Strand specific transcription of satellite DNA I in rat ascites hepatoma cells

Human pericentromeric tandemly repeated DNA is transcribed at the end of oocyte maturation and is associated with membraneless mitochondria-associated structures

Most of the human genome is non-coding. However, some of the non-coding part is transcriptionally active. In humans, the tandemly repeated (TR) pericentromeric non-coding DNA-human satellites 2 and 3 (HS2, HS3)-are transcribed in somatic cells. These transcripts are also found in pre- and post-implantation embryos. The aim of this study was to analyze HS2/HS3 transcription and cellular localization of transcripts in human maturating oocytes. The maternal HS2/HS3 TR transcripts transcribed from both strands were accumulated in the ooplasm in GV-MI oocytes as shown by DNA-RNA FISH (fluorescence in-situ hybridization). The transcripts' content was higher in GV oocytes than in somatic cumulus cells according to real-time PCR. Using bioinformatics analysis, we demonstrated the presence of polyadenylated HS2 and HS3 RNAs in datasets of GV and MII oocyte transcriptomes. The transcripts shared a high degree of homology with HS2, HS3 transcripts previously observed in cancer cells. The HS2/HS3 transcripts were revealed by a combination of FISH and immunocytochemical staining within membraneless RNP structures that contained DEAD-box helicases DDX5 and DDX4. The RNP structures were closely associated with mitochondria, and are therefore similar to membraneless bodies described previously only in oogonia. These membraneless structures may be a site for spatial sequestration of RNAs and proteins in both maturating oocytes and cancer cells.

The role of ncRNA in centromeres: a lesson from marsupials

Though centromeres have been thought to be comprised of repetitive, transcriptionally inactive DNA, new evidence suggests that eukaryotic centromeres produce a variety of transcripts and that RNA is essential for centromere competence. It has been proposed that centromere satellite transcripts play an essential role in centromere function through demarcation of the kinetochore-binding domain. However, the regional limits and regulation of transcription within the mammalian centromere are unknown. Analysis of transcriptional domains within the centromere in mammalian models is impeded by the unbridgeable expanse of satellite monomers throughout the pericentromere. The comparatively small size of the wallaby centromere and the evolutionary role of the centromere in marsupial speciation events position the wallaby centromere as a tractable and valuable mammalian centromere model. We highlight the current understanding of the wallaby centromere and the role of transcription in centromere function.

Structural and functional characterization of noncoding repetitive RNAs transcribed in stressed human cells

Thermal and chemical stresses induce the formation in human cells of novel and transient nuclear structures called nuclear stress bodies (nSBs). These contain heat shock factor 1 (HSF-1) and a specific subset of pre-mRNA processing factors. Nuclear stress bodies are assembled on specific pericentromeric heterochromatic domains containing satellite III (SatIII) DNA. In response to stress, these domains change their epigenetic status from heterochromatin to euchromatin and are transcribed in poly-adenylated RNAs that remain associated with nSBs. In this article, we describe the cloning, sequencing, and functional characterization of these transcripts. They are composed of SatIII repeats and originate from the transcription of multiple sites within the SatIII arrays. Interestingly, the level of SatIII RNAs can be down-regulated both by antisense oligonucleotides and small interfering RNAs (siRNA). Knockdown of SatIII RNA by siRNAs requires the activity of Argonaute 2, a component of the RNA-induced silencing complex. Down-regulation of satellite III RNAs significantly affects the recruitment of RNA processing factors to nSBs without altering the association of HSF-1 with these structures nor the presence of acetylated histones within nSBs. Thus, satellite III RNAs have a major role in the formation of nSBs.

A systematic survey of repetitive sequences abundantly expressed in rat tumors

A cDNA library made from poly(A)+ RNA of a rat ascites hepatoma cell line, AH60C, was screened with respect to transcribed repetitive sequences by probing with AH60C genomic DNA. Thirty clones, comprising 1.2% of the library, were found to contain repetitive elements. The sequences of 12 clones among them were abundantly expressed in poly(A)+ RNA of AH60C, yet sparse in that of rat normal liver. This differential expression was also noted in case of other tumors and normal tissues tested. These 12 clones could be divided into two classes, depending on whether their sequences were expressed in cytoplasmic poly(A)+ RNA (class I) or not (class II). Rat Alu-like type II (B2) repeats and an unknown repetitive sequence were found in the clones of class I. Adjacent to each of them, we detected two non-repeated sequences, the expressions of which were also activated. The presence of another unknown repetitive sequence was observed in the clones of class II. It is noted that more than one-third of the transcribed repetitive sequences were involved in the predominant expression in tumor cells, whereas the majority of overall transcripts have been found to be common to both transformed cells and their normal counterparts.

A new family of LTR-like sequences abundantly expressed in rat tumors

We report the identification of two genome DNA fragments containing middle repetitive sequences abundantly expressed in various rat tumors but rarely in normal tissues. These fragments included homologous regions which belonged to a new family of long terminal repeat (LTR) like sequences, designated RAL elements; one displayed the solitary type and the other a provirus structure. The element was transcribed in a strand specific fashion and started from the presumptive cap site within the RAL element. The presumptive polyA addition site within the element was also utilized as evidence of the analysis of a cDNA clone containing the RAL element. This evidence suggested that transcriptional control signals within the element were functioning. Run on assay revealed that expression of the element was regulated at the transcriptional level.