GRE oligonucleotide for glucocorticoid receptor binding and was supershifted by human antiglucocorticoid receptor antibodies. Transiently transfected murine cells (L929) with the GRE-IFN beta 3' sequence inserted upstream of the thymidine kinase promoter and the chloramphenicol acetyl transferase gene treated with dexamethasone with or without the antiglucocorticoid RU486 and their chloramphenicol acetyl transferase activity assayed, show that this GRE is efficient. We conclude that the Mu-IFN beta gene in L929 murine cells can be induced by dexamethasone, and that the hormone effect may be mediated by the 3'-GRE sequence.

Animals↗
PubMed1992

Site specific screening for point mutations in ornithine transcarbamylase deficiency.

Ornithine transcarbamylase (OTC) deficiency is a frequent X linked disorder of the urea cycle which is responsible for lethal neonatal hyperammonaemia in males and for various clinical symptoms in heterozygous females. In order to improve the efficiency of our screening for mutant genotypes, we focused on molecular domains of functional or structural importance in the OTC gene, namely the carbamyl phosphate binding domain (encoded by the third exon) and the MspI restriction sites (CCGG) of the coding sequence (located in exons 2 and 7 respectively), as they contain mutation hot spots (CpG doublets). Using this procedure, we were able to identify three new mutant genotypes in OTC deficient children including one nonsense mutation (E 87 K, G 50 ter, G 162 R). Since genetic counselling for OTC deficiency is frequently difficult, molecular screening directed towards specific sites of the coding sequence could allow rapid detection of mutant genotypes and help solve diagnostic problems, especially when carrier status cannot be clarified easily.

Amino Acid Metabolism, Inborn Errors↗
PubMed1991

Fatal hyperammonemia resulting from a C-to-T mutation at a MspI site of the ornithine transcarbamylase gene.

Ornithine transcarbamylase (OTC) deficiency is the most common inborn error of the urea cycle in humans and is responsible for lethal neonatal hyperammonemia in males. Partial OTC deficiency also occurs in females and can be responsible for life-threatening hyperammonemic comas in heterozygotes. The cosegregation of the trait with a 5.8-kb abnormal MspI fragment in an affected family led us to hypothesize that this unexpected migration pattern was related to the mutation event in this particular family. Using polymerase chain reaction amplification of the specific mRNA derived from a post-mortem biopsy of the liver, we found that the MspI site located in the seventh exon of the gene was abolished and we finally identified a C-to-T transition at codon 225 of the cDNA, changing a proline to a leucine in the protein. Subsequent digestion of amplified exon 7 using the restriction enzyme MspI allowed direct screening for the mutant genotype during the next pregnancy. The present study supports the view that direct detection of the mutant genotype using either Southern blotting or digestion of amplified exons of the gene can contribute to genetic counselling in noninformative families. Finally, since MspI digestions are routinely performed for restriction fragment length polymorphism-based family studies in OTC deficiency, we suggest that the possible presence of the 5.8-kb abnormal fragment should be investigated on Southern blots of affected individuals.

Amino Acid Metabolism, Inborn Errors↗
PubMed1990

Carrier detection in a partially dominant X-linked disease: ornithine transcarbamylase deficiency.

Ornithine transcarbamylase (OTC) deficiency is an X-linked disease responsible for lethal neonatal hyperammonemia in males. Partial OTC deficiency also occurs in females and can be responsible for life-threatening hyperammonemic comas in heterozygotes (15%). Increased orotic acid excretion occurs in both symptomatic and asymptomatic carriers, especially under protein loading tests. The disease is therefore partially dominant with neonatal lethality in the hemizygous male; the fraction of new mutations has previously been estimated to be low in males (point estimation = 0, upper bound of the confidence interval = 0.16) and 57% in females. Genetic counseling in this disease is difficult because it is not clear whether a negative protein loading test rules out carrier status. In an attempt to determine how reliable the test is for carrier detection, we investigated ten obligate carriers for orotic acid excretion; considering all data available, we concluded that the test is rarely negative in obligate carriers (8%). Consequently, a negative test in a mother decreases the minimum risk of being a carrier from 84% a priori to 30% if she had an affected son and from 43% a priori to 5% if she had a heterozygous daughter. Finally, the diagnosis of a new mutation in the germ cells of the maternal grandfather in one particular family could be ascertained by extensive DNA analysis.

Bayes Theorem↗
PubMed1989

Increase in ribosomal protein S6 phosphorylation is due to v-erbB-transforming activity and not to v-erbA mitogenic activity in avian erythroblastosis virus-infected chicken embryo fibroblasts.

Avian erythroblastosis virus (AEV-ES4), a transforming avian retrovirus, transforms chicken embryo fibroblasts (CEFs) in culture and induces the maintenance of ribosomal protein S6 phosphorylation in the absence of serum. This effect is less pronounced after AEV-ES4 transformation than after transformation by Rous sarcoma virus (PR-RSV A). However, our results indicate that the two viruses induce an activation of the same S6 phosphokinase, as evidenced by the identity of S6 phosphopeptides and phosphoaminoacids in the two cases. Moreover this activation is performed through a protein kinase C-independent pathway. Expression of the v-erbA oncogene alone, which enhances the growth potential of CEFs, is not able to maintain S6 phosphorylation either in the absence of serum or in the presence of low serum concentration (0.5%). Expression of the v-erbB oncogene alone is responsible for all these AEV-ES4-induced effects. Furthermore, the maintenance of S6 phosphorylation in the absence of serum might be correlated with the degree of transformation of AEV-ES4-infected CEFs. These results show that S6 phosphorylation is one of the biochemical mechanisms deregulated by v-erbB expression and is involved in the transformation process.

Alpharetrovirus↗
PubMed1987

The chicken c-erbA proto-oncogene is preferentially expressed in erythrocytic cells during late stages of differentiation.

We analyzed the expression of the c-erbA proto-oncogene in different tissues of chicken embryos. c-erbA transcripts were found at low levels in the lung, kidney, liver, and heart and in high amounts in embryonic blood cells. Nuclease mapping assays proved that these transcripts were true c-erbA transcripts. In situ hybridization on fractionated embryonic blood cells showed that c-erbA transcripts were predominantly found in erythroblasts, particularly during the final step of differentiation. Life span analysis of c-erbA mRNAs revealed their relative instability, demonstrating that the high level of c-erbA transcripts in embryonic erythroblasts was not the result of passive accumulation. These results suggest that the c-erbA genes play some role in erythrocyte differentiation.

Animals↗
PubMed1981

Differential usage of iso-accepting tRNASer species in silk glands of Bombyx mori.

The rapid development of the silk glands of Bombyx mori during the last larval instar shows two phases. During the first 4 days, in both the middle and posterior parts of the silk glands, the ribosomal machinery is assembled and the synthesis of housekeeping proteins starts. During the second phase (the last 4 days), the middle part of the gland synthesis approximately 45 mg of the silk protein sericin (31% serine) and the posterior part of the gland synthesizes approximately 130 mg of the silk protein fibroin (46% glycine, 29% alanine and 12% serine). Silk fibroin and sericin are detectable by the second day and represent 80 and 50% respectively of the total proteins produced at day 8 (refs 1--4). It is known that the tRNA population of the posterior part of the gland is quantitatively adapted to fibroin codon frequency during this period but little is known about the situation in the middle part except for the observation that it contains more tRNASer than does the posterior part. We show here that the two parts contain, and presumably use, different iso-accepting species of tRNASer, the middle part using tRNASer1, which recognizes AGU and AGC codons, and the posterior part using tRNASer2 which recognizes UCA. We also suggest that this differential adaptation of the tRNASer species is under transcriptional control as the two species are accumulated at different rates, but degraded at the same rate.

Animals↗
PubMed1976

Structural studies on RNA from Bombyx mori L. I. Nucleoside composition of enriched tRNA species from the posterior silkgland purified by coutercurrent distribution.

A large scale fractionation of tRNA from the posterior silkgland of the silkworm Bombyx mori L. by countercurrent distribution is described. One single 1,500 transfer distribution carried out with Phosphate buffer-Fromamide-Isopropanol (PFI) solvent system yields highly enriched isoaccepting species with increasing mobility order: tRNA1Gly, tRNA1-2Ala, tRNATyr, tRNA2Gly, tRNA1Ser and tRNA2Ser with 75%, 70%, 90%, 60%, 60%, and 90% purities respectively. Nucleosides fingerprint analysis of each iso-tRNA species confirms the anticodon structures previously suggested for tRNA2Ala (IGC), tRNA2bGly (U-CC) (U-CC) and tRNA2bSer (IGA). Twenty two minor nucleosides, three of them with unknown structure, have been detected. They are: m5C in tRNA1Gly, m1I in all tRNAAla species, polar A and U called X in tRNATyr, polar U derivative in tRNAGly2, mt6A in tRNASer1 and i6A tRNA2Ser. Both tRNASer species have m3C and ac7C. We do not detect Q, Y and thiol derivatives. The elution characteristics of silkgland tRNA species may be expressed in a semilogarithmic diagram where log K (K is the partition coefficient) is related to the base ratio A/Y) and the coding properties. The distribution pattern of silkgland tRNAs has been compared with that of Yeast and Rat liver tRNAs fractionated by countercurrent distribution with the PFI and PMB (Potassium phosphate buffer, 2-methoxy ethanol, 2-butoxy ethanol) solvent systems.

Animals↗
PubMed1976

Analysis of the transfer RNA population of mouse mammary glands infected with a latent mammary tumor virus.

Mammary gland transfer RNA's (tRNA'S) of CEH mice infected with mammary tumor virus were analyzed in the preneoplastic state and compared to tRNAs of virus-free C3Hf mice and another uninfected strain, C57BL/6, which is completely resistant to cancer. This quantitative study was based on the ability of each tRNA to fix its corresponding amino acid. The amount of each of the 17 tRNA's tested was identical for the three mammary glands. In addition, tRNA populations during lactation correlated with the amino acids incorporated into the lactoproteins synthesized, which indicates adapation of the tRNA's to protein biosynthesis. Qualitative chromatographic studies on reverse phase capillary columns Type 5 of 10 aminoacyl-tRNA's did not reveal any difference in the isoacceptor elution profiles. This shows that no new isoaccepting tRNA is associated with the mammary tumor virus at that stage, and that no viral modification of a host tRNA has occurred.

Amino Acids↗