Histone proteins were examined during development in the meiotic elongate and a genetically close line N6HT. Histones were also extracted from an F1 (el x N6Ht). Comparisonc beteen the histone samples from each line of N6HT and elongate, and the F1 for leaf, root, and stem were inconclusive. A tassel sample form elongate exhibited a markedly slower migrating band that was not present in N6HT. The histone profiles of elongate and N6HT also differed. Each line N6HT and elongate exhibited three protein bands in the H1 region. Maize histone samples have been shown to exhibit four major H1 bands. The possibility exists that an H1 protein altered in its molecular weight and possibly in its interaction with the chromosome is present in elongate.

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Orientador: Silvia Regina Rogatto / Banca: Edigard Graner / Banca: Claudia Aparecida Rainho / Resumo: Os tumores de glândulas salivares (TGS) são lesões raras que apresentam heterogeneidade morfológica e sobreposição histológica entre os vários subtipos de tumores. Neste estudo foi utilizada a técnica de hibridação genômica comparativa de alta resolução (HR-CGH) em 64 amostras de TGS, incluindo: 27 adenomas pleomórficos (AP); 11 tumores de Warthin (TW); seis carcinomas ex-adenomas pleomórficos (CXAP); seis carcinomas adenóides císticos (CAC); quatro carcinomas mucoepidermóides (CME); três carcinomas ductais salivares (CDS); três adenocarcinomas (ACAR); dois oncocitomas (ON) e dois carcinomas epiteliaismioepiteliais (CEM). Destas, 47 amostras eram provenientes de tecidos fixados em formalina e em blocos de parafina (FFEP) e 17 de tecidos a fresco. Após a microdissecção, o DNA genômico foi amplificado e marcado por técnica baseada na PCR (SCOMP) e por nick translation, respectivamente. Os cromossomos foram cariotipados usando a imagem DAPI invertido e a intensidade do sinal de hibridação foi determinada ao longo de cada cromossomo. Uma biblioteca com amostras de DNA normais foi construída para selecionar os limites superiores e inferiores para perdas e ganhos cromossômicos. Em todos os casos, as perdas genômicas foram observadas mais freqüentemente do que os ganhos. Na análise comparativa das regiões mínimas comuns detectadas pela HR-CGH envolvendo todos os tipos tumorais, foram observadas alterações genômicas comuns aos diversos tipos, como também exclusivas para os diferentes tipos histológicos. As regiões genômicas consistentemente alteradas nos dois subgrupos tumorais com maior número amostral (adenomas pleomórficos e tumores de Warthin) foram investigadas em bancos de dados para a seleção de genes candidatos que pudessem estar relacionados com a etiologia destes tumores. Os genes NEDD9 (6p24-p25), PPARG (3p25) e c-MYC (8q24.21) foram... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Salivary gland tumors (SGT) are uncommon lesions showing morphologic heterogeneity and histologic overlap among various tumoral subtypes. In the present study, high resolutioncomparative genomic hybridization (HR-CGH) method was performed in 64 SGT samples, including 27 pleomorphic adenomas (PA), 11 Warthin's tumors (WT), six carcinoma ex pleomorphic adenoma (CXPA), six cystic adenocarcinomas (CAC), four mucoepidermoid carcinomas (MEC), three salivary ductal carcinomas (SDC), three adenocarcinomas (ACAR), two oncocitomas (ON), and two epithelium-myoepithelium carcinomas (EMC). Among these samples, 47 were formalin-fixed and paraffin embedded tissues and 17 were fresh tissues. After laser capture microdissection (LCM), the DNA samples were amplified and labeled by PCR-based methods (SCOMP) and nick translation reaction, respectively. Chromosomes were karyotyped based on their inverted DAPI image and the relative hybridization signal intensity was determined along each chromosome. A library with differentially labeled normal samples was built to select the superior and inferior limits for chromosomal gains and losses. Genomic losses were more frequently observed than gains. The comparison among all tumor samples showed common chromosomal imbalances and also exclusive genomic alterations related to the different histological tumor types. Non-random genomic regions involved in pleomorphic adenomas and Warthin's tumors were investigated in databases in order to select candidate genes that could be related to the etiology of these tumors. The NEDD9 (6p24-p25), PPARG (3p25) and c-MYC (8q24.21) genes were selected and the gene transcript levels were evaluated by quantitative real time PCR (qRT-PCR) in PA samples. In accordance to the HR-CGH results, it was observed high transcript levels of NEDD9 in 17 out of 37 PA; low levels of PPARG was detected in 11 out of 36 samples; and high levels... (Complete abstract click electronic access below) / Mestre

The 4.6 Mb circular E. coli chromosome is compacted by segregation into 400-500 supercoiled domains, created by both active and passive mechanisms like transcription and DNA-binding proteins. We find that transposable prophage Mu, transcriptionally silent by definition, is organized into an independent domain as determined by the close proximity of Mu termini L and R separated by a 37 kb Mu genome. Cre-loxP recombination is used in this study in vivo and in vitro. Critical to formation/maintenance of the Mu 'domain' configuration are a strong gyrase site SGS at the center of Mu, the Mu L end, the MuB protein, and the E. coli nucleoid-associated proteins IHF, Fis and HU. The Mu domain was observed at two structurally different chromosomal locations, and was specific to the Mu prophage, i.e. was not observed for the [mathematical symbol] prophage. A model is proposed that by employing its cis-elements to create a domain barrier for segregation and compaction of its genome, the large selfish DNA element Mu profits from the transposition-ready arrangement of its ends, while simultaneously providing a fitness advantage to the host. / text

Haematological cancers like leukemia and lymphoma are characterized by genetic abnormalities, specifically chromosomal translocations. Analyses of the translocation breakpoint regions in patients have shown that some loci in the genome are more susceptible to breakage than others. However, very little is known about the mechanism of generation of many such chromosomal translocations. In the present study, we have attempted to understand the mechanism of fragility of three regions, which are prone to breaks during translocations in follicular lymphoma (FL) and T-cell leukemia. The t(14;18) translocation in FL is one of the most common chromosomal translocations. Most breaks on chromosome 18 are located at the 3’ UTR of the BCL2 gene and are broadly classified into three clusters, namely major breakpoint region (mbr), minor breakpoint cluster region (mcr) and the intermediate cluster region (icr). The RAG complex has been shown to cleave BCL2 mbr by recognizing an altered DNA structure. In the present study, by using a gel based assay, nature of the non-B DNA structure at BCL2 mbr was identified as parallel intramolecular G-quadruplex. Various studies including circular dichroism (CD), mutagenesis, DMS modification assay and 1H NMR showed the presence of three guanine tetrads in the structure. Further, evidence was also found for the formation of such a G-quadruplex structure within mammalian cells. In an effort to characterize the mechanism of fragility of mcr, a unique pattern of RAG cleavage was observed in a sequence dependent manner. Three independent nicks of equal efficiency were generated by RAGs at the cryptic sequence, “CCACCTCT”, at mcr and at a cytosine upstream of it, unlike a single specific nick at the 5’ of heptamer during V(D)J rearrangement. Interestingly, RAG nicking at mcr occured in the presence of both Mg2+ and Mn2+. Using recombination assay, followed by sequencing of the junctions, we find that mcr can recombine with standard RSS in vivo, albeit at a very low frequency. Mutations to this novel motif abolish recombination at the mcr within the cells. In order to determine the prevalence of t(14;18) translocation in the healthy Indian population, nested PCR approach followed by Southern hybridization was used. Results showed 34% prevalence of t(14;18) translocation in the Indian population. Although, no gender based difference was observed, an age dependent increase was found in adults. Further, presence of the t(14;18) transcripts was also detected. The mechanism underlying the fragility of the t(10;14) translocation involving HOX11 gene in T-cell leukemia is not known. Using primer extension assays on a plasmid DNA containing HOX11 breakpoint region, presence of consistent pause sites corresponding to two G-quadruplex forming regions, flanking the patient breakpoints, were detected. These replication blocks were dependent on K+ ions. Native gel shift assays, mutation analysis, S1 nuclease and CD, further revealed formation of intermolecular G-quadruplexes, unlike the BCL2 mbr. Further, sodium bisulfite modification assay indicated the presence of such structures in the genomic DNA within cells. Hence, we propose that two independent G-quadruplex structures formed in the HOX11 gene could interact with each other, thereby resulting in fragility of the intervening sequences, where majority of the patient breakpoints are mapped. Overall, this study has attempted to understand the role of both sequence and structure of DNA, in generating chromosomal fragility during t(14;18) translocation in FL and t(10;14) translocation in T-cell leukemia. These results may facilitate future studies in unraveling the mechanism leading to genomic instability in other lymphoid cancers.

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