Group I introns are a distinct class of RNA self-splicing introns with an ancient origin. All known group I introns present in eukaryote nuclei interrupt functional ribosomal RNA genes located in ribosomal DNA loci. The discovery of the Tetrahymena intron more than 30 years ago has been essential to our understanding of group I intron catalysis, higher-order RNA structure, and RNA folding, but other intron models have provided information about the biological role. Nuclear group I introns appear widespread among eukaryotic microorganisms, and the plasmodial slime molds (myxomycetes) contain an abundance of self-splicing introns. Here, we summarize the main conclusions from previous work on the Tetrahymena intron on RNA self-splicing catalysis as well as more recent work on myxomycete intron biology. Group I introns in myxomycetes that represent different evolutionary stages, biological roles, and functional settings are discussed.

The present review focuses on pathogenic molecular and transcriptional events in patients with lupus nephritis. These factors are renal DNaseI, exposed chromatin fragments and the corresponding chromatin-reactive autoantibodies. Lupus nephritis is the most serious complication in human systemic lupus erythematosus, and is characterised by deposition of chromatin fragment-IgG complexes in the mesangial matrix and glomerular basement membranes. The latter deposition defines end-stage disease. This event is stringently linked to a renal-restricted shutdown of expression of the DNaseI gene, as determined by loss of DNaseI mRNA level and DNaseI enzyme activity. The major aim of the present review is to generate new therapeutic strategies based on new insight into the disease pathogenesis.

Low-level mitochondrial heteroplasmy is a common phenomenon in both normal and cancer cells. Here, we investigate the link between low-level heteroplasmy and mitogenome mutations in a human breast cancer matched cell line by high-throughput sequencing. We identified 23 heteroplasmic sites, of which 15 were common between normal cells (Hs578Bst) and cancer cells (Hs578T). Most sites were clustered within the highly conserved Complex IV and ribosomal RNA genes. Two heteroplasmic variants in normal cells were found as fixed mutations in cancer cells. This indicates a positive selection of these variants in cancer cells. RNA-Seq analysis identified upregulated L-strand specific transcripts in cancer cells, which include three mitochondrial long non-coding RNA molecules. We hypothesize that this is due to two cancer cell-specific mutations in the control region.

Background: The ribosomal DNA (rDNA) of the myxomycete Didymium iridis is located on a linear, multi-copy, non-Mendelian chromosome. Efforts to determine the complete sequence by short-read sequencing technologies have been prevented by the presence of highly repetitive regions. Here we use high coverage (~10,000 x) long-read Oxford Nanopore Technology to determine the rDNA chromosome sequence in haploid amoebae from telomere-to-telomere. Results: The 20 kb rDNA chromosome, which is present at ~ 132 copies per haploid genome, is capped by regular TTAGGG telomeric repeats at both ends and carries an 11.3 kb pre-rRNA transcription unit coding for the small and large subunit rRNAs. The rRNA genes are further interrupted by autocatalytic group I introns, one of which encodes a homing endonuclease and two catalytic RNA domains with different functions in RNA processing. RNA mapping analyses from amoeba, microcyst, flagellate, and plasmodium stages, based on Illumina short-read sequencing, support the presence of a mature intron homing endonuclease mRNA both in haploid and diploid life stages in D. iridis . The non-transcribed sequence region upstream of the transcription unit contains several direct repeat arrays, including a highly complex upstream promoter region likely to be involved in pre-rRNA transcription regulation. Adjacent to the upstream telomere, a 4.2 kb palindromic region with potential for cruciform structure formation is found. Here, two putative replication origin candidates are located. Conclusions: High coverage Oxford Nanopore Technology sequencing results in excellent resolution of complex sequence repeat feature in the D. iridis rDNA chromosome. The rRNA genes are interrupted by complex group I introns and RNA sequencing supports intron autocatalytic processing in haploid and diploid life stages. This study provides new insights into structural arrangements of nuclear rDNA in eukaryotic microorganisms.