Genetic restriction of HIV-1 pathogenesis to AIDS by promoter alleles of IL10

IL10 is a powerful TH-2 cell cytokine produced by lymphoid cells that limits HIV-1 replication in vivo, ostensibly by inhibiting macrophage/monocyte and T-cell lymphocyte replication and secretion of inflammatory cytokines (IL1, TNFalpha, IL6, IL8, and IL12). A genetic epidemiological scan of patients enrolled in AIDS cohorts for candidate gene-linked short tandem repeat polymorphisms revealed significant genotype associations for HIV-1 infection and progression to AIDS with markers adjacent to and tracking (by linkage disequilibrium) common single nucleotide polymorphic variants in the IL10 promoter region. Individuals carrying the IL10-5'-592A (IL10-5'A) promoter allele possibly were at increased risk for HIV-1 infection, and once infected they progressed to AIDS more rapidly than homozygotes for the alternative IL10-5'-592 C/C (IL10-+/+) genotype, particularly in the later stages of HIV-1 infection. An estimated 25-30% of long-term nonprogressors (who avoid clinical AIDS for 10 or more years after HIV-1 infection) can be attributed to their IL10-+/+ promoter genotype. Alternative IL10 promoter alleles are functionally distinct in relative IL10 production, in retention of an avian erythroblastosis virus transcription factor recognition sequence and in binding to specific putative nuclear transcription factors, suggesting a potential mechanism whereby IL10-5'A down-regulation of inhibitory IL10 facilitates HIV-1 replication in vivo, accelerating the onset of AIDS.

[Doxycycline--the forgotten antibiotic]

BACKGROUND

Doxycycline is an broad-spectrum antimicrobial agent, it remains an inexpensive alternative for the treatment of community-acquired respiratory infections and urinary tract infections. Despite these clinical data the use of doxycycline has decreased during the last years.

PHARMACOLOGY

Adverse effects and resistance to therapy are infrequent and not different to fluoroquinolones and macrolide antibiotics. Gastrointestinal and phototoxic side effects are of importance. After oral administration 75% will be absorbed and largely eliminated by the hepatic and intestinal way. Contraindications are severe liver dysfunction and treatment in childhood.

CLINICAL INDICATIONS

Bacterial resistance to doxycycline has a low incidence in Germany. A therapeutic success can be expected in respiratory and urinary tract infections in about 80%. Doxycycline is the drug of choice for treating infections caused by Rickettsia, Borrelia, Ehrlichia. It shows good activity against Plasmodium falciparum as one part in a combination therapy. Daily costs of therapy are low, in oral administration DM 0.80 per day, in i.v. administration DM 22,-per day.

CONCLUSION

Despite competition from new antibiotics, doxycycline can retain an important place in the treatment of many infectious diseases.

Genetic heterogeneity and molecular epidemiology of GB virus C/hepatitis G virus in China

OBJECTIVE

The inter- and intrapatient genetic variation of GB virus C (GBV-C)/hepatitis G virus (HGV) was investigated to characterize the molecular epidemiologic profile of GBV-C/ HGV infection in China, an area endemic for viral hepatitis. The intrapatient variation of hepatitis C virus (HCV) from the same patients was compared to that of GBV-C/HGV.

STUDY DESIGN/METHODS

GB virus C/HGV RNA was amplified by polymerase chain reaction in 88 patients with hepatitis C, hepatitis B or presumed non-A-E hepatitis from three cities in China. Five clones of the GBV-C/HGV NS3 region were sequenced from each GBV-C/HGV RNA-positive patient. The corresponding region of HCV was also sequenced from patients co-infected with HCV. Representative sequences of the GBV-C/HGV NS3 region from each patient and those of isolates from other continents were subjected to phylogenetic analyses.

RESULTS

GB virus C/HGV was detected in 22 (25.25%) of 88 patients: 9 (21.4%) of 42 patients with presumed non-A-E hepatitis, 10 (27.7%) of 36 patients with hepatitis C, 3 (30.0%) in 10 patients with hepatitis B and C, and in none of 60 volunteer blood donors. The extent of nucleotide variation was less between Chinese isolates (2.4-17%; median, 10.4%) than between Chinese isolates and seven isolates from outside China (10.5-19.5%; median, 15.3%). Intrapatient sequence variation ranged from 0 to 1.75%, with a mean of 0.57 +/- 0.51%. Phylogenetic analysis grouped most Chinese isolates into four geographically specific clusters with a divergence of 10% to 16% from each other. The ratio of nonsynonymous to synonymous substitutions of GBV-C/HGV (Ka/Ks 0.019) was much lower than for HCV (0.071) in the same patients.

CONCLUSION

Chinese isolates of GBV-C/HGV are genetically distinct. There are local strains as well as shared strains between different locales. The extent of amino acid sequence conservation suggests strong selection against nonsynonymous substitutions in the GBV-C/HGV genome.

EGF infusion stimulates the proliferation and migration of embryonic progenitor cells transplanted in the adult rat striatum

Immature progenitor cells (generated by in vitro propagation) may provide a useful alternative to primary cells (from dissected embryonic tissue) for transplantation if their migratory and proliferative and differentiation properties can be controlled and directed in vivo. In this study E15 murine EGF-responsive progenitor cells were transplanted to the striatum of adult rats. Simultaneously, these animals received continuous infusion of either epidermal growth factor (EGF) or vehicle, to the lateral ventricle, for 8 days. In animals that received EGF, the transplanted progenitors migrated toward the lateral ventricle and proliferated, as evidenced by bromodeoxyuridine incorporation. Progenitor cells transplanted to rats that received vehicle infusions showed neither of these responses. In all animals, transplanted progenitors expressed an immature astrocyte or oligodendrocyte phenotype, the majority of cells being astrocytes. We conclude that EGF stimulates the migration and proliferation of murine progenitor cells in vivo, either directly or indirectly, but does not influence their phenotypic differentiation.

Primary structure and expression of the xiphophorus DNA-(cytosine-5)-methyltransferase XDNMT-1

Small aquarium fishes become increasingly important in the study of normal vertebrate development and disease. Differential DNA methylation might play a role in these processes. In the teleost Xiphophorus, a well-established animal model for melanoma formation, tumour-specific hypomethylation of the melanoma-inducing gene ONC-Xmrk has been observed. We have isolated a cDNA for the DNA-(cytosine-5)-methyltransferase XDNMT-1 from this organism, which encodes the first full-length protein from a fish species. Linkage analysis showed that Xdnmt-1 is different from the Xiphophorus tumour suppressor R, which is involved in the transcriptional repression of the ONC-Xmrk melanoma oncogene in healthy fish. As methylation has been implicated in the regulation of ONC-Xmrk expression, XDNMT-1 might play a role by acting up- or downstream of R. Expression analysis demonstrated that the Xdnmt-1 transcript is present in all adult tissues and cell lines tested. However, developing embryos show a spatially and temporally regulated expression pattern suggesting that the enzyme might play a role during development in fish.

Complex sensorimotor behavioral changes after terminal striatal 6-OHDA lesion and transplantation of dopaminergic embryonic micrografts

In this study sensorimotor behavioral changes were monitored in rats following bilateral 6-hydroxydopamine (6-OHDA) axon terminal lesion and uni- or bilateral implantation of embryonic dopaminergic (DA) micrografts. A total of 28 microg of 6-OHDA was distributed over four injection tracts in the dorsolateral part of the caudate-putamen (CPU) bilaterally followed 4 months later by the implantation of DA micrografts spread over seven implantation tracts placed within the denervated area. Bilaterally 6-OHDA-lesioned animals exhibited significantly reduced behavioral performance scores in tests of explorational and stepping behavior as well as in skilled forelimb use. However, in contrast to the established medial forebrain bundle (MFB) lesion model of PD, these animals showed a spontaneous recovery in the side falling and skilled forelimb behavior and no deficits in overnight locomotor activity at 6 months after the lesion. Unilateral DA micrografts elicited a substantial amphetamine-induced rotational bias contralateral to the graft, but led to a significant impairment of contralateral skilled forelimb use and reduced scores in overnight locomotor activity. Bilateral DA micrografts caused a significant, though partial, increase in explorational and backhand stepping behavior, but resulted also in a significant decrease in performance levels in overnight locomotor activity and skilled forelimb use on both paws. In conclusion, DA grafts placed ectopically in the CPU in the partial lesion model of PD result in a double innervation of the GABAergic striatal neurons, arising from the residual nigrostriatal DA projections of the host and from the graft-derived DA efferent fibers. These two DA fiber systems may indeed function in a cooperative and competitive manner depending on their respective and different afferent and efferent connections, which, in turn, may lead to positive or negative influences on basal ganglia function and behavioral performances. The different patterns of 6-OHDA lesion and transplant-induced behavioral changes demonstrated in the present study compared to the "classical" MFB lesion model of PD may thus provide further insights in the complex functional organization of the basal ganglia and, thereby, may help to further optimize restorative strategies for neurodegenerative diseases, such as Parkinson's disease.

Effects of plasma HIV RNA, CD4+ T lymphocytes, and the chemokine receptors CCR5 and CCR2b on HIV disease progression in hemophiliacs. Hemophilia Growth and Development Study

We have investigated the effects of plasma HIV RNA, CD4+ T lymphocytes and chemokine receptors CCR5 and CCR2b on HIV disease progression in hemophiliacs. We prospectively observed during follow-up 207 HIV-infected hemophiliacs in the Hemophilia Growth and Development Study. Plasma HIV RNA was measured on cryopreserved plasma from enrollment using the Chiron Corporation bDNA (version 2.0) assay. Genoytpe variants CCR2b-641 and CCR5-delta32 were detected using standard molecular techniques. Those with the mutant allele for CCR2b, and to a lesser extent CCR5, had lower plasma HIV RNA, and higher CD4+ T lymphocytes than did those without these genetic variants. After controlling for the effects of plasma HIV RNA and CD4+ T lymphocytes, those with the CCR2b mutant allele compared with those wild-type, had a trend toward a lower risk of progression to AIDS, adjusted relative hazard of 1.94 (95% confidence interval [CI], 0.9-4.18; p = .092), and AIDS-related death, relative hazard 1.97 (95% CI, 0.98-4.00; p = .059). We conclude that plasma HIV RNA, CD4+ T lymphocytes, and CCR genotypes are correlated, and the protective affect of CCR2b against HIV disease progression is not completely explained by plasma HIV RNA or CD4+ T-lymphocyte number.

Site-specific migration and neuronal differentiation of human neural progenitor cells after transplantation in the adult rat brain

Neural progenitor cells obtained from the embryonic human forebrain were expanded up to 10(7)-fold in culture in the presence of epidermal growth factor, basic fibroblast growth factor, and leukemia inhibitory growth factor. When transplanted into neurogenic regions in the adult rat brain, the subventricular zone, and hippocampus, the in vitro propagated cells migrated specifically along the routes normally taken by the endogenous neuronal precursors: along the rostral migratory stream to the olfactory bulb and within the subgranular zone in the dentate gyrus, and exhibited site-specific neuronal differentiation in the granular and periglomerular layers of the bulb and in the dentate granular cell layer. The cells exhibited substantial migration also within the non-neurogenic region, the striatum, in a seemingly nondirected manner up to approximately 1-1.5 mm from the graft core, and showed differentiation into both neuronal and glial phenotypes. Only cells with glial-like features migrated over longer distances within the mature striatum, whereas the cells expressing neuronal phenotypes remained close to the implantation site. The ability of the human neural progenitors to respond in vivo to guidance cues and signals that can direct their differentiation along multiple phenotypic pathways suggests that they can provide a powerful and virtually unlimited source of cells for experimental and clinical transplantation.

New class I and II HLA alleles strongly associated with opposite patterns of progression to AIDS

The genetics of resistance to infection by HIV-1 cohort consists of 200 slow and 75 rapid progressors to AIDS corresponding to the extremes of HIV disease outcome of 20,000 Caucasians of European descent. A comprehensive analysis of HLA class I and class II genes in this highly informative cohort has identified HLA alleles associated with fast or slow progression, including several not described previously. A quantitative analysis shows an overall HLA influence independent of and equal in magnitude (for the protective effect) to the effect of the CCR5-Delta32 mutation. Among HLA class I genes, A29 (p = 0.001) and B22 (p < 0.0001) are significantly associated with rapid progression, whereas B14 (p = 0.001) and C8 (p = 0.004) are significantly associated with nonprogression. The class I alleles B27, B57, C14 (protective), and C16, as well as B35 (susceptible), are also influential, but their effects are less robust. Influence of class II alleles was only observed for DR11. These results confirm the influence of the immune system on disease progression and may have implications on peptide-based vaccine development.

Intranigral transplants of GABA-rich striatal tissue induce behavioral recovery in the rat Parkinson model and promote the effects obtained by intrastriatal dopaminergic transplants

Intrastriatal transplantation of fetal ventral mesencephalon (VM) is currently explored as a potential clinical therapy in Parkinson's disease (PD). Although providing substantial benefit for the patient, behavioral recovery so far obtained with intrastriatal VM grafts is not complete. Using the 6-hydroxydopamine lesion model of PD, we show here that near-complete restoration of the striatal dopamine (DA) innervation can be achieved by multiple intrastriatal microtransplants of fetal DA cells; nevertheless, complete recovery in complex sensorimotor behaviors was not obtained in these animals. In line with the current model of basal ganglia function, this suggests that the lesion-induced overactivity of the basal ganglia output structures, i.e., the substantia nigra (SN) and the entopeduncular nucleus, may not be completely reversed by intrastriatal VM grafts. In the present study, we have transplanted fetal VM tissue or fetal striatal tissue, as a source of DA and GABA neurons, respectively, into the SN of DA-depleted rats. Intranigral VM grafts induced behavioral recovery in some sensorimotor behaviors (forelimb akinesia and balance tests), but the effect did not exceed the recovery observed after intrastriatal VM grafts. Intranigral grafts of striatal tissue induced a pattern of functional recovery which was distinctly different from that observed after intranigral VM grafts, and recovery in coordinated forelimb use in the paw-reaching test was even more pronounced than after intrastriatal transplantation of VM cells. Combined transplantation of DA neurons into the striatum and GABA-rich striatal neurons into the SN induced additive effects of behavioral recovery observed in the forelimb akinesia test. We propose that intranigral striatal transplants, by a GABA-mediated inhibitory action, can reduce the overactivity of the host SN projection neurons and can induce significant recovery in complex motor behavior in the rat PD model and that such grafts may be used to increase the overall functional efficacy of intrastriatal VM grafts.

Relation of plasma leptin to lipoproteins in overweight children undergoing weight reduction

BACKGROUND

In obese children, plasma leptin is elevated and correlates with the body mass index (BMI). In obese adults, plasma leptin decreases during weight reduction. Since the leptin system changes dynamically in puberty, we asked whether weight reduction in obese adolescents has similar consequences for plasma leptin as in overweight adults. In plasma, a portion of leptin is bound to several as yet uncharacterised proteins. We therefore studied the possible association of leptin with plasma lipoproteins.

SUBJECTS AND METHODS

We measured plasma leptin, lipoprotein cholesterol and apolipoproteins (apo) A-I and B in 34 obese children (age 12.5+/-1.9 y, relative BMI 165.0+/-28.1%) before and after three weeks of weight reduction in a dietary camp. Lipoprotein binding of endogenous and exogenously radiolabelled leptin was studied by preparative ultracentrifugation.

RESULTS

Plasma leptin was higher in obese children than in normal weight controls and fell from 16.5+/-9.8 ng/ml to 10.0+/-8.6 ng/ml after weight reduction (P < 0.001). In multivariate regression, relative BMI and apoA-I were significant predictors of baseline leptin and accounted for 38% (P = 0.003) and 15% (P = 0.006) of the variance of baseline leptin concentrations in obese children. Only the difference in plasma high-density lipoprotein (HDL)-cholesterol independently predicted the change of plasma leptin that was associated with weight reduction, explaining 29% of the variance of leptin changes (P = 0.0032). A substantial portion of both endogenous and exogenously labelled leptin was recovered with HDL isolated by ultracentrifugation.

CONCLUSIONS

We conclude that plasma leptin decreases in overweight children undergoing short term weight reduction. In obese children, plasma apoA-I and HDL-cholesterol are independent predictors of leptin concentrations during weight loss, respectively. In addition, HDLs transport a variable portion of leptin in the circulation.

Genetic acceleration of AIDS progression by a promoter variant of CCR5

The CCR5 gene encodes a cell surface chemokine receptor molecule that serves as the principal coreceptor, with CD4, for macrophage-tropic (R5) strains of human immunodeficiency virus-type 1 (HIV-1). Genetic association analysis of five cohorts of people with acquired immunodeficiency syndrome (AIDS) revealed that infected individuals homozygous for a multisite haplotype of the CCR5 regulatory region containing the promoter allele, CCR5P1, progress to AIDS more rapidly than those with other CCR5 promoter genotypes, particularly in the early years after infection. Composite genetic epidemiologic analyses of genotypes bearing CCR5P1, CCR5-Delta32, CCR2-64I, and SDF1-3'A affirmed distinct regulatory influences for each gene on AIDS progression. An estimated 10 to 17 percent of patients who develop AIDS within 3.5 years of HIV-1 infection do so because they are homozygous for CCR5P1/P1, and 7 to 13 percent of all people carry this susceptible genotype. The cumulative and interactive influence of these AIDS restriction genes illustrates the multigenic nature of host factors limiting AIDS disease progression.

Efficiency of cell culture derivation from blastula embryos and of chimera formation in the medaka (Oryzias latipes) depends on donor genotype and passage number

Embryonic stem (ES) cells from early vertebrate embryos only rarely retain their full developmental potential under in vitro culture conditions, but undergo differentiation and lose their ability for chimeric embryogenesis. This is reflected by the fact that the ES cell technology to date could only be fully developed in mice. In the fish Oryzias latipes, the medaka, one ES-like cell line, MES1, has been established which gives rise to a high frequency of somatic chimeras but a low degree of chimerism. Here we have tested the effect of donor genotype and cultivation time on the efficiency of cell culture derivation and on chimera formation. The HB12A, HB32C and HNI strains of medaka most efficiently and reproducibly give rise to blastula-derived cell cultures that produce pigmented chimeras in albino hosts. Seven chimeras grew to male or female adults with normal fertility, although none of them showed obvious donor germline contribution. During prolonged in vitro propagation the frequency of chimeras and the degree of chimerism dropped to a value retained in the long-term cultured MES1 cells. Obviously, genetic factors in host/donor compatibility and physiological changes during prolonged in vitro culture may compromise, but do not abolish, the developmental potential of medaka ES-like cells. Thus, elucidation of conditions that will expand the developmental potential of medaka blastula cell cultures should lead to a further improvement towards establishment of the ES cell technology in medaka.

[The results of radiotherapy in meningiomas with a high risk of recurrence. A retrospective analysis]

AIM

Retrospective assessment of the efficacy of radiation therapy for meningiomas with high risk for local recurrence.

PATIENTS AND METHODS

Records of 67 patients with meningiomas treated from 1974 to 1995 at 2 centres were analyzed. Follow-up time ranged from 0.8 to 213 months (median: 61 months). Radiation therapy was given either after local failure or after biopsy or subtotal resection. The ratio between malignant (n = 20) and benign (n = 47) meningioma was 1:2.4. Median age of the patients was 55 years (7 to 77 years). Radiation treatment was given at 1.5 to 2 Gy per fraction to 36 to 79.5 Gy. Survival rates were calculated by the Kaplan-Meier method. Statistical comparisons were performed with the log-rank test and the Cox proportional hazards model. The Bonferroni method was used to correct for multiple comparisons.

RESULTS

Five- and 10-year disease-free survival rates were 82% +/- 5% (standard error) and 70% +/- 9%. Local control rates at 5 and 10 years were 78% +/- 5% and 68% +/- 9%. In uni- and multivariate analysis histology, sex, total dose and center showed no significant influence on the results. Patients age was significant for local control (univariate p = 0.02; multivariate p = 0.03) and disease-free survival (univariate/multivariate p = 0.04). The postoperative tumor burden had a significant influence of disease-free survival (multivariate p = 0.04). After Bonferroni correction no significant influence was observed. We did not observe late side effects, especially brain necrosis.

CONCLUSIONS

Despite of the negative selection of our patients we observed high survival- and local control rates after radiation therapy. This underscores the role of radiation therapy in the treatment of meningiomas with high risk of local failure.

Plasma leptin levels: interaction of obesity with a common variant of insulin receptor substrate-1

Obesity is associated with insulin resistance and other major cardiovascular risk factors. A common amino acid polymorphism at codon 972 of the insulin receptor substrate-1 (IRS-1) has been shown to interact with obesity in the expression of insulin resistance. The plasma concentration of the adipocyte-specific hormone leptin is increased in obesity and is correlated with adipose tissue mass. Because in vitro studies demonstrated inhibitory effects of leptin on insulin signaling, leptin may be involved in obesity-associated insulin resistance. To gain insight into the relationship between insulin and leptin in obesity, we studied plasma leptin levels and several cardiovascular risk factors, as well as their modification by the IRS-1 codon 972 genotype, in 156 obese individuals and 131 lean control subjects. In both groups, 10% of the subjects were heterozygous for the IRS-1 codon 972 variant. Obese individuals harboring the IRS-1 variant displayed significantly lower plasma concentrations of leptin than obese subjects without the polymorphism (means, 26.7 versus 37.8 ng/mL, P<0.0293). In a subgroup of obese patients, leptin mRNA abundance was measured in the adipose tissue and was significantly lower in carriers of the IRS-1 variant than in subjects with the wild-type variant (P<0.0291). Our data suggest that insulin signaling influences plasma leptin concentrations at the mRNA expression level and argue against leptin as a major causative factor of insulin resistance.

Incorporation and glial differentiation of mouse EGF-responsive neural progenitor cells after transplantation into the embryonic rat brain

In vitro, epidermal growth factor (EGF)-responsive neural progenitor cells exhibit multipotent properties and can differentiate into both neurons and glia. Using an in utero xenotransplantation approach we examined the developmental potential of EGF-responsive cells derived from E14 mouse ganglionic eminences, cortical primordium, and ventral mesencephalon, after injection into the E15 rat forebrain ventricle. Cell cultures were established from control mice or from mice carrying the lacZ transgene under control of the promoters for nestin, glial fibrillary acidic protein (GFAP), or myelin basic protein (MBP). The grafted cells, visualized with mouse-specific markers or staining for the reporter gene product, displayed widespread incorporation into distinct forebrain and midbrain structures and differentiated predominantly into glial cells. The patterns of incorporation of cells from all three regions were very similar without preference for the homotopic brain areas. These results suggest that EGF-responsive progenitor cells can respond to host derived environmental cues, differentiate into cells with glial-like features, and become integrated in the developing recipient brain.

Dating the origin of the CCR5-Delta32 AIDS-resistance allele by the coalescence of haplotypes

The CCR5-Delta32 deletion obliterates the CCR5 chemokine and the human immunodeficiency virus (HIV)-1 coreceptor on lymphoid cells, leading to strong resistance against HIV-1 infection and AIDS. A genotype survey of 4,166 individuals revealed a cline of CCR5-Delta32 allele frequencies of 0%-14% across Eurasia, whereas the variant is absent among native African, American Indian, and East Asian ethnic groups. Haplotype analysis of 192 Caucasian chromosomes revealed strong linkage disequilibrium between CCR5 and two microsatellite loci. By use of coalescence theory to interpret modern haplotype genealogy, we estimate the origin of the CCR5-Delta32-containing ancestral haplotype to be approximately 700 years ago, with an estimated range of 275-1,875 years. The geographic cline of CCR5-Delta32 frequencies and its recent emergence are consistent with a historic strong selective event (e.g. , an epidemic of a pathogen that, like HIV-1, utilizes CCR5), driving its frequency upward in ancestral Caucasian populations.

Activation of the Xmrk proto-oncogene of Xiphophorus by overexpression and mutational alterations

Xmrk is a receptor tyrosine kinase closely related to the human EGF receptor. In the teleost fish Xiphophorus two versions of the Xmrk gene exist, an oncogene (ONC) and a proto-oncogene (INV). While ONC-Xmrk is the melanoma-inducing gene, INV-Xmrk appears not to be involved in transformation of pigment cells. To elucidate the mechanism that converts the proto-oncogene into a transforming oncogene a comparative analysis of the structure, expression and function of both versions of the gene was performed. In contrast to ONC-Xmrk which is expressed at high levels in melanoma cells, the proto-oncogene INV-Xmrk is ubiquitously expressed at very low levels indicating overexpression as one possible reason for tumorigenicity by ONC-Xmrk. As sequence comparison of the proto-oncogene and the oncogene revealed a number of amino acid changes, a possible effect of these mutations on the activation of the ONC-Xmrk receptor was determined. A constitutive activation of the oncogenic receptor was found and ectopic expression of INV-Xmrk after microinjection into medakafish embryos did not lead to the high tumour rate in transgenic fish as observed for the oncogene. Our data therefore suggest that overexpression of the receptor alone is not sufficient for melanoma induction, but that in addition activating mutations in ONC-Xmrk are responsible for its full tumorigenic potential.

Production of medakafish chimeras from a stable embryonic stem cell line

Embryonic stem (ES) cell lines provide a unique tool for introducing targeted or random genetic alterations through gene replacement, insertional mutagenesis, and gene addition because they offer the possibility for in vitro selection for the desired, but extremely rare, recombinant genotypes. So far only mouse blastocyst embryos are known to have the competence to give rise to such ES cell lines. We recently have established a stable cell line (Mes1) from blastulae of the medakafish (Oryzias latipes) that shows all characteristics of mouse ES cells in vitro. Here, we demonstrate that Mes1 cells also have the competence for chimera formation; 90% of host blastulae transplanted with Mes1 cells developed into chimeric fry. This high frequency was not compromised by cryostorage or DNA transfection of the donor cells. The Mes1 cells contributed to numerous organs derived from all three germ layers and differentiated into various types of functional cells, most readily observable in pigmented chimeras. These features suggest the possibility that Mes1 cells may be a fish equivalent of mouse ES cells and that medaka can be used as another system for the application of the ES cell technology.