RESUMO
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.
Assuntos
Cromossomos , Doenças dos Peixes/genética , Melanoma/veterinária , Animais , Doenças dos Peixes/patologia , Melanoma/genética , Melanoma/patologia , Oncogenes , PoeciliaRESUMO
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.
Assuntos
Albinismo/genética , Monofenol Mono-Oxigenase/genética , Mutação , Oryzias/genética , Animais , Animais Geneticamente Modificados , Southern Blotting , Embrião não Mamífero , Feminino , Masculino , Melaninas/metabolismo , Camundongos , Monofenol Mono-Oxigenase/metabolismo , Oryzias/embriologia , Fenótipo , Distribuição Tecidual , TransgenesRESUMO
Spontaneous melanoma in hybrids of Xiphophorus is caused by overexpression of the receptor tyrosine kinase gene Xmrk. In rare cases melanoma also occurs in non-hybrid fish from natural habitats where the trigger is unknown. In these tumors Xmrk is overexpressed too, pointing to a similar molecular mechanism underlying neoplastic transformation. After carcinogen treatment a variety of tumor of other histiotypes are induced. Tumor genes other than Xmrk seem to cause these neoplasias. Genetic alterations have been detected in a recently isolated mutant, and immunomodulators, and androgens can cause regression of hybrid melanoma. The variety of etiologies and the multiplicity of exogenous factors and agents that induce cancer or modify the neoplastic phenotype allow the study in Xiphophorus of many of the problems of tumorigenesis found in vivo.
Assuntos
Ciprinodontiformes/genética , Modelos Animais de Doenças , Regulação Neoplásica da Expressão Gênica/genética , Melanoma/genética , Animais , Carcinógenos/farmacologia , Quimera/genética , Ciprinodontiformes/metabolismo , Relação Dose-Resposta a Droga , Genótipo , Melanoma/etiologia , Melanoma/metabolismo , Mutagênese , Oncogenes/genética , Remissão Espontânea , Esteroides/farmacologiaRESUMO
Melanoma in hybrids of Xiphophorus is due to the unrestricted activity of a cellular oncogene locus, Tu, encoding the growth factor receptor gene Xmrk. In nonhybrid parental fish, Tu is controlled by a tumor suppressor gene. Thus, its restricted activity leads there only to a nonmalignant, species- and population-specific macromelanophore spot pattern. Prompted by enigmatic reports on nonhybrid Xiphophorus with pigmentation abnormalities resembling melanoma, we have studied pigmentation in descendants of wild-caught fish and purebred laboratory stocks derived from wild populations. Whereas most stocks exhibiting macromelanophore patterns never developed pigmentation abnormalities, an exceptional situation for some nonhybrids was found. In X. variatus carrying the macromelanophore pattern "punctatus-2" and in X. cortezi with "spotted caudal," expressivity of the pigmentation gene ranges from a few black spots to extreme melanosis and eventually to malignant melanoma. In X. maculatus with the mutant pigmentation gene striped" carrying in addition the micromelanophore pattern "anal fin black" or "lower comet," testosterone-dependent melanoma develop originating from the corresponding micromelanophore pattern. The tumors are highly malignant and express a melanoma-associated antigen. Overexpression of the Xmrk oncogene appears as the underlying molecular mechanism for tumor induction. These findings clearly demonstrate that tumors can also develop in purebred wild-type fish. The classical model for formation of hereditary melanoma in Xiphophorus hybrids does not explain the development of melanoma in the absence of hybridization. However, their existence gives additional support to the reasoning that the Xmrk oncogene associated with the macromelanophore locus is potentially injurious.
Assuntos
Ciprinodontiformes/genética , Melanoma/genética , Oncogenes , Animais , Antígenos de Neoplasias , Hibridização Genética , Melanoma/etiologia , Melanoma/imunologia , Melanoma/patologia , Melanoma/veterinária , Melanóforos/ultraestrutura , PigmentaçãoRESUMO
Melanoma formation in platyfish/swordtail hybrids of genus Xiphophorus is due to overexpression of the receptor tyrosine kinase oncogene Xmrk. This gene is the molecular equivalent to the Tu-locus of platyfish formerly identified by Mendelian genetics. The supposed evolutionary origin of the Xmrk oncogene is a nonhomologous recombination event in the 5' region of the corresponding Xmrk protooncogene with an anonymous sequence, D. This event led to a gene duplication of Xmrk, whereby the new copy obtained a novel promoter derived from D. Inactivity of this promoter in parental fish warrants lack of tumorigenicity of the Xmrk oncogene in wild playfish. In hybrids, however, the promoter is active. This leads to the pigment cell transforming overexpression of Xmrk.
Assuntos
Evolução Biológica , Ciprinodontiformes/genética , Doenças dos Peixes/genética , Proteínas de Peixes , Melanoma/veterinária , Oncogenes , Receptores Proteína Tirosina Quinases/genética , Células 3T3 , Animais , Animais Geneticamente Modificados , Ciprinodontiformes/classificação , Feminino , Regulação Neoplásica da Expressão Gênica , Hibridização Genética , Masculino , Melanoma/genética , Melanóforos , Camundongos , Modelos Genéticos , Fosforilação , Regiões Promotoras Genéticas , Processamento de Proteína Pós-Traducional , Proto-Oncogenes , Proteínas Recombinantes de Fusão/metabolismo , Recombinação GenéticaRESUMO
Hereditary melanoma in Xiphophorus hybrids carrying the melanoma-inducing Tu-Sd locus is caused by transcriptional activation of the Xmrk gene that resides at the Tu-Sd locus and encodes a novel member of receptor tyrosine kinases (RTK). In this study, a total of 27 hereditary melanomas from various hybrid genotypes harbouring 7 different Tu alleles were also found to over-express the corresponding Xmrk alleles. The level of over-expression correlated with the degree of malignancy of the melanoma. In addition, Xsrc expression was high in many malignant melanomas. Expression patterns and levels of the Xiphophorus EGF-receptor gene (Xerb B), the c-myc (Xmyc), and the PDGF (Xsis) gene(s) were not intriguing. Transcription of the ras gene(s) may be correlated to secondary events of melanoma progression. Expression patterns of Xfms, the Xiphophorus CSF-I receptor homologue, can be explained by different contents of infiltrating macrophages in the tumors. In carcinogen-induced tumors including one melanoma no significant expression of the Xmrk oncogene could be detected. Xsrc expression, however, was strikingly high. This indicates that activation of oncogenes other than Xmrk is instrumental in tumorigenesis of neoplasia of non-hereditary origin.
Assuntos
Ciprinodontiformes , Fibrossarcoma/genética , Proteínas de Peixes , Melanoma/genética , Oncogenes/genética , Proto-Oncogenes/genética , Receptores Proteína Tirosina Quinases , Animais , Northern Blotting , Expressão Gênica , Proteínas Tirosina Quinases/genética , Transcrição Gênica , Cromossomo X , Cromossomo YRESUMO
In clonal unisexual vertebrates, the genes specifying the males become dispensable. To study the fate of such genes the gynogenetic all-female fish Poecilia formosa was treated with androgens. Phenotypic males were obtained that exhibited the complete set of male characteristics of closely related gonochoristic species, including body proportions, pigmentation, the extremely complex insemination apparatus of poeciliid fish, sexual behavior, and spermatogenesis. The apparent stability of such genic structures, including those involved in androgen regulation, is contrasted by high instability of noncoding sequences. Frequent mutations, their clonal transmission, and at least two truly hypervariable loci leading to individual differences between these otherwise clonal organisms were detected by DNA fingerprinting. These observations substantiate the concept that also in "ameiotic" vertebrates certain compartments of the genome are more prone to mutational alterations than others.
RESUMO
A method was developed to investigate in vitro metabolism of human trabecular bone and its hormonal regulation. Human and bovine parathyroid hormone 1-34 caused an increase in the release of calcium and magnesium out of human bone. Human, salmon and porcine calcitonin caused a decrease in the release of calcium and magnesium and inhibited the effect of parathyroid hormone.
Assuntos
Osso e Ossos/enzimologia , Calcitonina/fisiologia , Eletrólitos/metabolismo , Metabolismo Energético , Hormônio Paratireóideo/fisiologia , Idoso , Fosfatase Alcalina/metabolismo , Cálcio/metabolismo , Feminino , Cabeça do Fêmur/enzimologia , Humanos , Hidroxiprolina/metabolismo , Magnésio/metabolismo , Masculino , Pessoa de Meia-Idade , Osteoartrite/enzimologia , Fosfatos/metabolismoRESUMO
A procedure was developed to investigate the electrolyte metabolism of human trabecular bone and its regulation in vitro, in particular the influence of prostaglandins. Trabecular bone was prepared from femoral heads of patients who had undergone hip replacement surgery for coxarthrosis. 500 mg samples were incubated in modified EAGLE's minimal essential medium. Net electrolyte movements between bone and incubation medium were measured. During 6 hours of incubation PGE2 caused an increase in the release of calcium and magnesium from bone into incubation medium as compared to controls. The effect of PGE2 was dose-dependent and comparable to that of human parathyroid hormone 1-34 (hPTH 1-34) whereas hPTH 3-34 had no effect. Human calcitonin (hCT) caused a decrease in the release of calcium and magnesium. PGE2 was found to be the most potent prostaglandin. PGE1 and PGF2 alpha had about 50% and PGF1 alpha about 40% of the potency of PGE2. PGA1 and PGA2 had no effect. The effect of PGE2 could be completely inhibited by hCT and was not further enhanced by hPTH 1-34. Magnesium movement was affected in the same way as calcium movement, while phosphate movement and release of alkaline phosphatase and hydroxyproline from bone into incubation medium were not affected by prostaglandins.
Assuntos
Osso e Ossos/metabolismo , Eletrólitos/metabolismo , Prostaglandinas/farmacologia , Idoso , Alprostadil , Osso e Ossos/efeitos dos fármacos , Calcitonina/farmacologia , Cálcio/metabolismo , Dinoprosta , Dinoprostona , Relação Dose-Resposta a Droga , Humanos , Técnicas In Vitro , Pessoa de Meia-Idade , Hormônio Paratireóideo/farmacologia , Prostaglandinas A/farmacologia , Prostaglandinas E/farmacologia , Prostaglandinas F/farmacologiaRESUMO
Prostaglandins seem to be involved in the pathogenesis of juxtaarticular osteopenia in rheumatoid arthritis. Therefore the influence of prostaglandins on in vitro electrolyte metabolism of human trabecular bone was tested. Trabecular bone was prepared from femoral heads of patients who had undergone hip replacement surgery for coxarthrosis. 500 mg samples of trabecular bone were incubated in modified Eagle's minimal essential medium. Net electrolyte movements between bone and incubation medium were measured. PGE2 caused an increase in the release of calcium (Ca) and magnesium (Mg) from bone into incubation medium as compared to controls (PGE2 1 micrograms/ml: Ca = 0.87 +/- 0.09 mmol/l*, Mg = 0.44 +/- 0.03 mmol/l*; controls: Ca = 0.81 +/- 0.09 mmol/l, Mg = 0.41 +/- 0.05 mmol/l; n = 15, *p less than 0.001). The effect of PGE2 was dose-dependent and comparable to the effect of human parathyroid hormone 1-34 (hPTH 1-34). PGE2 turned out to be the most potent prostaglandin on human trabecular bone. PGE1 and PGF2 alpha had about 50% and PGF1 alpha about 40% of the potency of PGE2. PGA1 and PGA2 had no effect. The effect of PGE2 could be completely inhibited by human calcitonin (hCT), similar to the inhibition of the effect of hPTH 1-34 by hCT. The effect of PGE2 was not further enhanced by hPTH 1-34. Magnesium metabolism was affected in all experiments in the same way as calcium metabolism. Phosphate metabolism, release of alkaline phosphatase and hydroxyproline from bone into incubation medium were not affected by prostaglandins.