The germline-restricted chromosome (GRC) of songbirds represents a taxonomically widespread example of programmed DNA elimination. Despite its apparent indispensability, we still know very little about the GRC's genetic composition, function, and evolutionary significance. Here we assemble the GRC in two closely related species, the common and thrush nightingale. In total we identify 192 genes across the two GRCs, with many of them present in multiple copies. Interestingly, the GRC appears to be under little selective pressure, with the genetic content differing dramatically between the two species and many GRC genes appearing to be pseudogenized fragments. Only one gene, cpeb1, has a complete coding region in all examined individuals of the two species and shows no copy number variation. The acquisition of this gene by the GRC corresponds with the earliest estimates of the GRC origin, making it a good candidate for the functional indispensability of the GRC in songbirds.

• MeSH
• biologická evoluce MeSH
• chromozomy MeSH
• otevřené čtecí rámce MeSH
• zárodečné buňky MeSH
• zpěvní ptáci * genetika   MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

Individual groups of retroviruses and retroviral vectors differ in their integration site preference and interaction with the host genome. Hence, immediately after infection genome-wide distribution of integrated proviruses is non-random. During long-term in vitro or persistent in vivo infection, the genomic position and chromatin environment of the provirus affects its transcriptional activity. Thus, a selection of long-term stably expressed proviruses and elimination of proviruses, which have been gradually silenced by epigenetic mechanisms, helps in the identification of genomic compartments permissive for proviral transcription. We compare here the extent and time course of provirus silencing in single cell clones of the K562 human myeloid lymphoblastoma cell line that have been infected with retroviral reporter vectors derived from avian sarcoma/leukosis virus (ASLV), human immunodeficiency virus type 1 (HIV) and murine leukaemia virus (MLV). While MLV proviruses remain transcriptionally active, ASLV proviruses are prone to rapid silencing. The HIV provirus displays gradual silencing only after an extended time period in culture. The analysis of integration sites of long-term stably expressed proviruses shows a strong bias for some genomic features-especially integration close to the transcription start sites of active transcription units. Furthermore, complex analysis of histone modifications enriched at the site of integration points to the accumulation of proviruses of all three groups in gene regulatory segments, particularly close to the enhancer loci. We conclude that the proximity to active regulatory chromatin segments correlates with stable provirus expression in various retroviral species.

• Klíčová slova
• gene regulatory elements, genome-wide provirus distribution, provirus silencing, retrovirus integration,
• MeSH
• aktivace transkripce * MeSH
• Alpharetrovirus genetika   MeSH
• buněčné linie MeSH
• chromatin genetika   MeSH
• epigeneze genetická MeSH
• genetické vektory genetika   MeSH
• genový targeting MeSH
• HIV-1 genetika   MeSH
• integrace viru MeSH
• lidé MeSH
• myši MeSH
• plazmidy genetika   MeSH
• počátek transkripce MeSH
• proviry genetika   MeSH
• regulace exprese virových genů MeSH
• regulační oblasti nukleových kyselin * MeSH
• stabilita RNA MeSH
• umlčování genů MeSH
• virus myší leukemie genetika   MeSH
• zesilovače transkripce MeSH
• zvířata MeSH
• Check Tag
• lidé MeSH
• myši MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• chromatin MeSH

Myeloblastosis-associated virus 2 (MAV-2) is a highly tumorigenic simple avian retrovirus. Chickens infected in ovo with MAV-2 develop tumors in the kidneys, lungs, and liver with a short latency, less than 8 weeks. Here we report the results of molecular analyses of MAV-2-induced liver tumors that fall into three classes: hepatic hemangiosarcomas (HHSs), intrahepatic cholangiocarcinomas (ICCs), and hepatocellular carcinomas (HCCs). Comprehensive inverse PCR-based screening of 92 chicken liver tumors revealed that in ca. 86% of these tumors, MAV-2 provirus had integrated into one of four gene loci: HRAS, EGFR, MET, and RON Insertionally mutated genes correlated with tumor type: HRAS was hit in HHSs, MET in ICCs, RON mostly in ICCs, and EGFR mostly in HCCs. The provirus insertions led to the overexpression of the affected genes and, in the case of EGFR and RON, also to the truncation of exons encoding the extracellular ligand-binding domains of these transmembrane receptors. The structures of truncated EGFR and RON closely mimic the structures of oncogenic variants of these genes frequently found in human tumors (EGFRvIII and sfRON).IMPORTANCE These data describe the mechanisms of oncogenesis induced in chickens by the MAV-2 retrovirus. They also show that molecular processes converting cellular regulatory genes to cancer genes may be remarkably similar in chickens and humans. We suggest that the MAV-2 retrovirus-based model can complement experiments performed using mouse models and provide data that could translate to human medicine.

• Klíčová slova
• avian retroviruses, insertional mutagenesis, retroviral oncogenesis,
• MeSH
• cholangiokarcinom genetika   virologie   MeSH
• geny erbB-1 * MeSH
• hemangiosarkom genetika   virologie   MeSH
• hepatocelulární karcinom genetika   virologie   MeSH
• integrace viru MeSH
• inzerční mutageneze * MeSH
• karcinogeneze * MeSH
• kur domácí genetika   MeSH
• lidé MeSH
• nádory jater genetika   virologie   MeSH
• onkogeny MeSH
• protoonkogenní proteiny c-met genetika   MeSH
• proviry genetika   fyziologie   MeSH
• ptačí proteiny genetika   MeSH
• tyrosinkinasové receptory genetika   MeSH
• virus ptačí myeloblastózy genetika   fyziologie   MeSH
• zvířata MeSH
• Check Tag
• lidé MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• protoonkogenní proteiny c-met MeSH
• ptačí proteiny MeSH
• RON protein MeSH Prohlížeč
• tyrosinkinasové receptory MeSH

Retroviruses and retrovirus-derived vectors integrate nonrandomly into the genomes of host cells with specific preferences for transcribed genes, gene-rich regions, and CpG islands. However, the genomic features that influence the transcriptional activities of integrated retroviruses or retroviral vectors are poorly understood. We report here the cloning and characterization of avian sarcoma virus integration sites from chicken tumors. Growing progressively, dependent on high and stable expression of the transduced v-src oncogene, these tumors represent clonal expansions of cells bearing transcriptionally active replication-defective proviruses. Therefore, integration sites in our study distinguished genomic loci favorable for the expression of integrated retroviruses and gene transfer vectors. Analysis of integration sites from avian sarcoma virus-induced tumors showed strikingly nonrandom distribution, with proviruses found prevalently within or close to transcription units, particularly in genes broadly expressed in multiple tissues but not in tissue-specifically expressed genes. We infer that proviruses integrated in these genomic areas efficiently avoid transcriptional silencing and remain active for a long time during the growth of tumors. Defining the differences between unselected retroviral integration sites and sites selected for long-terminal-repeat-driven gene expression is relevant for retrovirus-mediated gene transfer and has ramifications for gene therapy.

• MeSH
• chromozomy virologie   MeSH
• exprese genu MeSH
• genetická terapie metody   MeSH
• genetické vektory MeSH
• integrace viru * MeSH
• kur domácí MeSH
• proviry genetika   fyziologie   MeSH
• ptačí sarkom virologie   MeSH
• viry ptačího sarkomu genetika   fyziologie   MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH