RESUMO
The article reviews the existing methods of multicolor FISH on nuclear targets, first of all, interphase chromosomes. FISH proper and image acquisition are considered as two related components of a single process. We discuss (1) M-FISH (combinatorial labeling + deconvolution + wide-field microscopy); (2) multicolor labeling + SIM (structured illumination microscopy); (3) the standard approach to multicolor FISH + CLSM (confocal laser scanning microscopy; one fluorochrome - one color channel); (4) combinatorial labeling + CLSM; (5) non-combinatorial labeling + CLSM + linear unmixing. Two related issues, deconvolution of images acquired with CLSM and correction of data for chromatic Z-shift, are also discussed. All methods are illustrated with practical examples. Finally, several rules of thumb helping to choose an optimal labeling + microscopy combination for the planned experiment are suggested.
Assuntos
Núcleo Celular/ultraestrutura , Hibridização in Situ Fluorescente/métodos , Interfase/genética , Núcleo Celular/genética , Coloração Cromossômica , Cor , Humanos , Microscopia de FluorescênciaRESUMO
The C-terminal domain (CTD) of mammalian RNA polymerase II consists of 52 repeats of the consensus hepta-peptide YSPTSPS, and links transcription to the processing of pre-mRNA. Although Pol II with a CTD shortened to five repeats (Pol II Delta5) is transcriptionally inactive on chromatin templates, it is not clear whether CTD is required for promoter recognition in vivo. Here, we demonstrate that in the context of chromatin, Pol II Delta5 can bind to the c-myc promoter with the same efficiency as wild type Pol II. However, Pol II Delta5 does not form a stable initiation complex, and does not transcribe promoter proximal sequences. Fluorescence recovery after photobleaching (FRAP) experiments with cells expressing enhanced green fluorescent protein (EGFP)-tagged Delta5 or wildtype Pol II revealed a single, highly mobile Pol II Delta5 fraction whereas wildtype Pol II yielded less mobile fractions. These data suggest that CTD is not required for promoter recognition, but rather for subsequent formation of a stable initiation complex and isomerization to an elongation competent complex.
Assuntos
Regiões Promotoras Genéticas , RNA Polimerase II/química , Transcrição Gênica , Sítios de Ligação , Linhagem Celular Tumoral , Núcleo Celular/enzimologia , Sequência Consenso , Recuperação de Fluorescência Após Fotodegradação , Genes myc , Proteínas de Fluorescência Verde/análise , Humanos , Estrutura Terciária de Proteína , RNA Polimerase II/genética , RNA Polimerase II/metabolismo , Sequências Repetitivas de Aminoácidos , Deleção de SequênciaRESUMO
Histone modifications represent an important epigenetic mechanism for the organization of higher order chromatin structure and gene regulation. Methylation of position-specific lysine residues in the histone H3 and H4 amino termini has linked with the formation of constitutive and facultative heterochromatin as well as with specifically repressed single gene loci. Using an antibody, directed against dimethylated lysine 9 of histone H3 and several other lysine methylation sites, we visualized the nuclear distribution pattern of chromatin flagged by these methylated lysines in 3D preserved nuclei of normal and malignant cell types. Optical confocal serial sections were used for a quantitative evaluation. We demonstrate distinct differences of these histone methylation patterns among nuclei of different cell types after exit of the cell cycle. Changes in the pattern formation were also observed during the cell cycle. Our data suggest an important role of methylated histones in the reestablishment of higher order chromatin arrangements during telophase/early G1. Cell type specific histone methylation patterns are possibly casually involved in the formation of cell type specific heterochromatin compartments, composed of (peri)centromeric regions and chromosomal subregions from neighboring chromosomes territories, which contain silent genes.