RESUMO
Using fluorescence in situ hybridization we show striking differences in nuclear position, chromosome morphology, and interactions with nuclear substructure for human chromosomes 18 and 19. Human chromosome 19 is shown to adopt a more internal position in the nucleus than chromosome 18 and to be more extensively associated with the nuclear matrix. The more peripheral localization of chromosome 18 is established early in the cell cycle and is maintained thereafter. We show that the preferential localization of chromosomes 18 and 19 in the nucleus is reflected in the orientation of translocation chromosomes in the nucleus. Lastly, we show that the inhibition of transcription can have gross, but reversible, effects on chromosome architecture. Our data demonstrate that the distribution of genomic sequences between chromosomes has implications for nuclear structure and we discuss our findings in relation to a model of the human nucleus that is functionally compartmentalized.
Assuntos
Núcleo Celular/genética , Cromossomos Humanos Par 18/ultraestrutura , Cromossomos Humanos Par 19/ultraestrutura , Ciclo Celular/efeitos dos fármacos , Linhagem Celular , Núcleo Celular/efeitos dos fármacos , Núcleo Celular/metabolismo , Células Cultivadas , Centrômero/metabolismo , Centrômero/ultraestrutura , Cromossomos Humanos Par 18/química , Cromossomos Humanos Par 18/genética , Cromossomos Humanos Par 18/metabolismo , Cromossomos Humanos Par 19/química , Cromossomos Humanos Par 19/genética , Cromossomos Humanos Par 19/metabolismo , DNA/metabolismo , Dactinomicina/farmacologia , Diclororribofuranosilbenzimidazol/farmacologia , Fibroblastos/citologia , Fibroblastos/efeitos dos fármacos , Fibroblastos/metabolismo , Inibidores de Histona Desacetilases , Histona Desacetilases/metabolismo , Humanos , Ácidos Hidroxâmicos/farmacologia , Hibridização in Situ Fluorescente , Linfócitos/citologia , Linfócitos/efeitos dos fármacos , Linfócitos/metabolismo , Matriz Nuclear/efeitos dos fármacos , Matriz Nuclear/genética , Matriz Nuclear/metabolismo , RNA Polimerase II/antagonistas & inibidores , RNA Polimerase II/metabolismo , Telômero/metabolismo , Telômero/ultraestrutura , Transcrição Gênica/efeitos dos fármacos , Translocação GenéticaRESUMO
Male meiosis in Mesostoma ehrenbergii ehrenbergii (2x = 10) is characterized by extreme restriction of chiasma formation; 3 pairs of chromosomes form bivalents at metaphase I which are associated by single very distally localized chiasma, while two pairs of chromosomes remain as unpaired univalents. Electron microscopical three-dimensional reconstruction analysis of serial sections has been applied to 20 pachytene spermatocyte nuclei. In each nucleus three short stretches of synaptonemal complex (SC) were found, confined to a localized branched lobe of the nucleus, confirming the findings of an earlier study. The majority of reconstructed nuclei show that each of the three SC segments has a single prominent recombination nodule ("late" RN) associated with it. Late RNs in this system therefore show an excellent correspondence with metaphase I chiasmata, in contrast to a previous report. M.e. ehrenbergii is therefore not an exception to the hypothesis that meiotic exchange requires a functional late RN. A few nuclei had two, one or no RNs; these presumably represent nuclei that are not at the stage of maximum RN presence. Although M. e. ehrenbergii shows pronounced chiasma localization at the light microscope level, at the ultrastructural level RNs are widely distributed along the 5-10 microns of SC formed in each bivalent, indicating that genetic exchange are not restricted to particular localized sites but occur at a large number of DNA sequence.