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M Schartl

Publications and source records attributed to M Schartl.

At least 127 records · Page 7Linked to original sources
PubMed1991

On the stability of dispensable constituents of the eukaryotic genome: stability of coding sequences versus truly hypervariable sequences in a clonal vertebrate, the amazon molly, Poecilia formosa.

In clonal unisexual vertebrates, the genes specifying the males become dispensable. To study the fate of such genes the gynogenetic all-female fish Poecilia formosa was treated with androgens. Phenotypic males were obtained that exhibited the complete set of male characteristics of closely related gonochoristic species, including body proportions, pigmentation, the extremely complex insemination apparatus of poeciliid fish, sexual behavior, and spermatogenesis. The apparent stability of such genic structures, including those involved in androgen regulation, is contrasted by high instability of noncoding sequences. Frequent mutations, their clonal transmission, and at least two truly hypervariable loci leading to individual differences between these otherwise clonal organisms were detected by DNA fingerprinting. These observations substantiate the concept that also in "ameiotic" vertebrates certain compartments of the genome are more prone to mutational alterations than others.

Journal Article↗
PubMed1991

Transient expression of foreign DNA during embryonic and larval development of the medaka fish (Oryzias latipes).

Species of small fish are becoming useful tools for studies on vertebrate development. We have investigated the developing embryo of the Japanese medaka for its application as a transient expression system for the in vivo analysis of gene regulation and function. The temporal and spatial expression patterns of bacterial chloramphenicol acetyltransferase and galactosidase reporter genes injected in supercoiled plasmid form into the cytoplasm of one cell of the two-cell stage embryo was promoter-specific. The transient expression was found to be mosaic within the tissue and organs reflecting the unequal distribution of extrachromosomal foreign DNA and the intensive cell mixing movements that occur in fish embryogenesis. The expression data are consistent with data on DNA fate. Foreign DNA persisted during embryogenesis and was still detectable in some 3- and 9-month-old adult fish; it was found in high molecular weight form as well as in circular plasmid conformations. The DNA was replicated during early and late embryogenesis. Our data indicate that the developing medaka embryo is a powerful in vivo assay system for studies of gene regulation and function.

Animals↗
PubMed1991

Analysis of an esterase linked to a locus involved in the regulation of the melanoma oncogene and isolation of polymorphic marker sequences in Xiphophorus.

Melanoma formation in Xiphophorus hybrids is mediated by a growth factor receptor tyrosine kinase oncogene encoded by the Tu locus. In the wild-type parental fish no tumors occur due to the activity of a locus that regulates the activity of the melanoma oncogene. Molecular identification of this regulatory locus (R) requires a precise physical map of the chromosomal region. Therefore we studied esterase isozymes in Xiphophorus, two of which have been previously reported to be linked to locus R. We confirm that ES1 is a distant marker for R (approx. 30cM), and contrary to earlier studies, we show that this isozyme is present in all species of the genus and at similar activity levels in all organs tested. ES4, which has also been reported to be linked to R, was found to be a misclassification of liver ES1. In an attempt to identify markers that bridge the large distance between ES1 and R, we have generated DNA probes which are highly polymorphic. They will be useful in finding landmarks on a physical map of the R-containing chromosomal region.

Animals↗
PubMed1991

Conservation of structure and expression of the c-yes and fyn genes in lower vertebrates.

The src-gene family in mammals and birds consists of 9 closely related protein tyrosine kinases. We have cloned the c-yes and fyn homologues of the src-family from the teleost fish Xiphophorus helleri. Both genes show a high degree of sequence conservation and exhibit all structural motifs diagnostic for functional src-like protein tyrosine kinases. Sequence comparisons revealed three domains (exon 2, exons 3-6, exons 7-12) which evolve at different rates. Both genes exhibit an identical expression pattern, with preferential expression in neural tissues. No transcripts of c-yes were found in liver which is contrary to the situation in higher vertebrates. In malignant melanoma, elevated levels of c-yes and fyn were detected indicating a possible function during secondary steps of tumor progression for src-related tyrosine kinases.

Amino Acid Sequence↗
PubMed1991

Transcriptional activation of the melanoma inducing Xmrk oncogene in Xiphophorus.

The melanoma inducing locus of Xiphophorus encodes a tumorigenic version of a novel putative receptor tyrosine kinase (Xmrk). To elucidate the mechanism of oncogenic activation of Xmrk, we compared the structure and expression of two oncogenic loci with the corresponding proto-oncogene. Only minor structural alterations were found to be specific for the oncogenic Xmrk genes. Marked overexpression of the oncogene transcripts in melanoma, which are approximately 1 kb shorter than the proto-oncogene transcript, correlates with the malignancy of the tumors. The tumor transcripts are derived from an alternative transcription start site that is used only in the oncogenic loci. Thus, oncogenic activation of the melanoma inducing Xmrk gene appears primarily to be due to novel transcriptional control and overexpression.

Animals↗
PubMed1990

Transient expression directed by homologous and heterologous promoter and enhancer sequences in fish cells.

In order to construct fish specific expression vectors for studies on gene regulation in vitro and in vivo a variety of heterologous enhancers and promoters from mammals and from viruses of higher vertebrate cells were tested for expression of the bacterial chloramphenicol acetyl transferase reporter gene in three teleost fish cell lines. Several viral enhancers were found to be constitutively active at high levels. The human metallothionein promoter showed inducible expression in the presence of heavy metal ions. A fish sequence was isolated that can be used as a homologous constitutively active promoter for expression of foreign genes. Using the human growth hormone gene with an active promoter in fish cells for transient expression insufficient splicing and lack of translation were observed, pointing to limitations in the use of heterologous genes in gene transfer experiments. On the contrary, some heterologous promoters and enhancers functioned in fish cells as well as in their cell type of origin, indicating that corresponding transcription factors are sufficiently conserved between fish and human over a period of 900 million years of independent evolution.

Animals↗
PubMed1990

Oncofetal antigen in Xiphophorus detected by monoclonal antibodies directed against melanoma-associated antigens.

Monoclonal antibodies (MAbs) directed against Xiphophorus melanoma cells were developed and tested by indirect immunofluorescence and immunoperoxidase staining for reactivity with a panel of 15 allogeneic tissues and 12 allogeneic cell lines. The reactivity of such MAbs was restricted to melanoma cells from tumor biopsies and melanoma-derived cell lines. In addition, all embryonic cells of all histiotypes from developmental stages later than mid-organogenesis and from corresponding short term in vitro cultures reacted with these MAbs. In contrast, normal tissues and organs from adult fish displayed no reactivity, thus implying that the melanoma-associated antigens detected by the MAbs described are oncofetal antigens.

Animals↗
PubMed1990

Myocardial contrast echocardiography: cardiovascular effects of the contrast medium SHU 454 in dogs.

SHU 454 (Schering AG, Berlin, Federal Republic of Germany) is a new contrast agent that releases microbubbles with a median diameter of 3 microns into the circulation. During echocardiography, it permits visualization of myocardial blood flow (MBF) when given by intracoronary or aortic root injections. Its hemodynamic effects were investigated in anesthetized dogs with a view to application in humans. Cardiac effects were studied after intracoronary injections of 1 mL of SHU 454 (100 mg/mL). Twenty seconds after injection, MBF increased 35% and coronary vascular resistance decreased accordingly. The increase in MBF was not seen when the coronary bed was maximally dilated with intravenous dipyridamole. Peripheral effects were evaluated after 5 mL of SHU 454 (200 mg/mL) was injected into the aortic root, which gave the same myocardial echo contrast. Aortic pressure decreased 5%, and heart rate and dP/dt increased. To evaluate the effects of hypertonicity, SHU 454 was compared with five radiocontrast media and glucose. Its effects on MBF were similar to those of radiologic contrast media on an equal volume basis. Only 1 mL of intracoronary SHU 454, however, was required for myocardial contrast enhancement. The results suggest that visualization of the myocardium using SHU 454 or similar compounds for contrast echocardiography is a viable prospect.

Animals↗
PubMed1990

Homology of melanoma-inducing loci in the genus Xiphophorus.

Several species of the genus Xiphophorus are polymorphic for specific pigment patterns. Some of these give rise to malignant melanoma following the appropriate crossings. For one of these pattern loci from the playfish Xiphophorus maculatus the melanoma-inducing gene has been cloned and found to encode a novel receptor tyrosine kinase, designated Xmrk. Using molecular probes from this gene in Southern blot analyses on single fish DNA preparations from 600 specimens of different populations of various species of the genus Xiphophorus and their hybrids, either with or without melanoma-predisposing pattern, it was shown that all individuals contain the Xmrk gene as a proto-oncogene. It is located on the sex chromosome. All fish that carry a melanoma-predisposing locus which has been identified by Mendelian genetics contain an additional copy of Xmrk, closely linked to a specific melanophore pattern locus on the sex chromosome. The melanoma-inducing loci of the different species and populations are homologous. The additional copy of Xmrk obviously arose by a gene-duplication event, thereby acquiring the oncogenic potential. The homology of the melanoma-inducing loci points to a similar mechanism of tumor suppression in all feral fish populations of the different species of the genus Xiphophorus.

Animals↗
PubMed1990

Synaptophysin: a substrate for the protein tyrosine kinase pp60c-src in intact synaptic vesicles.

Expression of pp60c-src, the first well defined proto-oncogene product, is developmentally regulated and tissue-specific, with neuronal tissues displaying high amounts of the c-src encoded pp60c-src kinase activity. In the central nervous system pp60c-src is preferentially expressed in regions characterized by a high content of grey matter and elevated density of nerve terminals. In this study we show for the first time a direct interaction between pp60c-src and synaptophysin as a physiological target protein in neurons by demonstrating that endogenous pp60c-src is able to phosphorylate synaptophysin (p38). p38 is a major constituent of the synaptic vesicle membrane protein and is thought to play a key role in the exocytosis of small synaptic vesicles and possibly small clear vesicles in neuroendocrine cells.

Animals↗
PubMed1989

Novel putative receptor tyrosine kinase encoded by the melanoma-inducing Tu locus in Xiphophorus.

Malignant melanoma in Xiphophorus fish hybrids is caused by the activity of a dominant oncogene Tu. By combining genetic and molecular approaches, we have isolated the melanoma oncogene. We show that its level of expression correlates with the degree of malignancy of the tumour. The corresponding proto-oncogene is developmentally regulated. The Tu gene codes for a novel receptor tyrosine kinase which is closely related to the receptor for epidermal growth factor.

Amino Acid Sequence↗
PubMed1989

Evolution of the neuron-specific alternative splicing product of the c-src proto-oncogene.

The observation of a slower migrating form of pp60c-src in neural tissue of chicken and mouse has recently been shown to be due to an alternative transcript form of the c-src gene (Martinez et al.: Science 237:411-415, 1987; Levy et al.: Mol Cell Biol 7:4142-4145, 1987). An insertion of 18 basepairs between exons 3 and 4, presumed to be due to alternative splicing of a mini-exon, gives rise to six amino acid residues not found in the non-neuronal (termed fibroblastic) form of pp60c-src. We have addressed the question of the evolutionary origin of the c-src neuronal insert and its functional significance regarding neural-specific expression of the c-src gene. To this end we have investigated whether the c-src gene of a lower vertebrate (the teleost fish Xiphophorus) gives rise to a neural-specific transcript in an analogous manner. We could show that the fish c-src gene does encode for a "fibroblastic" and a "neuronal" form of transcript and that the neuronal transcript does indeed arise by way of alternative splicing of a mini-exon. The mini-exon is also 18 basepairs long and we could demonstrate directly that this exon lies within the intron separating exons 3 and 4. For comparative purposes we have examined whether the fish c-yes gene, the member of the src gene family most closely related to c-src, also encodes a neural tissue-specific transcript. No evidence for a second transcript form in brain was obtained.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1989

Structure and expression of the murine retinoblastoma gene and characterization of its encoded protein.

We have isolated a cDNA clone of the murine homologue of the human retinoblastoma (Rb) susceptibility gene. DNA sequence analysis reveals a high degree of conservation with the human Rb sequence, both in the coding and in the noncoding regions. The predicted amino acid sequence of the mouse Rb protein shows 91% identity to that of the human protein. Both proteins were found to contain a peptide sequence reminiscent of a leucine-repeat motif ("leucine-zipper") that is also found in the myc, fos, and jun oncogenes. Synthetic peptide antiserum directed against a portion of the mouse Rb protein detects three proteins of 104-110 kDa in cells that were transiently transfected with a mouse Rb gene expression construct. In the mouse embryo the expression of Rb mRNA was ubiquitous, with maximal expression being observed around 13 days of gestation. In the embryo, the highest level of expression was observed in liver and brain. In contrast, the Rb gene was found to be expressed at a very low level in adult mouse liver with high levels being found in lung, thymus, and spleen. A shorter Rb transcript was detected in mouse testes.

Amino Acid Sequence↗
PubMed1989

Preferential expression of a pp60c-src related protein tyrosine kinase activity in nerve cells of the early metazoan Hydra (Coelenterates).

It has been suggested that the proto-oncogene c-src plays a functional role in developing neurons, and in the mature nerve cells of higher vertebrates. The coelenterate Hydra represents the most primitive known organism possessing nerve cells. With Southern blot hybridizations we have demonstrated src-related sequences in Hydra. Antisera specific for the c-src gene product (pp60c-src) of birds and mammals precipitate a protein from Hydra cell extracts with a tyrosine-specific protein kinase activity. Studies of tissues and cells fractionated from a temperature sensitive mutant of Hydra which is depleted of interstitial (including nerve) cells at the non-permissive temperature, have indicated the src-like kinase of Hydra to be preferentially expressed in nerve cells. The high conservation of structural features and of the expression pattern indicates a basic function for pp60c-src in neurons.

Animals↗
PubMed1989

Dose-related effects of intracoronary application of nisoldipine on central and peripheral circulatory parameters.

In a randomized study central and peripheral circulatory parameters were determined in 12 anaesthetized mongrel dogs before and after intracoronary injection of nisoldipine and placebo. Administration of 0.2 to 0.8 micrograms/kg nisolpine was followed by a 46% to 62% decrease in coronary vascular resistance and a 109% to 141% increase in myocardial blood flow lasting 10 min. There was no significant change in myocardial contractility or peripheral circulatory parameters. An increase in dosage to 1.6 micrograms/kg did not cause a further increase in myocardial blood flow or decrease in coronary vascular resistance. However, there was a significant decrease in total peripheral resistance of up to 32% and a 36% increase in heart rate attributable to counter-regulation lasting 3 to 5 min. At this dosage level a significant decrease in myocardial contractility and an increase in left ventricular end-diastolic pressure are to be expected. This implies a major dissociation between coronary vascular effects and changes in parameters of myocardial performance and peripheral resistance after intracoronary administration of nisoldipine, an effect which is dose-related. Injection of 0.4 to 0.8 micrograms/kg would seem to be the optimal dosage range for intracoronary administration of nisoldipine producing maximum coronary dilatation without myocardial depression.

Animals↗