RESUMO
We have previously identified Homothorax (Hth) as an important factor for the correct assembly of the pericentromeric heterochromatin during the first fast syncytial divisions of the Drosophila embryo. Here we have extended our studies to later stages of embryonic development. We were able to show that hth mutants exhibit a drastic overall reduction in the tri-methylation of H3 in Lys9, with no reduction of the previous di-methylation. One phenotypic outcome of such a reduction is a genome instability visualized by the many DNA breaks observed in the mutant nuclei. Moreover, loss of Hth leads to the opening of closed heterochromatic regions, including the rDNA genomic region. Our data show that the satellite repeats get transcribed in wild type embryos and that this transcription depends on the presence of Hth, which binds to them as well as to the rDNA region. This work indicates that there is an important role of transcription of non-coding RNAs for constitutive heterochromatin assembly in the Drosophila embryo, and suggests that Hth plays an important role in this process.
Assuntos
Proteínas de Drosophila/metabolismo , Drosophila melanogaster/embriologia , Drosophila melanogaster/metabolismo , Embrião não Mamífero/metabolismo , Desenvolvimento Embrionário , Heterocromatina/metabolismo , Proteínas de Homeodomínio/metabolismo , Fatores de Transcrição/metabolismo , Animais , Sequência de Bases , Sítios de Ligação , Nucléolo Celular/metabolismo , Quebras de DNA , DNA Ribossômico/genética , DNA Satélite/genética , Desoxirribonuclease I/metabolismo , Feminino , Histonas/metabolismo , Lisina/metabolismo , Metilação , Dados de Sequência Molecular , Mutação/genética , Conformação de Ácido Nucleico , Ligação Proteica , RNA Ribossômico/genética , Transcrição GênicaRESUMO
Recent data from a series of laboratories has pinpointed the relevant role of translation control on the regulation of gene expression. In particular, an analysis of T cell activation has led to demonstrate that during this physiological transition about 20% of the regulated mRNAs are controlled at the translation level. Furthermore, modulating the host mRNA translation is one of the mechanisms used by infectious agents to achieve a productive infection. In the present review, we summarize the current knowledge on the translation machinery, the translational control mechanisms during the immune response, as well as the mechanisms used by different pathogens to avoid, inhibit or postpone the host response; and suggest that the analysis on genome-wide screening of the host-pathogen interactions, identifying translationally regulated mRNAs, might unravel new drug targets in infectious diseases.
