Project description:Over 2000 publicly accessible human and mouse ChIP-Seq datasets for about 250 Transcription Factors and chromatin complexes from various databases (ENCODE, GEO) were mapped to custom-made human and mouse genomes containing a reference rDNA sequence of the appropriate species (Genbank U13369.1 for human, BK000964.3 for mouse). The read mapping density across the rDNA sequence was then extracted and normalized to the median in that dataset. Unbiased clustering and analysis, followed by curation, was performed to identify high-confidence patterns of rDNA occupancy for numerous hematopoietic TFs and TF families at canonical TF motif sequences. ************************ Data processing steps: FASTQs were trimmed using Trimmomatic with the following parameters: LEADING:3 TRAILING:3 SLIDINGWINDOW:4:15 MINLEN:30 Reads were mapped to customized genomes (containing additional rDNA sequence) using Bowtie2 using the following parameter: -X 2000 Read density across the rDNA sequence was extracted using igvtools ************************
Project description:Ribosomal RNAs (rRNAs) are essential components of the ribosome and are among the most abundant macromolecules in the cell. To ensure high rRNA level, eukaryotic genomes contain dozens to hundreds of rDNA genes, however, only a fraction of the rRNA genes seems to be active, while others are transcriptionally silent. In Drosophila rDNA units damaged by insertions of retrotransposons are repressed by an unknown mechanism. Here, we established a new model to study regulation of rDNA expression using molecularly marked rDNA transgenes. Using this model, we show that insertion of any heterologous sequence into rDNA leads to transcriptional repression. We found that SUMO (Small Ubiquitin-like Modifier) is required for efficient repression of damaged rDNA units. Surprisingly, SUMO also controls expression of intact rDNA, demonstrating that a single pathway is responsible for both selective repression of damaged units and silencing of surplus rDNA.
Project description:Human preimplantation development is a complex process involving extensive remodeling of gene expression. However, the preimplantation embryo transcriptome has only been annotated using short-read sequencing, which fails to capture full-length mRNAs and associated isoform diversity. We present a novel human embryo transcriptome using integrated long- and short-read RNA sequencing data. Our analysis reveals a total of 110,212 novel isoforms transcribed from known genes containing either a novel combination of known splice sites or at least one novel splice site, and 17,964 isoforms transcribed from completely novel genes located either in antisense direction of known genes or in intergenic space.
Project description:Transcription of the several hundred of mouse and human Ribosomal RNA (rRNA) genes accounts for the majority of RNA synthesis in the cell nucleus and is the determinant of cytoplasmic ribosome abundance, a key factor in regulating gene expression. The rRNA genes, referred to globally as the rDNA, are clustered as direct repeats at the Nucleolar Organiser Regions, NORs, of several chromosomes, and in many cells the active repeats are transcribed at near saturation levels. The rDNA is also a hotspot of recombination and chromosome breakage, and hence understanding its control has broad importance. Despite the need for a high level of rDNA transcription, typically only a fraction of the rDNA is transcriptionally active, and some NORs are permanently silenced by CpG methylation. Various chromatin-remodelling complexes have been implicated in counteracting silencing to maintain rDNA activity. However, the chromatin structure of the active rDNA fraction is still far from clear. Here we have combined a high-resolution ChIP-Seq protocol with conditional inactivation of key basal factors to better understand what determines active rDNA chromatin. The data resolve questions concerning the interdependence of the basal transcription factors, show that preinitiation complex formation is driven by the architectural factor UBF (UBTF) independently of transcription, and exclude a significant role for termination by a torpedomechanism. They further reveal the existence of an asymmetric Boundary Complex formed by CTCF, Cohesin and three phased nucleosomes lying adjacent to the rDNA Enhancer and an arrested RNA Polymerase I complex. We find that this complex is the only site of active histone modification in the whole 45kbp rDNA repeat. Strikingly, the Enhancer Boundary Complex not only delimits each functional rRNA gene, but also is stably maintained after gene inactivation and the re-establishment of surrounding repressive chromatin. Our data define the poised state of rDNA chromatin and place the Enhancer Boundary Complex as the likely entry point for the chromatin remodelling complexes.