Annerose Anders

Xiphophorus as an in vivo model for studies on normal and defective control of oncogenes.

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 humans 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.

Regulation of Gene Expression in the Gordon-Kosswig Melanoma System

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.

Genetic basis of susceptibility for development of neoplasms following treatment with N-methyl-N-nitrosourea (MNU) or X-rays in the platyfish/swordtail system

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.

Genetics of susceptibility in the platyfish/swordtail tumor system to develop fibrosarcoma and rhabdomyosarcoma following treatment with N-methyl-N-nitrosourea (MNU)

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.

Effects of X-irradiation on the genetically-determined melanoma system of xiphophorin fish

Röntgenbestrahlung 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 Prämelanome. Demgegenüber hat die gleiche Behandlung dieser Entwicklungsstadien bei Genotypen, deren Makromelanophorenproduktion infolge Fehlens der Kontrollgene im Verlaufe des weiteren Lebens zur Melanombildung führt, keinen Effekt. Bestrahlung der melanomtragenden Adulten dieses Genotyps verursacht eine vorübergehende Unterbrechung des Tumorwachstums.

X ray-induced mutations of the genetically-determined melanoma system of xiphophorin fish

Die nach Röntgenbestrahlung von Embryonen vonPlatypoecilus maculatus auftretende erbliche Überproduktion von Makromelanophoren (Bildung von Prämelanomen) beruht offenbar auf einer Vielzahl von Mutationen eines über alle Chromosomen verteilten Systems von Repressionsgenen, das die für die Makromelanophorenbildung verantwortlichen Gene kontrolliert.

Paragenetic suppressors of suppressor genes – a new class of oncodeterminants

Abstract 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.

The genes that carcinogens act upon.

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.

Search for Genes Critical for the Early and/or Late Events in Carcinogenesis: Studies in Xiphophorus (Pisces, Teleostei)

Southern blot analyses of the xiphophorine genome with probes specific for 15 viral and cellular oncogenes revealed that only three v-erbB related EcoRI fragments comprising 4.9 kb of a certain X, 11.5 kb of another X, and 6.7 kb of both a Y and a Z chromosome are inherited in parallel with the Tu complex and melanoma formation. They are accessory in the genome, and are highly homologous with each other and with an ubiquitous autosomal 7.5-kb fragment. The latter one is probably linked to the indispensable Tu complex that is postulated to be present in all individuals of Xiphophorus irrespective of whether they possess or lack the capacity to form melanoma in interspecific hybrids. Three restriction fragments, the X-chromosomal 4.9-kb, the Y-chromosomal 6.7-kb and the ubiquitous Tu-nonlinked 5.5-kb EcoRI fragments were cloned and sequenced. The X- and the Y-chromosomal fragments show perfect identity in the regions of the putative exons C and D of the EGF receptor gene and minor but significant differences to the putative exon C (exon D not identified) of the Tu-nonlinked fragment of 5.5 kb, indicating that at least two different types of x-erb B genes coding for slightly different EGF-receptors exist in the fish. Northern blot analyses revealed expression of the Tu-linked x-erbB genes (x-gfrB genes) in both transformed and nontransformed tissue, suggesting their essential role in regulation of normal cell proliferation and in carcinogenesis. We conclude that the indispensable x-egfrB genes remain unchanged and strictly regulated, while the sex chromosomal accessory x-egfrB genes possibly undergo dramatic changes in structure and/or function (e.g., unscheduled expression, ectopic expression, point mutations, truncation) leading to activation of the oncogenic potential of these genes, which in turn could induce several cellular events involved in the switch from the normal to the transformed state of the cell. In contrast, none of the x-erbA restriction fragments could be assigned to the Tu-complex or to any regulatory gene (R or S). These results, however, do not exclude the existence of a structural and/or functional relation between x-erbA genes and R and S genes. We therefore analyzed x-erbA genes by cloning, sequencing, and expression studies.(ABSTRACT TRUNCATED AT 400 WORDS)

XY females caused by X-irradiation

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