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Biomedical subjects

M Schartl

Publications and source records attributed to M Schartl.

At least 73 records · Page 4Linked to original sources
PubMed1998

Does dobutamine stress echocardiography induce damage during viability diagnosis of patients with chronic regional dysfunction after myocardial infarction?

Experimental hibernating-model investigations of animals have shown that myocardial necrosis can be induced by longer-term intracoronary dobutamine infusion. This study was designed to determine whether myocardial infarction could be ascertained in patients with chronic regional wall motion abnormalities and greater than 75% stenosis in the supplying coronary artery through dobutamine stress echocardiography. Twenty patients with coronary artery disease and regional resting wall motion abnormalities were examined with a standard dobutamine protocol (5 to 50 microg/kg/min). Exclusion criteria were an acute coronary syndrome, severe heart failure, and severe hypertension. Creatine kinase (CK, CKMB), myoglobin, and troponine-I were measured before and at each of the first 7 hours after beginning of infusion. Fourteen of these 20 patients exhibited viable myocardium. The serum markers CK, CKMB, myoglobin, and troponin-I demonstrated no increase beyond the reference range, suggesting that with this protocol, no myocardial necrosis was induced.

Blood Pressure↗
PubMed1998

The macromelanophore locus and the melanoma oncogene Xmrk are separate genetic entities in the genome of Xiphophorus.

Fish of the genus Xiphophorus are polymorphic for black pigmentation patterns. Certain intra- or interspecific hybrids exhibit enhanced expression of these patterns, leading in many cases to malignant melanoma. Because no recombination was ever observed between the pattern information and the genetic predisposition to develop melanoma after hybridization, a "tumor gene" (Tu) was postulated that encodes both phenotypes. A dominant oncogene, ONC-Xmrk, was then found to be necessary and sufficient for the transforming function of Tu. Here we present molecular evidence that ONC-Xmrk and the pigment pattern information are encoded by separate, although intimately linked loci. No ONC-Xmrk gene was present in the 15 Xiphophorus strains investigated which exhibit no black pigmentation pattern. Five different patterns from Xiphophorus maculatus, X. evelynae, X. milleri, X. cortezi, and X. montezumae were associated with ONC-Xmrk and were melanomagenic, while fish of X. helleri, X. variatus, X. nezahualcoyotl, and X. montezumae with five other patterns had no ONC-Xmrk and consequently did not produce hybrid melanoma. These data provide evidence that ONC-Xmrk is sufficient for tumorigenesis in Xiphophorus hybrids, and that a separate, pigment pattern-encoding locus is closely linked to it.

Animals↗
PubMed1998

Dispensable and indispensable genes in an ameiotic fish, the Amazon molly Poecilia formosa.

All-female vertebrates are excellent model systems for studying many evolutionary problems. One of these is the Amazon molly. In this review, three aspects of its biology are discussed: (1) An important question is how dispensable genes, such as all male coding genes, evolve in this species. A number of studies found that most of these genes remain remarkably stable and functional. (2) The gynogenetic Amazon mollies have to live in sympatry with males of a gonochoristic species, because sperm are needed to trigger embryogenesis. Yet, Amazon mollies cannot replace their sexual competitors, because this would lead to their own extinction. Studies on the behavior of Amazon mollies and their sperm-donor species indicate that a number of behavior patterns stabilize the mating system by providing Amazon mollies with the copulations they need to reproduce. (3) The age of Amazon mollies has been estimated to be approximately 100,000 years. This is older than predicted by some theoretical models. In Amazon mollies two ways to occasionally incorporate fresh genetic material have evolved. One way is to add one complete set of paternal chromosomes, which, in nature, leads to stable triploid lineages. The second way is the incorporation of minute, centromere-containing microchromosomes. The evolutionary impact of these phenomena, however, is not resolved so far and needs further study.

Animals↗
PubMed1998

Localization of a CDKN2 gene in linkage group V of Xiphophorus fishes defines it as a candidate for the DIFF tumor suppressor.

The Xiphophorus hybrid melanoma model represents one of the earliest reported cases of genetically regulated tumor susceptibility. Melanoma formation in Xiphophorus hybrids may be explained by the inheritance of two genes: a sex-linked oncogene, Xmrk, and a putative tumor suppressor locus, termed DIFF, located in Linkage Group V (LG V). Several genetic mapping procedures were used to produce a new Xiphophorus LG V map with 20 loci. All markers, particularly a recently cloned Xiphophorus CDKN2 gene family member, called CDKN2X, were tested for associations of genotype with degree of macromelanophore pigment pattern modification and susceptibility to melanoma formation in backcross hybrids of seven genetic types, involving 1,110 fish and three pigment patterns. Highly significant associations of CDKN2X genotypes with such phenotypic effects suggests that this gene is a strong candidate for the classically defined DIFF tumor suppressor gene. Because published results have documented the involvement of the CDKN2A (p16, MTS1, and INK4A) tumor suppressor gene in human melanoma formation, the possibility of CDKN2 genes acting as tumor suppressors in both man and Xiphophorus is likely.

Animals↗
PubMed1998

Efficient gene transfer into Xiphophorus muscle and melanoma by injection of supercoiled plasmid DNA.

Muscle and melanoma tissue of fish in the genus Xiphophorus were examined for their ability to take up and express foreign DNA. Supercoiled plasmid DNA containing a firefly luciferase reporter gene with expression driven by the cytomegalovirus enhancer and thymidylate kinase promoter was directly injected into the muscle or melanoma of individual Xiphophorus. Expression levels gradually increased to a maximum at 6 days after injection in both tissues, and this level was maintained for at least 10 days after injection. In both muscle and melanoma, there was a clear relationship between dose injected and reporter gene activity, with maximal expression at a dose of 20 microg of plasmid injected. At higher doses expression levels declined, suggesting the possibility that the uptake mechanism can be inhibited by high concentrations of DNA. Histochemical localization using a beta-galactosidase construct revealed high expression of the enzyme in isolated muscle fibers. The activity of a second coinjected reporter gene, sea pansy (Renilla reniformis) luciferase, was highly correlated with the activity of the firefly luciferase reporter gene in both tissues (R2 >.940), suggesting that the majority of variation between samples results from variation in overall DNA uptake between individuals. When firefly luciferase activity is expressed as a function of activity of the coinjected reporter, the variation between samples is greatly reduced. As a result, small differences in activity between constructs can be detected. This demonstrates the usefulness of the system for gene expression analysis in vivo.

Animals↗
PubMed1997

Susceptibility to the development of pigment cell tumors in a clone of the Amazon molly, Poecilia formosa, introduced through a microchromosome.

The Amazon molly Poecilia formosa is a gynogenetic fish that reproduces through the development of ameiotic diploid eggs triggered by insemination by males of related species without following karyogamie. This leads to clonal offspring. In rare cases, however, this gynogenesis is leaky, and paternal DNA in the form of small supernumerary chromosomes is included into the maternal genome. We have obtained a clone where one such microchromosome contains a pigmentary locus, resulting in macromelanophore pigmentation of the carrier. Approximately 5% of these fish spontaneously develop exophytic nodular or papillomatous pigment cell tumors. The tumors display considerable differences with respect to growth characteristics and invasiveness, despite the genetic uniformity of the affected animals. Following transplantation to syngeneic hosts, a remarkable clonal variability was observed. Oncogenes that are involved in tumorigenesis in hereditary melanoma of the closely related fish Xiphophorus appear not to be instrumental for induction of the P. formosa pigment cell tumors. Moreover, a new genetic locus is defined that mediates susceptibility to pigment cell tumor development and leads to transformation of chromatoblasts.

Animals↗
PubMed1997

Activation of transcription of the melanoma inducing Xmrk oncogene by a GC box element.

Melanoma formation in Xiphophorus is caused by overexpression of the Xmrk gene. The promoter region of the Xmrk oncogene differs strikingly from the corresponding proto-oncogenic sequences and was acquired in the course of a nonhomologous recombination with another gene locus, D. In order to identify regulatory elements leading to the strong transcriptional activation of Xmrk in melanoma tissue and to contribute to an understanding of the role the regulatory locus R might play in suppressing the tumor phenotype in wild-type Xiphophorus, we performed functional analysis of the Xmrk oncogene promoter. Transient transfections in melanoma and nonmelanoma cells revealed the existence of a potent positive regulatory element positioned close to the transcriptional start site. Contained within this promoter segment is a GC-rich sequence identical to the binding site described for human Sp1. In vitro binding studies and biochemical characterizations demonstrated the existence of GC-binding proteins in fish that share immunological properties with members of the human Sp family of transcription factors and appear to be involved in the high transcriptional activation of the Xmrk oncogene. Since the identified cis element is functional in both melanoma and nonmelanoma cells, additional silencer elements suppressing Xmrk expression in nonpigment cells must exist, thereby suggesting a negative regulatory function for the genetically defined R locus.

Animals↗
PubMed1997

Phenotypic rescue of the albino mutation in the medakafish (Oryzias latipes) by a mouse tyrosinase transgene.

Mutations of the tyrosinase gene are one common cause of a similar phenotype in all vertebrates, known as albinism. In an attempt to contribute to an understanding of the genetic hierarchy governing the development of pigmentation, we have used a mouse tyrosinase minigene under the control of its 5.2 kb upstream promoter region to rescue two different albino mutations in the medakafish, Oryzias latipes. Around hatching stages an almost perfect phenocopy of the wildtype pigmentation was obtained. Subsequent ectopic melanin overproduction indicated a possible incompatibility of the heterologous mouse promoter for stable expression during the entire ontogenesis. Like in some tyrosinase transgenic mouse lines a strong variegation effect was observed. The transgene-mediated pigmentation phenotype was obtained up to the eighth offspring generation. The phenotypic effects of the tyrosinase transgene in different albino mutant strains places the i3-locus upstream and the b-locus downstream of the tyrosinase locus i1 in the genetic hierarchy leading to wildtype pigmentation.

Albinism↗
PubMed1997

Cytogenetics of the genus Leporinus (Pisces, Anostomidae). II. Molecular cytogenetics, organization and evolutionary conservation of a chromosome-specific satellite DNA from Leporinus obtusidens.

A chromosome-specific satellite DNA from the South American fish species Leporinus obtusidens has been isolated and characterized. Sequence analysis and Southern hybridization studies indicate that the cloned 483-bp fragment is 60% AT rich and appears to comprise two diverged monomers. A highly variable low-copy number polymorphism was detected and, thus, this satellite DNA may serve as a valuable genetic marker. Using a Southern blot approach, the cloned satellite DNA cross-hybridized strongly to the DNA of Leporinus elongatus but failed to detect homologous sequences in the genomes of other closely related Leporinus species and higher vertebrates. Using fluorescence in situ hybridization to mitotic metaphase spreads of L. obtusidens and L. elongatus, this satellite DNA was located to the (peri)centromeric region of one single chromosome pair in both species. As the cloned satellite DNA sequence clearly evolved along a chromosomal lineage and is highly variable, it may serve as a very useful marker in further genetic, molecular and cytogenetic studies of the genus Leporinus.

Animals↗
PubMed1997

Stress echocardiography in special groups: in women, in left bundle branch block, in hypertension and after heart transplantation.

The non-invasive diagnosis of coronary artery disease by exercise electrocardiography is less accurate in women than in men, with a high rate of false-positive results in women. In contrast, recent studies have demonstrated that stress echocardiography in women is more accurate than exercise echocardiography and that the significantly higher specificity of stress electrocardiography may have the benefit of avoiding unnecessary angiography in women. Exercise-induced changes in the electrocardiogram are non-diagnostic in the presence of left bundle branch block or basal ST changes. In these patients, stress echocardiography can be used instead of conventional scintigraphy for the detection of coronary artery disease, but further echocardiographic studies are needed to confirm the promising results. Exercise electrocardiography and exercise echocardiography have been reported to be disappointing in the early detection of cardiac allograft vasculopathy after heart transplantation, and dobutamine stress echocardiography overestimates the incidence of angiographic evidence of cardiac allograft vasculopathy. However, compared to intravascular ultrasound imaging, dobutamine stress echocardiography seems to be a suitable non-invasive method for detecting cardiac allograft vasculopathy.

Bundle-Branch Block↗
PubMed1997

Intravascular ultrasound assessment of direct percutaneous transluminal coronary angioplasty in patients with acute myocardial infarction.

BACKGROUND: Acute myocardial infarction is caused by sudden thrombotic occlusion of the coronary artery due to a previous rupture of atherosclerotic plaque. OBJECTIVE: To use intracoronary ultrasound measurements to evaluate lumen and plaque changes in patients with acute myocardial infarction. METHODS: Patients (n = 103) with acute myocardial infarction who had been scheduled to undergo primary percutaneous transluminal coronary angioplasty (PTCA) were selected. Both before and after successful coronary angioplasty, intracoronary 30 MHz ultrasound studies were performed using a 3.5F monorail catheter. The ultrasound catheter was successfully advanced into the occluded vessel segment without major complications prior to PTCA in 79 of 103 (76.7%) patients and after PTCA in 88 of 103 (85.3%) patients. RESULTS: The plaques were eccentric in 66 patients (83.5%). The plaque morphology was purely low echogenic in 14 (17.7%), highly echogenic in six (7.6%) and mixed in 59 (74.7%) patients. Partial (59 of 79, 74.7%) or ring-like calcification (3 of 79, 3.8%) was observed in 62 patients (78.5%). Plaque fissuring or dissection was detected prior to PTCA in 25 patients (31.7%). Coronary angioplasty successfully enlarged the inner luminal area from 2.1 +/- 0.7 to 7.4 +/- 1.9 mm2 (P < 0.01), whereas the plaque-thrombus area decreased significantly (13.8 +/- 1.7 mm2 before and 9.0 +/- 1.9 mm2 after PTCA; P < 0.01). The total vessel area remained virtually constant (15.9 +/- 1.9 mm2 before and 16.4 +/- 2.5 mm2 after PTCA, NS). PTCA-induced plaque rupture or dissection was observed in only 13 (16.5%) patients. CONCLUSION: Intracoronary ultrasound imaging can be performed safely and successfully prior and subsequent to PTCA in selected patients with acute myocardial infarction. Early reperfusion via PTCA seems to be attributable to a significant reduction in the amount of low-echogenic plaque and thrombus material, whereas factors like balloon-induced dissection and stretching of vessels play only a minor role.

Aged↗
PubMed1997

Hypomethylation of the Xmrk oncogene promoter in melanoma cells of Xiphophorus.

Melanoma formation in Xiphophorus is caused by the tissue-specific overexpression of the Xmrk oncogene. This gene arose by a non-homologous recombination event between the Xmrk proto-oncogene and an unrelated locus, D, during which the Xmrk transcribed regions were fused to new upstream sequences. Functional analyses of this newly acquired promoter revealed the presence of positive regulatory elements. Since these elements did not activate transcription in a melanoma-specific manner, the methylation state of the Xmrk oncogene promoter in different tissues was analyzed. Digestion with methylation sensitive restriction enzymes followed by PCR amplification demonstrated differential methylation in a melanoma cell line and non-melanoma tissue. The methylation state of single CpG-dinucleotides in genomic DNA from different cell types was investigated by bisulfite genomic sequencing. This analysis revealed a high degree of methylation of the Xmrk oncogene promoter in non-transformed tissues. In contrast, the DNA-region analyzed was completely unmethylated in the melanoma cell line PSM. This effect was oncogene-specific, since the Xmrk proto-oncogene showed CpG-methylation in these cells. Studies with melanoma tissue demonstrated that hypomethylation of the Xmrk oncogene promoter can also be found in DNA from these tumors. This correlation suggests that the methylation status of the promoter might play a role in the overexpression of the Xmrk oncogene in vivo.

Animals↗
PubMed1996

Clustered organization and conservation of the Xiphophorus maculatus D locus, which includes two distinct gene sequences.

Genomic organization and chromosomal localization of a previously uncharacterized D (Donor) locus in Xiphophorus and Poecilia species was investigated using fluorescence in situ hybridization (FISH) and Southern blot analysis. Part of this region is thought to be involved in the recombination event leading to formation of the Xmrk oncogene and it has recently been shown that this locus includes two different genes, one with high homology to a zinc finger protein of the Krüppel type, and the other an unknown gene with high similarity to a Caenorhabditis elegans gene. FISH to Xiphophorus chromosomes revealed that these two unrelated genes are closely linked and clustered at a unique chromosomal site. Southern blot hybridization patterns suggest that these genes exist in the genome as multiple copies. Furthermore, similar genomic organization profiles seem to prevail among other related fish. In particular, our FISH experiments reveal the existence of a conserved homologous chromosomal segment harboring the zinc finger protein sequence in several poeciliid fish.

Animals↗
PubMed1996

Pluripotency and differentiation of embryonic stem cell lines from the medakafish (Oryzias latipes).

Small aquarium fish, like the medaka and zebrafish, offer an excellent opportunity to combine embryological, genetic and molecular analyses of vertebrate development. Pluripotent embryonic stem (ES) cells have enormous potential to study the totipotency and differentiation of cells and provide s bridge linking in vitro manipulations of the genome. In this report we describe the establishment, pluripotency and differentiation of medaka ES-like cell lines (MES). The MES cells exhibit stable growth over 18 months of culture with 100 passages using defined culture conditions in the absence of feeder layer cells. They have a normal karyotype and form colonies of densely packed, alkaline phosphatase-positive cells resembling undifferentiated mouse ES cells. In suspension culture they form embryoid bodies, and under appropriate conditions, differentiate into a variety of cell types.

Alkaline Phosphatase↗
PubMed1996

The Xmrk oncogene promoter is derived from a novel amplified locus of unusual organization.

Hereditary melanoma in Xiphophorus hybrids is caused by the receptor tyrosine kinase Xmrk. Tumor formation is initiated by overexpression of the Xmrk gene, apparently because of insufficient transcriptional control in the melanocytic lineage of hybrid fish. The oncogenic Xmrk resulted from gene duplication and nonhomologous recombination of the corresponding Xmrk proto-oncogene during evolution. By this event Xmrk was translocated downstream of the promoter of another gene, D (for Donor). This raised the question whether both the Xmrk oncogene and D share similar transcriptional control elements. Studies on the genomic organization of D showed that this gene is amplified in the Xiphophorus genome, presumably with all copies clustered on a single chromosome. Surprisingly, at least two completely different, tightly linked genes are included in the amplified segment. We find a ubiquitously expressed zinc finger gene of the krüppel type, followed by a previously unknown gene, which was the partner of the Xmrk proto-oncogene in the recombination generating the Xmrk oncogene. The nucleotide sequence predicts a gene product with very high amino acid similarity to a hypothetical Caenorhabditis elegans protein. The expression pattern is unrelated to that of the Xmrk oncogene suggesting that despite extended sequence homology a new type of promoter was created by this rearrangement.

Amino Acid Sequence↗