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Biomedical subjects

R Weber

Publications and source records attributed to R Weber.

At least 397 records · Page 22Linked to original sources
PubMed1981

Xenopus laevis serum albumins are encoded in two closely related genes.

cDNA clones containing sequences complementary to Xenopus laevis albumin mRNA have been identified in a collection of cDNA clones made from poly(A)+ RNA prepared from male Xenopus laevis liver. Although all the albumin cDNA clones crosshybridise, restriction enzyme and heteroduplex analysis show that there are 2 closely related albumin mRNA sequences. The 2 albumin mRNAs are only mismatched by 8% but could be isolated by positive selection using stringent hybridization conditions. Oocytes injected with the 2 purified mRNAs, secreted either the 68,000 or 74,000 dalton albumin into the culture medium showing that the 2 albumins of X. laevis serum are encoded in the 2 closely related mRNAs. Measurements of the abundance of albumin mRNA show that the 2 albumin mRNAs together account for about 9% of total poly(A)+ RNA in male Xenopus laevis liver but the mRNA coding for the 74,000 dalton mRNA is about twice as abundant as that coding for the 68,000 dalton mRNA.

Animals↗
PubMed1981

Quantitation of DNase I sensitivity in Xenopus chromatin containing active and inactive globin, albumin and vitellogenin genes.

The disappearance of defined restriction fragments of the beta 1-globin, an albumin and the A1 vitellogenin gene was quantitated after DNase I digestion and expressed by a sensitivity factor defined by a mathematical model. Analysis of naked DNA showed that the gene fragments have similar but not identical sensitivity factors. DNase I digestion of chromatin revealed for the same gene fragments sensitivity factors differing over a much wilder range. This is correlated to the activity of the genes analyzed: the beta 1-globin gene fragment is more sensitive to DNase I in chromatin of erythrocytes compared to hepatocytes whereas the albumin gene fragment is more sensitive to DNase I in chromatin of hepatocytes. The A1 vitellogenin gene has the same DNase I sensitivity in both cell types. Comparing the DNase I sensitivity of the three genes in their inactive state we suggest that different chromatin conformations may exist for inactive genes.

Albumins↗
PubMed1981

Estrogen induces tissue specific changes in the chromatin conformation of the vitellogenin genes in Xenopus.

Nuclei from male Xenopus liver were digested extensively with DNase I and the residual amount of the four vitellogenin genes measured by hybridization with a moderate excess of vitellogenin cDNA. The saturation value was about twofold lower in chromatin isolated from liver cells of estrogen treated than from untreated males or from erythrocytes. Analyzing the disappearance of several defined restriction fragments specific for the A1 and A2 vitellogenin genes, after limited digestion with DNase I, suggested that the entire A1 and A2 vitellogenin genes are about twofold more sensitive to DNase I in chromatin of hepatocytes isolated from estrogen treated than from untreated males. Using the same assay no change in the DNase I sensitivity of the two vitellogenin genes in erythrocyte chromatin was observed. Analysis of the beta 1-globin and an albumin gene demonstrated that the DNase I sensitivity of these genes in both cell types is not altered by estrogen. All these data indicate that estrogen stimulation results in an increased DNase I sensitivity specific for the vitellogenin genes in hepatocytes.

Animals↗
PubMed1981

Vitellogenesis and the vitellogenin gene family.

Vitellogenin is synthesized under estrogen control in the liver, extensively modified, transported to the ovary, and there processed to the yolk proteins lipovitellin and phosvitin. In the frog Xenopus laevis there are at least four distinct but related vitellogenin genes. The two genes A1 and A2 have a 95 percent sequence homology in their messenger RNA coding regions, and contain 33 introns that interrupt the coding region (exons) at homologous positions. Sequences and lengths of analogous introns differ, and many introns contain repetitive DNA elements. The introns in these two genes that have apparently arisen by duplication have diverged extensively by events that include deletions, insertions, and probably duplications. Rapid evolutionary change involving rearrangements and the presence of repeated DNA suggests that the bulk of the sequences within introns may not have any specific function.

Animals↗
PubMed1980

Comparative analysis of the structural organization of two closely related vitellogenin genes in X. laevis.

The structural organization of the two closely related vitellogenin genes A1 and A2 has been determined and compared by electron microscopy. In both genes the mRNA-coding sequence of 6 kb is interrupted 33 times, leading to a total gene length of 21 kb for gene A1 and 16 kb for gene A2. Thus both genes have a mean exon length of 0.175 kb, while the mean intron length is 0.45 kb in gene A1 and 0.31 kb in gene A2. Because the introns interrupt the structural sequence at homologous positions in genes A1 and A2, we suggest that these two genes are the products of a duplication of an ancestral gene which has an intron-exon arrangement similar to that of the extant genes. Since the duplication event, the sequence and length of the analogous introns have changed rapidly, whereas homologous exons have diverged to an extent of only 5% of their sequences. The results suggest different mechanisms of evolution for exons and introns. While the exons evolved primarily by point mutations, such mutations, as well as deletion, insertion and duplication events, were important in the evolution of the introns.

Animals↗
PubMed1980

Identification, organization and processing intermediates of the putative precursors of Xenopus vitellogenin messenger RNA.

To understand the mechanism of estrogen-induced activation of the vitellogenin genes in the liver of Xenopus, it is essential to characterize the transcriptional products of these genes. In this paper we describe large nuclear RNAs containing vitellogenin mRNA sequences as revealed by hybridization of cloned vitellogenin cDNAs to nuclear RNA separated on agarose gels. Putative vitellogenin mRNA precursors, which are recovered as poly(A)-containing RNA, have been identified for the four known vitellogenin mRNAs. From electron microscopic analysis of R loops, prepared between enriched mRNA precursors and cDNA specific for the A1 vitellogenin mRNA, we conclude that the precursor molecules contain sequences complementary to vitellogenin mRNA which are interrupted by additional RNA segments probably representing transcribed introns. Within the 3.7 kb of the 3' end of the A1 vitellogenin mRNA we have discovered seven large and at least five small transcribed introns. Some of the R loops have been found to contain only a few transcribed introns, and we assume that they represent processing intermediates. Comparison of these putative intermediates suggests that the splicing order of different introns does not follow a single pathway.

Animals↗
PubMed1980

Isolation and translation in vitro of four related vitellogenin mRNAs of estrogen-stimulated Xenopus laevis.

Cloning of vitellogenin cDNA of Xenopus laevis revealed that vitellogenin is encoded in a small family of genes representing two distantly related main groups A and B, each comprising two more closely related subgroups A1, A2, and B1, B2 respectively. To characterize the proteins derived from these genes we have isolated the corresponding mRNAs by hybridizing, under stringent conditions, cytoplasmic poly(a)-containing RNA from the liver of estrogen-stimulated Xenopus to filter-bound cDNA clones containing sequences specific for all four vitellogenin genes. Hybridization of the isolated mRNAs with nick-translated cDNA clones revealed that contamination of the mRNAs by those of the other main group was less than 0.1%. Melting curves of the hybrids prepared with the isolated mRNAs and cDNA clones specific for the four vitellogenin genes showed that the isolated vitellogenin mRNAs are also specific for the four subgroups. Analysis of R loops formed between isolated mRNAs and cDNA clones representing the corresponding subgroup further indicated about 10% cross-contamination between the more closely related mRNAs. In a reticulocyte lysate each of the four mRNAs coded for a 200 000-Mr protein immunoprecipitable by monospecific vitellogenin antibody. From these results we conclude that the four different mRNAs A1, A2, B1 and B2, which all can be isolated efficiently, code for vitellogenin and are expressed simultaneously in response to estrogen stimulation.

Animals↗
PubMed1980

Four different vitellogenin proteins of Xenopus identified by translation in vitro.

Kinetic analysis of vitellogenin mRNA translation in a cell-free reticulocyte lysate translation system revealed that a serine-rich sequence, most probably containing the phosvitin molecule, is located toward the end of the translational product and therefore resides near to the carboxy terminus of the vitellogenin molecule. Translation of the four different vitellogenin mRNAs in vitro and cleavage of the translational products with cyanogen bromide revealed that vitellogenin consists of four different polypeptides, each containing a serine-rich sequence toward its carboxy terminus.

Animals↗
PubMed1980

A consumeristic trend in industrial therapy.

The importance in the development of the industrial therapy program is not very significant in itself. What is important, is that rehabilitation professionals are staying abreast of the needs of the consumers. With so many of the rehabilitation services being offered in the public sector, this sensitivity is often lost. Until the funding for these services is directly correlated with consumer satisfaction, this tendency will be likely to continue in many settings. Until that time comes, the responsiveness of the public agency to the consumer's needs will depend, to a great extent, on the integrity of the professionals within that agency.

Occupational Therapy↗
PubMed1979

Enrichment and characterization of the DNA coding for vitellogenin in Xenopus laevis.

Purified vitellogenin mRNA of Xenopus laevis was incubated with mechanically sheared DNA in high concentrations of formamide and the resulting R-loops (i.e. RNA . DNA hybrid fragments) separated from the bulk DNA by caesium chloride buoyant density centrifugation. Hybridization with 125I-labeled vitellogenin mRNA revealed a 15--30-fold enrichment of the DNA coding for vitellogenin. Restriction analysis of the R-loop-enriched DNA demonstrated that all known endonuclease HindIII fragments coding for vitellogenin of unfractionated Xenopus DNA were also present in the enriched material, including the specific fragments for the oligo(A)-containing segment of the RNA. Comparison of these restriction data with the structure found in cloned vitellogenin cDNA, indicates the presence of at least one intervening sequence in the genomic DNA coding for vitellogenin.

Animals↗
PubMed1979

Vitellogenin in Xenopus laevis is encoded in a small family of genes.

Vitellogenin, the yolk protein precursor, is produced in X. laevis liver from a 6.3 kilobase (kb) mRNA. Sequences of this mRNA have been transcribed into cDNA and cloned in E. coli. Some properties of 21 of these cloned DNAs, ranging in size from 1 to 3.7 kb, have been reported by Wahli et al. (1978b). This paper reports restriction endonuclease mapping, cross hybridization, heteroduplex mapping in the electron microscope and heteroduplex melting experiments with these DNAs. We conclude that the cloned DNAs fall into two main groups of sequences which differ from each other in approximately 20% of their nucleotides. Each main group contains two subgroups which differ from each other by about 5% sequence divergence. By hybridizing cloned DNAs with restricted genomic DNA, we showed that sequences corresponding to all four sequence groups are present in a single animal. Furthermore, we have obtained tentative evidence for the presence of large intervening sequences in genomic vitellogenin DNA. Analysis of R loop molecules demonstrated that all four sequences are present in the vitellogenin mRNA population purified from individual animals. While some alternate explanations are not entirely excluded, we suggest that vitellogenin is encoded by a small family of related genes in Xenopus.

Animals↗
PubMed1978

Medicaid-funded private psychiatric care in New York City. The role of foreign-trained physicians.

Data were obtained from the tax records and the Professional Registry maintained by the New York City Department of Health as well as from the Biographical Directory of the American Psychiatric Association to determine which psychiatrists were providing care under the Medicaid Program and how they compare with the pool of psychiatric practitioners in New York City. The data reveal that psychiatrists educated in foreign medical schools provide disproportionately more care to Medicaid recipients than would be anticipated from their numbers, and are a majority of those who received more than +30,000 in payments in 1976. Furthermore, these psychiatrists account for 80 per cent of those delivering care at the two largest "shared health facilities," commonly referred to as "Medicaid mills." These findings indicate that although the Title XIX Program has facilitated the access of the poor to the private psychiatric sector, in New York City their access is biased toward treatment by foreign-educated psychiatrists.

Foreign Medical Graduates↗