DNA fragmentation by gamma radiation and electron beams using atomic force microscopy.

Double-stranded pBS plasmid DNA was irradiated with gamma rays at doses ranging from 1 to 12 kGy and electron beams from 1 to 10 kGy. Fragment-size distributions were determined by direct visualization, using atomic force microscopy with nanometer-resolution operating in non-tapping mode, combined with an improved methodology. The fragment distributions from irradiation with gamma rays revealed discrete-like patterns at all doses, suggesting that these patterns are modulated by the base pair composition of the plasmid. Irradiation with electron beams, at very high dose rates, generated continuous distributions of highly shattered DNA fragments, similar to results at much lower dose rates found in the literature. Altogether, these results indicate that AFM could supplement traditional methods for high-resolution measurements of radiation damage to DNA, while providing new and relevant information.

Static electric fields interfere in the viability of cells exposed to ionising radiation.

PURPOSE: The interference of electric fields (EF) with biological processes is an issue of considerable interest. No studies have as yet been reported on the combined effect of EF plus ionising radiation. Here we report studies on this combined effect using the prokaryote Microcystis panniformis, the eukaryote Candida albicans and human cells. MATERIALS AND METHODS: Cultures of Microcystis panniformis (Cyanobacteria) in glass tubes were irradiated with doses in the interval 0.5-5 kGy, using a (60)Co gamma source facility. Samples irradiated with 3 kGy were exposed for 2 h to a 20 V . cm(-1) static electric field and viable cells were enumerated. Cultures of Candida albicans were incubated at 36 degrees C for 20 h, gamma-irradiated with doses from 1-4 kGy, and submitted to an electric field of 180 V . cm(-1). Samples were examined under a fluorescence microscope and the number of unviable (red) and viable (apple green fluorescence) cells was determined. For crossing-check purposes, MRC5 strain of lung cells were irradiated with 2 Gy, exposed to an electric field of 1250 V/cm, incubated overnight with the anti-body anti-phospho-histone H2AX and examined under a fluorescence microscope to quantify nuclei with gamma-H2AX foci. RESULTS: In cells exposed to EF, death increased substantially compared to irradiation alone. In C. albicans we observed suppression of the DNA repair shoulder. The effect of EF in growth of M. panniformis was substantial; the number of surviving cells on day-2 after irradiation was 12 times greater than when an EF was applied. By the action of a static electric field on the irradiated MRC5 cells the number of nuclei with gamma-H2AX foci increased 40%, approximately. CONCLUSIONS: Application of an EF following irradiation greatly increases cell death. The observation that the DNA repair shoulder in the survival curve of C. albicans is suppressed when cells are exposed to irradiation + EF suggests that EF likely inactivate cellular recovering processes. The result for the number of nuclei with gamma-H2AX foci in MRC5 cells indicates that an EF interferes mostly in the DNA repair mechanisms. A molecular ad-hoc model is proposed.

Genética molecular e odontologia forense / Molecular genetics and forensic odontology

A identificaçäo postmortem precisa de indivíduos vítimas de traumatismos representa um desafio para os especialistas em Odontologia Forense e Medicina Legal. Apesar das técnicas convencionais apresentarem resultados confiáveis, a metodologia genético-molecular firma-se como o alicerce futuro para este tipo de procedimento. Destas, a identificaçäo genética baseada no seqüenciamento e isolamento do DNA mitocondrial dentário denota um extraordinário e promissor avanço, seja pela resistência e durabilidade do tecido envolvido (no caso, o dente), seja pelo tipo de DNA utilizado (pois o DNA mitocondrial já foi completamente mapeado e clonado). Apresentamos, nesta revisäo, alguns aspectos das etapas de extraçäo, ampliaçäo e as formas de seqüenciamento disponíveis para o estudo do DNA, nuclear e mitocontrial, humano

Aspectos genéticos do desenvolvimento cranio facial / Craniofacial development genetic aspects

A Genética do Desenvolvimento é a área da Biologia voltada para o estudo e entendimento da regulaçäo dos genes que permitem a um ovócito fertilizado desenvolver-se até um organismo maduro. Este estudo é direcionado em campos de desenvolvimento e, um deles é o segmento craniofacial. Acredita-se que os genes HOXB1, A2, B2, A3, B3, D3, B4 e C4 sejam transcritos nas regiöes das bolsas faríngeas, e assim, envolvidos com a gênese, por exemplo, da síndrome de DiGeorge (com fendas lábio-palatinas, filtro curto e outros comemorativos). Além dos genes homeobox, genes estruturais simples estäo envolvidos na etiologia de malformaçöes craniofaciais como a Displasia Crânio-Fronto-Nasal cujo gene foi recentemente mapeado em Xp22. O entendimento dos mecanismos anormais destes genes pode propiciar novas perspectivas diagnósticas e terapêuticas no campo da dismorfologia craniofacial