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Impairment or loss of suppressor genes is a common event permitting the oncogene/suppressor gene machinery to develop neoplasia. Following prenatal treatment with X-rays and UV-B, we detected a new class of oncodeterminants that could not be specified as genes. This points to paragenetic elements that suppress suppressorgenes and thus provoke melanoma at earlier ages of onset as expected, with increased severity and increased number of incidences in successive generations, in the absence of further treatment. These elements were isolated from a xiphophorine DNA library by endogenously labeled long terminal repeats (LTR) of a xiphophorine retrovirus, and were characterized as retrotransposons by Southern and Northern blotting and reverse transcription/polymerase chain reaction and transient transfection studies, in situ hybridization, and sequencing. They appear in multiple copies in the telomeric chromosome regions, where they can extend. Three open reading frames (ORF) are flanked by LTR that contain genetically active regulatory elements, and are inducible by UV-B. ORF 3 shows nests of CG dinucleotides and CGG trinucleotides, which are reminiscent of CGG nests predisposing subjects to anticipation of certain human diseases involving tumor generation. Genetic anticipation as defined by Nettleship (1909) or Warren (1996) including an increase of neoplasia might represent an acquired genetic load in preceding generations, which might provide a lead to a molecular understanding of the worldwide increase of incidences of human tumor.

Uppsatsens syfte är att identifiera väsentliga påverkansfaktorer på svenskt entreprenörskap. Uppsatsens uppkomst beror på nutidens fokusering på entreprenörskap och företagande. Det genomförs många lagändringar med olika politiska krafter i bakgrunden. En viktig påverkansfaktor har varit EU. Mycket fokus ligger på företaget men färre debatter handlar om individen. Författarna undersöker entreprenörer för att se vilka variabler som är väsentliga påverkansfaktorer på entreprenöriell motivation. Uppsatsen baseras på primärdata från en enkätundersökning som författarna genomförde maj 2011. Undersökningspopulationen valdes ut genom ett icke-statistiskt urval. Primärdatan har analyserats i SPSS genom korrelationsanalyser och multipel regressionsanalys. Den genomförda undersökningen visar att mindre faktorer än vad författarna väntade sig faktiskt påverkade entreprenöriell motivation. Slutsatserna är att enbart personliga attribut påverkar individernas motivation.

A cell line (BsT) established from neoplastic embryonal tissues of the platyfish ( Xiphophorus maculatus ) released spontaneously retrovirus-like particles. The particles have a buoyant density of 1.16 g/ml, a mean diameter of 100 nm and the morphology of immature retroviruses. The particle-associated proteins p70, p65, and p28 react with an antiserum directed against the major internal feline leukemia virus structural protein p27. The particles are associated with a reverse transcriptase. The purified enzyme has a molecular weight of about 70 kDa and prefers the template primers poly(rA):oligo(dT), poly(dC):oligo(dG), and poly(rC):oligo(dG) in the presence of Mn 2+ . The enzyme activity is inhibited by antibodies directed against the reverse transcriptase of feline leukemia virus and simian sarcoma virus. The particles contain a ribonucleic acid of about 70 S. In an endogenous reverse transcriptase reaction nucleic acids in the range of 0.2 to 0.4 kb were synthesized. In Northern blots with these nucleic acids as probe, three transcripts of about 8.5, 4.2, and 1.5 kb were detected in BsT cells. Southern blot analysis with the same probe demonstrates related sequences in the DNA of BsT cells and the platyfish and swordtail ( Xiphophorus hellerl ). Hybridization experiments with the LTR-gag region of the feline leukemia virus show homologous sequences in the Xiphophorus genome .

The worldwide accelerating increase of neoplasia in humans is difficult to explain. We use the Xiphophorus tumor model to approach this problem by melanoma provocation with X-rays. Melanoma develops following inappropriate expression of x-erb B-conducted developmental genes and their controllers. These oncodeterminants are inherited according to Mendelian rules. We detected a new type of oncodeterminants that, following a single treatment of embryos with X-rays, generates a self-generating non-Mendelian melanoma transmission and accelerating increase of its incidence in succeeding generations (e.g., 0-->18-->33-->52%). To localize these oncodeterminants, we crossed nonirradiated fish having half of their chromosomes irradiated with nonirradiated fish having none of, half of, or all of their chromosomes irradiated. Because tumor rate and expression in the following generations correspond to the rates of treated chromosomes, we conclude that the new oncodeterminants are distributed over the chromosomes of the fish, where they may increase in the changing generations. By means of xiphophorine-specific retroviral DNA, we isolated two retrotransposons that behave hereditarily like the new transgenerational oncodeterminants. Sequence analysis revealed three ORFs flanked by LTRs containing motives of regulatory sequences typical for known retroviral and retrotransposal LTRs. Pol- and env-resembling sequences are lacking. Southern and in situ hybridization showed their multiple and repetitive nature distributed throughout the chromosomes and indications for their capability to increase in number without further treatment. Their transcripts are expressed in concert with those of most of the other known xiphophorine tumor determinants. Their expression is extremely high in cell cultures from tumorous embryos derived from ancestors treated as embryos with X-rays.

The melanoma determining Tu locus of the teleost Xiphophorus contains an accessory gene, x-erbB*a, which is closely related to the EGF receptor gene family, and is probably oncogenic. x-erbB*a exists in allelic forms that are specific for distinct Tu-loci, and shows high homology to a non-allelic non-oncogenic counterpart x-erbB*i which is transcribed into mRNA of 4.6 kb in non-tumorous and tumorous tissues of fish harboring and lacking Tu. Expression of a 4.0-kb mRNA in tumors (melanoma and fibrosarcoma) of different etiology is strictly correlated with the inheritance of X. maculatus x-erbB*a alleles; transcripts of 8.0 kb were detected in melanoma and carcinoma of fish harboring a certain x-erbB*a of X. variatus. The expression of the putative x-erbB*a transcripts parallels the stage of malignancy of the tumor. The expression of the xiphophorine EGF receptor gene (x-erbB) was detected in almost all tumors, is strongly enhanced in carcinoma, and is positively correlated with the degree of malignancy of melanoma and fibrosarcoma. Some tumors show expression of erbA-related genes. The PDGF receptor mRNA is expressed in all tumors analyzed and shows enhanced expression in malignant tumors of neurogenic, epithelial and mesenchymal origin. Expression of x-pdgf was observed in several cases of melanoma, but more frequently in carcinoma and fibrosarcoma. We conclude that x-erbB*a might be involved in initiation of tumors of different cellular origin and etiology in fish harboring Tu, as well as in the determination of the malignancy of the tumor. Furthermore, we assume that x-erbB*i, x-erbB, x-pdgf and x-pdgf-r play a role in secondary events in tumorigenesis by, e.g., conferring a selective growth advantage to the tumor cells.

Neoplasia is not limited to human beings, or to mammals, but can develop in all taxonomic groups of the recent Eumeta-zoa and even in multicellular plants. It therefore appears to be inherent to the multicellular organization of life [1]. The oncogenes that are associated with human cancer are also distributed throughout the animal kingdom [2–9]. Moreover, tumor-suppressor genes [10] that may control the expression of oncogenes and the manifestation of a tumor phenotype have been identified in humans and were also detected in the invertebrate Drosophila melanogaster and lower vertebrates of the genus Xiphophorus [11–17]. According to one current concept, carcinogenesis is a multistep process that includes activation of one or more “dominant acting oncogenes” and the inactivation of tumor-suppressor genes [18,19]. The lower vertebrate genus Xiphophorus offers the possibility to study both the activation of oncogenes and the inactivation of tumor-suppressor genes.

Modern cancerology is based on the oncogene concept. This is rather new. The idea of the oncogene, however, is old, and can be traced back to two sources, namely to "cancer families," reported in 1866 by P. Broka, and to "virus induced" neoplasia, detected by P. Rous in 1911. A gene which is--to my knowledge--the first reported oncogene by definition was detected in the little ornamental Mexican fish Xiphophorus by Myron Gordon, Curt Kosswig, and Georg Haussler in 1928 when they observed the terrible hereditary melanomas that we are now coming to understand and to compare with other kinds of neoplasms in Xiphophorus and in mammals, including humans. Although the Xiphophorus model was always modest in its claims, it has--sometimes too early in its history--contributed many facts to the present concept of neoplasia.

DNA polymerases have been isolated from muscle and melanoma tissues of Xiphophorus, which are similar to retroviral RNA-dependent DNA polymerases as they prefer RNA to DNA templates. They appear to associate with submicroscopic structures which exhibit a density of about 1.13 g/ml after sucrose-density-gradient centrifugation. The RNA-dependent-DNA-polymerase-like enzymes could be separated from the DNA-dependent DNA polymerases by DEAE-cellulose chromatography. Further purification on phosphocellulose revealed that the muscle enzyme eluted at the void volume and at about 0.6 M KCl, whereas most of the melanoma enzyme eluted at 0.1 M KCl. Comparison of the template primer specificities of the muscle and melanoma enzymes with those of known DNA polymerases showed obvious similarities to the RNA-dependent DNA polymerase isolated from Rous sarcoma virus.

Monoclonal antlbodies (MAbs) directed against Xiphophorus melanoma cells were deve(oped and tested by lndirect immunofluorescence and Immunoperoxidase staining for reactivity with a panel of I 5 allogeneic tissues and 12 allogeneic cell llnes. The reactivity of such MAbs was restricted to melanoma cells from tumor biopsies and melanoma-derived cell lines. ln addition, all embryonie cells of all histiotypes from developmental stages later than mld·organogenesis and from corresponding short term in vitro cultures reacted with these MAbs. ln contrast, normal tissues and organs from adult fish dlsplayed no reactivity, thus implying that the melanoma-associated antigens detected by the MAbs described are oncofetal antigens.

We report genetic transformation in an intact higher organism, i.e., in xiphophorine fish. The gene to be transferred (Tu) is responsible for the formation of T-melanophores in the platyfish and is involved in the formation of melanomas in platyfish-swordtail hybrids. After injection of Tu-donor DNA into the neural crest region of embryos from Tu-free fish, some of the recipients developed T-melanophores. In a few cases, one or two single T-melanophores were formed during late embryo-genesis. In most cases, many T-melanophores developed in young fish and were arranged in several colonies or in a pattern. DNase-degraded Tu-donor DNA, Tu-free fish DNA, as well as DNA from E. coli and adenovirus-2, did not induce T-melanophores. When using DNA from different strains of Tu-donor fish which differed in a regulating gene linked to Tu, the percentages of fish showing T-melanophores paralleled the degree of phenotypic expression of the Tu gene in the DNA donor. The results suggest that the Tu gene has been successfully transferred together with the linked regulating gene.

About 7000 animals of 65 different genotypes of the xiphophorine fish were treated with the direct acting chemical carcinogen N-methyl-N-nitrosourea (MNU; 10−3 M; four times for 1 hour in two week intervals), in order to find out, whether the susceptibility for development of fibrosarcomas and rhabdomyosarcomas is directly related to the genotype. A genotype specific susceptibility was found, ranging from zero to about nine percent. The highest susceptibilities were found in certain backcross hybrids involving P.variatus/X.helleri-hybrids and X.helleri as the recurrent parent. These genotypes were further analysed. Both P.variatus and X.helleri, as well as their F 1 proved to be insusceptible; while from the three backcrosses, which were tested, namely the BC 1, BC 4 and BC 15, both the BC 1 and the BC 4, were susceptible, but the BC 15 was insusceptible. The results are interpreted on the basis of the assumption that the differential susceptibility is a function of the type of control of a tumor gene (Tu-Fi-Rh) endogenous to P.variatus and involved in development of fibrosarcomas and rhabdomyosarcomas. Accordingly, in P.variatus and in the F1 the Tu-Fi-Rh is controlled by repressing genes (R-genes) linked as well as non-linked to Tu-Fi-Rh; because simultaneous mutation of both R-genes following treatment with MNU is an extremely unlikely event, these genotypes have an extremely low susceptibility. By contrast, in the BC 1 and the BC 4 the non-linked R-genes become eliminated and only the linked R-gene remains for repression of Tu-Fi-Rh; this condition confers a high degree of susceptibility, because one single mutation may lead to impairment of the R-gene and to Tu-Fi-Rh-mediated formation of fibrosarcomas and rhabdomyosarcomas. In the BC 15, furthermore, also the Tu-Fi-Rh has become eliminated, resulting in a loss of the susceptibility. The results suggest that in the xiphophophorine fish the susceptibility for responding to MNU-treatment with the development of fibrosarcomas and rhabdomyosarcomas is related directly to the genotype.

Most biological reactions, including carcinogenesis, are complex processes involving thousands of compounds, their metabolites and intermediates. The separation of events which form part of a direct chain leading to neoplastic transformation from those which are mere by-products is a herculean task. In this study, we focused on the pros and cons of reactive oxygen species (ROS) being involved in the development of oral cancer among chewers of tobacco and areca nuts. The results revealed that bursts of ROS generation occur at different stages of carcinogenesis, and are caused by different mechanisms. This observation may have considerable practical implications. Different strategies will be required in the administration of chemopreventive agents in order to trap ROS formed in the alkaline (due to the addition of slaked lime) chewing mixture within the saliva of a chewer, to scavenge ROS within mucosal cells exposed to an array of tobacco- or areca nut-related carcinogens or tumour promoters, and to inhibit the action of ROS released from ROS-generating white cells during lymphocytic infiltration of the oral mucosa at a precancerous stage. The remission of oral leukoplakias following the administration of vitamin A (200,000 IU/week) or vitamin A (100,000 IU/week) plus beta-carotene (180 mg/week) for 6 months, the inhibition of new leukoplakias during this trial period, and the reduction of micronucleated oral mucosal cells in chewers treated with beta-carotene or vitamin A are indeed promising results. However, a better understanding of the role of ROS in various stages of carcinogenesis will provide the basis for selection of the proper chemopreventive agents and the design of a treatment regime which may either prevent the formation of precancerous lesions, induce their remission, or inhibit the progression of precancerous lesions into malignant cancers.

Certain laboratory hybrid Xiphophorus fish develop heritable neoplasia. Neoplasia can also be induced in some hybrids by treatment with carcinogens. In either case the neoplasms are mediated by a "tumor gene," that is normally controlled by linked or nonlinked "regulating genes" or both. Light and electron microscopic studies on these two types of tumors reveal important differences. The heritable tumor is a compact mass of tissue formed of densely packed melanized melanocytes often with nuclear pockets and projections. A large number of cells undergoing a process of nuclear fragmentation has been observed. The induced tumors, on the other hand, contain fewer melanized melanocytes and show a comparative increase in the amount of connective tissue. The nuclear pockets and projections commonly found in the melanocytes of the heritable tumors are not present in the melanocytes of the induced melanoma. The most important difference observed was the presence of different types of structural chromosome aberrations in the induced tumor and a total absence in the heritable ones. These anomalies seem to be epiphenomenal, and the real genetic change is subchromosomal.

SYNOPSIS. Xiphophorus maculatus (platyfish) exhibits spots which consist of neoplastically transformed pigment cells (T-cells). The spots actually represent extreme benign melanomas. Transformation to T-cells is mediated by a “tumor gene” ( Tu ). Platyfish which develop from X-irradiated embryos reveal an increase of Tu -expression resulting in an overproduction of T-cells to benign melanomas which can be compared to that observed in certain hybrids between the platyfish and Xiphophorus helleri (swordtail). Both the X irradiation-induced and the crossing conditioned increase of Tu -expression represent a heritable alteration which might be related to a conversion from dispersed to condensed chromatin in the interphase nuclei.

5-Bromodeoxyuridine (BrdUrd) injected into the muscular tissue of fish bearing melanoma or neuroblastoma induces the production of virus-like particles in these tumors. The particles in the melanoma are morphologically similar to papovaviruses of polyoma-type, those in the neuroblastoma resemble oncornavirouses of B- and C-type.

1. 1. Certain interspecific hybrids of Xiphophorus segregate in Mendalian ratios into red and orange fish. Their coloration is due to carotenoids and pteridines in the skin. The main carotenoid compounds were identified as two keto-carotenoids, two isomers of zeaxanthin, zeaxanthin, lutein and β-carotene and the main pteridine compounds as neodrosopterin, drosopterin, isodrosopterin, sepiapterin, isoxanthopterin, ranachrome-3 and biopterin. 2. 2. The carotenoids form a yellow background upon which the red and orange coloration are caused by neodrosopterin, drosopterin, isodrosopterin and sepiapterin, depending on their quantities. 3. 3. The red coloration is apparently dependent on a gene which intensifies pigment cell differentiation, whereas the orange coloration presumably is determined by the lack of this gene.

1. 1. The Xiphophorus melanoma system is one of the few well established and genetically well understood in vivo models in experimental carcinogenesis. However, data describing features of intermediary metabolism of the genetically caused melanoma or the different inducible neoplasia, as well as that of the different transformed cell lines of Xiphophorus , are still lacking. For this reason we initiated a comparative study of enolase-, pyruvate kinase-, lactate dehydrogenase- and malate dehydrogenase-activities and pyruvate and lactate levels in transformed as well as normal tissues of Xiphophorus . 2. 2. We observed tissue specific and age dependent activities of the different enzymes and substrate levels. 3. 3. Enzyme activities and substrate levels from all tumors analyzed differ from that of any normal tissue. They are dependent on the tumor sections analyzed, the histiotype and the etiology of the tumors. 4. 4. Analysis of enzyme activities from different in vitro cultured fish cell lines and the human Hela cell line revealed dependency of the intermediary metabolism on oxygen supply, on the proliferative state of the cells and on the cell types. 5. 5. We could not find a correlation between our data and the expression of the c- src gene of Xiphophorus and no genotype-dependent changes in enzyme activities were detected.

Beim wildenPlatypoecilus maculatus aus Mexiko, der im mannlichen Geschlecht heterogamet ist (Gordon 1946), ist neben dem gonosomalen noch ein autosomales System von Geschlechtsrealisatoren am Werke (vgl.Oktay 1959). Es vermag in extremen Konstellationen, die zufalls- oder selektionsbedingt sein konnen, denXY-Mechanismus epistatisch zu uberlagern, so da\XY-Individuen zu ♀♀ determiniert werden konnen.XY-♀♀ sind voll vital und fertil und ergeben in Paarungen mitXY-♂♂ nebenXX-♀♀ undXY-♂♂ voll vitale und fertileXY-♂♂. Auf Grund der vorliegenden Kreuzungsergebnisse und der Befunde anderer Autoren wird angenommen, das der normalerweise rein gonosomale Geschlechtsbestimmungsmodus vonPlatypoecilus maculatus aus dem primitiveren autosomal polyfaktoriellen, der unter anderem bei einem nahen Verwandten dieser Art,Xiphophorus helleri, vorkommt (Kosswig 1931 ff.), hervorgegangen ist.

If certain hybrids ofPlatypoecilus maculatus andXiphophorus helleri (viviparous platyfish and swordtails) are cultivated in diluted sea-water (0.25 or 0.5% salt concentration), the amount of free amino acids increases and the growth of macromelanophores, which normally only form certain black spots at the dorsal fin, is accelerated. Therefore melanomas arise. After changing salt water for fresh water, growth of macromelanophores remains accelerated. The same effect is seen in progenies which have been in an oocytic or embryonic state, when their mother was cultivated for some weeks in diluted sea-water (Figures 1 and 2). A similar effect has been observed in plant galls produced byPhylloxera (Viteus vitifolii) in the genusVitis. When the parasite, which injects amino acids into the tissue of the host in order to produce galls, is removed, gall formation goes on slowly for some days. It is shown that a few hours after injection of amino acids—before formation of neoplasms begins—the concentration of ribonucleic acids is increased. RNS-(and therefore protein-)biosynthesis in neoplasms may be dependent on concentration of free amino acids. A simple concept for the formation of neoplasms in hybrids of platyfish and galls ofPhylloxera is discussed.

A genetic marker, the tumor gene Tu, which causes the formation of abnormal melanophores, the T-melanophores, in the skin of Xiphophorine fish has been transferred by donor DNA from a Tu genotype to recipient embryos lacking Tu. Abnormal melanophores which are identical to the T-melanophores of the donor genotype occurred only in recipients treated with Tu-DNA and not in those treated with Tu-free control DNA.

Rontgenbestrahlung von Embryonen und Keimzellen bestimmter Zahnkarpfen-Genotypen, deren Makromelanophorenproduktion durch Kontrollgene auf die Bildung kleiner Flecken begrenzt ist, verursacht bei heranwachsenden Tieren und deren Nachkommen Pramelanome. Demgegenuber hat die gleiche Behandlung dieser Entwicklungsstadien bei Genotypen, deren Makromelanophorenproduktion infolge Fehlens der Kontrollgene im Verlaufe des weiteren Lebens zur Melanombildung fuhrt, keinen Effekt. Bestrahlung der melanomtragenden Adulten dieses Genotyps verursacht eine vorubergehende Unterbrechung des Tumorwachstums.

1. 1. Premelanomas and melanomas conditioned by the locus Sd on the dorsal fin of Xiphophorin fish showed a several-fold increase in the total LDH activity as compared to the normal counterpart fins. 2. 2. Electrophoretic studies revealed that only B4-isozyme was prominently present in the normal fins, as well as in the premelanomas and the melanomas. 3. 3. The elevated total LDH levels in the premelanomas and the melanomas, as compared to the normal fin, therefore, would appear to represent a higher level of the B4-isozyme.

The particular suitability of the Xiphophorine fish system for achieving genetic transformation is presented, and it was analyzed whether information carrying donor DNA might be available to the propigment cells of embryos of Xiphosphorus helleri, which are the target cells for the transformation. Heterologous 2H3H-labelled donor DNA from E. coli, which was taken for technical reasons instead of homologous fish DNA, undergoes degradation both after injection into the neural crest region and after injection into the yolk sac (molecular weight at O h: 50 X10(6); at 2 h: 1 X 10(6); at 5 h: less than 3 X 10(5); at 10 h: less than 1 X 10(4)). It is concluded therefore, that informative donor DNA is present for about 2 to 3 hours after injection. The DNA of the recipient embryo is labelled radioactively during that time at which informative DNA is present only, if the donor DNA is injected into the neural crest region. The probability that a foreign gene might become available to the propigment cells and might induce transformation is discussed.

Xiphophorus, including swordtails and platyfish, is a genus of small viviparous freshwater fish from Central America that serves increasingly as a laboratory animal [1]. For 25 years we have used Xiphophorus for studies on neoplasia, which can easily be induced in hybrids between descendants of different provenance [2]. Although neoplasia of these animals is rather well understood in terms of formal genetics, the molecular basis of this phenomenon was extremely resistant to any elucidation. Recently a promising approach to the study of neoplasia in Xiphophorus at the molecular level, has been undertaken in a co-operative work of the laboratories of H. Bauer (Institut fur Virologie, Giessen), W. and H. Kersten (Institut fur Physiologische Chemie, Erlangen), S. Nishimura (National Cancer Center Research Institute, Tokyo), and our laboratories. The present review will trace some steps of our studies that led to the detection of a cellular oncogene and a prominent regulatory gene.

Many microbial (Ames et al., 1973; Nagao and Sugimura, 1972) as well as other sub-mammalian (e.g., Neurospora: Ong and de Serres, 1972; Yeast: Koske and Stich, 1973) and mammalian (Stich and San, 1970; Stich et al., 1971, 1976) cell systems for the detection of potential carcinogens have been developed and successfully applied. They are economic and time-saving as compared to the systems consisting of entire test animals such as laboratory mice, rats, and others. However, one should keep in mind that the feasibility of these cell systems suffers from a certain ambiguity in relating the in vitro effects (e.g., mutation, numerical and structural chromosome aberrations, sister chromatid exchanges, focus-forming capacity, etc.) to the in vivo event of neoplastic transformation in the entire animal. In vitro cell test systems, therefore, cannot satisfactorily replace in vivo test systems.

The concept of genes that code for neoplastic transformation, called “oncogenes” today, originates from two sources: from virology and from animal genetics. The virological source can be traced back to the year 1911 when Peyton Rous discovered the virus that causes sarcoma in chickens. It took, however, about sixty years until evidence was brought about that the cancer determinants located in the genome of this virus and of related viruses (retroviruses) are genes (Huebner and Todaro, 1969; Bentvelzen, 1972). The source that originates from animal genetics can be traced back to the year 1928 when Myron Gordon, Georg Haussler, and Curt Kosswig indepently discovered that the F1 hybrids between certain domesticated ornamental breeds of the Central American fish species Xiphophorus maculatus (platyfish) and Xiphophorus helleri (swordtail) spontaneously develop melanoma that is inherited in the hybrid generations like the phenotype of any normal Mendelian gene located in the genome of the fish. Both, Rous’ sarcoma virus (RSV) and Xiphophorus fish represent up to date highly suitable models for research on oncogenes.

Elektrophoretische Untersuchungen an benignen und malignen Ruckenflossenmelanomen sowie an normalen Ruckenflossen lebendgebarender Zahnkarpfen zeigen, dass in den Geweben in erster Linie die fur gut mit Sauerstoff versorgtes Gewebe typische Herz-LDH (B4-Isoenzym) vorkommt. Die fur schlecht mit Sauerstoff versorgtes Gewebe typische Muskel-LDH (A4-Isoenzym) wird nur in manchen der untersuchten Gewebe gefunden, und ist auch dort nur in sehr geringer Menge vorhanden. Die Melanome scheinen also im Gegensatz zu vielen anderen Neoplasmen anderer Systeme aeroben Stoffwechsel durchzufuhren.

Linkage between an autosomal regulatory gene Diff controlling differentiation of neoplastic melanophores and an esterase locus, Est-1, has been demonstrated in Xiphophorus. The recombination values between Est-1 and Diff ranged from 21 to 29 percent depending on the melanophore pattern loci Sp, Sd, Sd, and Livar. The average recombination frequency for all genotypes investigated was 25 percent. Since Est-1 and Diff do not assort independently of each other, it is concluded that Est-1 and Diff are both located on the same chromosome. Thus, the Est-1 locus provides a marker for monitoring the presence of the Diff autosome.

Specific genotypes of the xiphophorine fish develop neoplasms following treatment with N-methyl-N-nitrosourea or X-rays. Several of these neoplasms can be related to the presence of specific chromosomes. The implications of these findings are discussed.

Currently in cancer research much emphasis is being placed on mutation [2–4], rearrangement [5], amplification [6–8], and demethylation [9] of oncogenes that are supposed to represent the primary events leading to oncogene activation when carcinogens trigger neoplasia in animals or humans (the reader is referred to ref. [10] for more extensive details on this topic). The data underlying this supposition were mainly derived from experiments performed with tumor cells in vitro. In vivo studies on this issue are rare.

Explants from genetically determined melanotic and amelanotic melanomas of platyfish-swordtail hybrids were cultivated in H3-thymidine-containing medium with or without additional amounts of amino acids. The incorporation of label into the DNA extracted from the explants was measured, and the DNA content per unit protein was determined. The results revealed a significant difference between the two melanoma types; the rate of DNA synthesis as well as the DNA to protein ratio of amelanotic melanoma explants was about twice that of melanotic ones. This is consistent with the results of earlier investigations which had shown that the amelanotic melanomas grow more rapidly and contain more incompletely differentiated cells than the melanotic ones. The data, furthermore, demonstrated that both melanoma types exhibit extreme individual variations in DNA synthesis and in the DNA to protein ratio. The present study failed to confirm the results of earlier autoradiographic studies which suggested that additional amounts of amino acids in the culture medium stimulate the incorporation of labeled thymidine into the melanoma DNA. The results of the present experiments on melanomas in vitro do not rule out the possibility that amino acids stimulate melanoma growth in vivo by initiating DNA synthesis and cell division of melanoma cells.

Publisher Summary Oncogenes are genes that code for neoplastic transformation and possibly for the maintenance of the neoplastic state of a cell. This chapter unifies populational, morphological, developmental, and cell biological findings obtained during research on the biology of the oncogene Tu of Xiphophorus. In addition, it shows that neoplasia of multicellular animals including human's results from the elimination, deletion, impairment, or insufficicncy of regulatory genes that normally control the oncogene, or from the introduction of uncontrolled accessory oncogenes into the genome. The Xiphophorus tumor system has provided the opportunity to reduce the enormous complexity of cancer etiology to a few biological elements basically involved in neoplasia. The development of a tumor requires an oncogene that after impairment, deletion, or elimination of its regulatory genes is permitted to mediate neoplastic transformation. Emphasis is being placed today in cancer research on the actual oncogenes themselves, but, the most important genes involved in neoplasia are these regulatory genes. However, although detected by classical genetics in the Xiphophorus system, these genes are not at present open to a more finely detailed molecular biological analysis. Their actual mode of action is, therefore, still far from being understood.

Tissue-specific esterases of the xiphophorine fishes Platypoecilus maculatus (platyfish), Xiphophorus helleri (swordtail), and their F1 hybrid have been analyzed using disc electrophoresis. Seven esterase zones (resolved into a maximum of nine bands) exist in these fishes, and these have been classified by employing specific inhibitors. Five of the seven zones, EST-1, EST-2, EST-5, EST-6, and EST-7, appeared to be carboxylesterases; while the two remaining zones, EST-3 and EST-4, were classified as cholinesterases. In the liver of the platfish, all seven esterase zones were detected, while the liver of the swordtail exhibited only five esterase zones. EST-1 and EST-3 were lacking in the liver tissue of the swordtail. All seven esterase loci were expressed in the liver tissue of the F1 hybrid. The reciprocal crosses gave the same results. In the fin, skin, skeletal muscle, and eye tissues from all three genotypes, three major esterase zones, EST-2, EST-5, and EST-7, were detected. In addition, EST-1 was frequently detected in all these tissues of the platfish and the F1, but was lacking in the swordtail. Serum from three genotypes showed one prominent esterase zone, EST-5; however, trace activity of EST-2 and EST-7 zones could also be detected. It seems that in all tissues of the F1 hybrid there is expression of all the esterase genes from the platfish. The results of the present study are discussed in the comparison to those from other studies on teleost esterases.

In the genetically determined pigment cell tumors of platyfish and platyfish-swordtail hybrids, the degree of malignancy of pigment cells which have been neoplastically transformed by a tumor gene (Tu) depends on the type and number of certain regulating genes (R). In the present study, the tyrosinase activities in tumors of different degrees of malignancy (black spots, premelanomas, melanomas) have been determined. The results demonstrate a close correlation between the level of tyrosinase activity and the degree of malignancy. Spot patterns consisting of completely differentiated (benign) Tu-transformed cells show no tyrosinase activity. Premelanomas containing a few incompletely differentiated (malignant) Tu-transformed cells in addition to many differentiated ones show moderate tyrosinase activities. Melanomas which contain increasing numbers of incompletely differentiated cells with increasing growth rates show high to extremely high tyrosinase activities. Thus, the tyrosinase levels present in these tumors can be used as an indicator for the degree of differentiation and, thereby, for the degree of malignancy of the neoplastically transformed pigment cells.

Karyotypic changes involving a deletion and a translocation of certain sex-linked tumor-inducing loci of the platyfish, Platypoecilus (Xiphophorus) maculatus, have been investigated. The effects of these chromosome aberrations on tumor formation and viability of the fish are discussed.

1. 1. A comparative study of substances fluorescing at 365 nm found in the skin and fins of Xiphophorine fish was carried out by means of thin-layer chromatography and fluorometry. Groups of single xanthophores, xanthoerythrophores and melanophores were examined by means of micro cellulose thin layers. 2. 2. Fifteen spots could be found in thin-layer chromatographs. Nine compounds were identified as pteridines, five remained unknown, but may also be pteridines while one is riboflavin. 3. 3. The macropterinophore pattern controlled by the locus Dr (= dorsal red) and the macromelanophore pattern of Sd (= spotted dorsal) were investigated with regard to their pteridine content in four purebred strains and six hybrid genotypes. While some genotypes contain only the colourless pteridines: isoxanthopterin, ranachrome-3 and biopterin (“limited” pattern); others additionally possess the coloured pteridines: neodrosopterin, drosopterin, isodrosopterin and sepiapterin (“complete” pattern). 4. 4. The amounts of pteridines found depend on both the types and the numbers of chromatophores.

The concept of genes that code for neoplastic transformation, called “oncogenes,” originates from two sources, virology and animal genetics. The virological source can be traced back to the year 1910 when Peyton Rous discovered the virus that causes sarcoma in chickens. It took, however, about 60 years until evidence was produced that the cancer determinants located in the genome of this and related viruses (retroviruses) are truly genes [1, 2]. The source in animal genetics dates from 1929, when Myron Gordon, Georg Haussler, and Curt Kosswig independently discovered that the F1 hybrids between certain domesticated ornamental breeds of the Central American fish species Xiphophorus maculatus (platyfish) and X. helleri (swordtail) spontaneously develop melanoma that is inherited in the hybrid generations like the phenotype of any normal Mendelian gene located in the genome of the fish.

Nach abrupter uberfuhrung von Zahnkarpfen aus Susswasser in verdunntes Meerwasser schwingt sich der Pool der sogenannten freien Aminosauren von einem ursprunglichen auf einen neuen erhohten stationaren Zustand ein. Ein ganz entsprechendes Zeitverhalten hat der H3-Thymidin-Markierungsindex (Anzahl markierter Kerne/Gesamtkernzahl) in Melanomen von Bastarden, deren Farbzellen genetisch total dereprimiert sind.

Bei bestimmten Zahnkarpfen-Bastarden treten stets erbbedingte Melanome auf. Diese entstehen dadurch, dass bestimmte Gene, die fur die Differenzierung von Farbzellen verantwortlich sind, enthemmt und gleichzeitig zu einer gesteigerten Aktivitat angeregt werden. Die Enthemmung beruht auf einem Verlust bestimmter Repressionsgene und die Aktivitatssteigerung auf einer Einfuhrung polyfaktorieller Systeme von Induktionsgene. Es bestehen schwerwiegende Indizien dafur, dass die Induktorsubstanzen mit Aminosauren identisch sind.

The Xiphophorin fish, including platyfish and swordtails, live in brooks, rivers, ponds and pools in Central America, where they have developed many species, subspecies, and populations. In some populations nearly all individuals have certain spot patterns composed of macromelanophores, in others only a certain percentage of the individuals are spotted, then again others exhibit no spots whatsoever (Gordon, 1942, 1947; Gordon and Gordon, 1950, 1957; Kallman, personal communication). Such spot patterns are, without a doubt, phylogenetic late acquirements which succeed in overcoming ecological and geographical barriers from population to population, and species to species.

H3-DNA vonSalmonella typhimurium wurde in den Dotter vonPlatypoecilus maculatus-Embryonen injiziert und ihr Verbleib untersucht. Nach 45 Stunden findet man 45% der injizierten H3-DNA-Radioaktivitat in der saureloslichen Fraktion des Dotters. Von diesem Zeitpunkt an nimmt die Radioaktivitat in der saureunloslichen Fraktion der Embryonen standig zu, bis nach 140 Stunden ein Wert von 50% erreicht ist. Der hohe Anteil an radioaktivem saurenunloslichem Material im Dotter, der 140 Stunden nach der Injektion noch ca. 35% betragt, lasst vermuten, dass hier noch hochmolekulare Bakterien-DNA vorhanden ist. Somit erscheint die Moglichkeit einer Aufnahme dieser hochmolekularen DNA in die Embryozellen nicht ausgeschlossen.

BeiP. maculatus werdenXY-Embryonen durch Rontgenstrahlenbehandlung (1000 bis 2500 R) physiologisch zu normalen Weibchen umdeterminiert.