RESUMEN
The role of Growth Hormone and Dexamethasone in the regulation of rRNA gene activity was evaluated on cultured human fibroblasts by the cyto-chemical method of selective silver staining. By this method the transcriptionally active r-gene clusters can be specifically visualized in individual cells. Statistically significant increases in the rate of rRNA transcriptional activity were demonstrated after hormone administration.
Asunto(s)
ADN Ribosómico/genética , Dexametasona/farmacología , Hormona del Crecimiento/farmacología , Región Organizadora del Nucléolo/fisiología , ARN Ribosómico/genética , Adulto , Células Cultivadas , Embrión de Mamíferos/citología , Femenino , Fibroblastos , Regulación de la Expresión Génica/efectos de los fármacos , Humanos , Región Organizadora del Nucléolo/ultraestructura , Plata , Coloración y EtiquetadoRESUMEN
Hemin-induced K562(S) cells have been studied for the following parameters: cell proliferation, erythroid induction, hemoglobin accumulation, and activation of ribosomal gene clusters 48 hr after hemin induction. Increased transcriptional activity of rRNA genes has been demonstrated by cytochemical methods at both the cell population and single cell level. The following results have been obtained: (a) The vast majority of induced cells shows a highly significant increase in the number of active rRNA gene clusters per cell. At this time, the number of benzidine-positive cells and the quantity of hemoglobin per cell are almost doubled. (b) Specific rRNA gene clusters are activated within single cells. Activation can be visualized at the single gene cluster level. (c) The increase in the average number of active ribosomal gene clusters per cell is not due to clonal selection, but rather to diffuse activation of several gene clusters. (d) The transcriptional activity of rRNA genes has been shown to be regulated at the cellular level by an agent known to specifically induce derepression of genes responsible for erythroid differentiation.
Asunto(s)
Hemo/análogos & derivados , Hemina/farmacología , Leucemia Eritroblástica Aguda/metabolismo , ARN Ribosómico/metabolismo , Diferenciación Celular/efectos de los fármacos , División Celular/efectos de los fármacos , Línea Celular , ADN Ribosómico/análisis , Eritroblastos/efectos de los fármacos , Humanos , CariotipificaciónRESUMEN
The activity of ribosomal gene clusters has been studied by cytological methods in human cultured cells grown in different amounts of serum under controlled experimental conditions. It has been shown that increasing amounts of serum induce an increase in ribosomal RNA synthesis at the single cell level. Furthermore, the concomitant identification of individual rRNA gene clusters by fluorescent techniques allowed us to demonstrate: (1) that individual gene clusters have differential transcriptional activity and differential frequency of activation; (2) that ribosomal gene activity is closely associated with the amount of silver-positive gene product and; (3) that environmental variations modulate rRNA synthesis by repressing or derepressing specific gene clusters.
Asunto(s)
Medios de Cultivo , ADN Ribosómico/biosíntesis , Genes , Transcripción Genética , Sangre , Células Cultivadas , Femenino , Fibroblastos/metabolismo , Humanos , Leucocitos/metabolismo , Región Organizadora del NucléoloRESUMEN
rRNA gene activity was evaluated by cytologic methods in cultured human cells from two different tissues grown under controlled experimental conditions. The modal and average numbers of silver positive nucleolus organizers (NOs) per cell as well as the distribution of cells with different numbers of silver positive NOs and different combinations of D- plus G-group silver stained chromosomes, were evaluated. Statistically significant differences in the average number of silver positive NOs per cell between leukocytes and fibroblasts grown under standard experimental conditions have been demonstrated. The observed differences became sharper in cells cultured under more restrictive conditions. Also, differences in the frequency of silver positivity of specific chromosomal NOs located on individually identified chromosomes were observed in cells from the same tissue. Furthermore, differences in the frequency of activation of rDNA clusters located on the same chromosome were also observed between cells from the two tissues. The possible biologic meanings of these findings are discussed.
Asunto(s)
Genes , Región Organizadora del Nucléolo/ultraestructura , ARN Ribosómico/genética , Células Cultivadas , Femenino , Fibroblastos/ultraestructura , Fluorescencia , Humanos , Cariotipificación , Leucocitos/ultraestructura , Coloración y EtiquetadoRESUMEN
Transcriptional activity of ribosomal RNA (rRNA) genes is detectable around blastula-gastrula transition during the embryonic development of amphibians and other non-mammalian systems. The silver staining reaction, known to selectively stain transcriptionally active nucleolus organizer regions (NORs) both in interphase and metaphase chromosomes allowed us to follow the activation of the NORs during the embryonic development of Xenopus laevis.