RNA from a simple-tandem repeat is required for sperm maturation and male fertility in Drosophila melanogaster

Tandemly-repeated DNAs, or satellites, are enriched in heterochromatic regions of eukaryotic genomes and contribute to nuclear structure and function. Some satellites are transcribed, but we lack direct evidence that specific satellite RNAs are required for normal organismal functions. Here, we show satellite RNAs derived from AAGAG tandem repeats are transcribed in many cells throughout Drosophila melanogaster development, enriched in neurons and testes, often localized within heterochromatic regions, and important for viability. Strikingly, we find AAGAG transcripts are necessary for male fertility, and that AAGAG RNA depletion results in defective histone-protamine exchange, sperm maturation and chromatin organization. Since these events happen late in spermatogenesis when the transcripts are not detected, we speculate that AAGAG RNA in primary spermatocytes ‘primes’ post-meiosis steps for sperm maturation. In addition to demonstrating essential functions for AAGAG RNAs, comparisons between closely related Drosophila species suggest that satellites and their transcription evolve quickly to generate new functions.

Telomeric small RNAs in the genus Caenorhabditis

Telomeric DNA is composed of simple tandem repeat sequences and has a G-rich strand that runs 5’ to 3’ towards the chromosome terminus. Small RNAs with homology to telomeres have been observed in several organisms and could originate from telomeres or from interstitial telomere sequences (ITSs), which are composites of degenerate and perfect telomere repeat sequences found on chromosome arms. We identified C. elegans small RNAs composed of the Caenorhabditis telomere sequence (TTAGGC)n with up to three mismatches, which might interact with telomeres. We rigorously defined ITSs for genomes of C. elegans and for two closely related nematodes, C. briggsae and C. remanei. We found that most telomeric small RNAs with mismatches originated from ITSs, which were depleted from mRNAs and but were enriched in introns whose genes often displayed hallmarks of genomic silencing. C. elegans small RNAs composed of perfect telomere repeats were very rare but were increased by several orders of magnitude in C. briggsae and C. remanei. Major small RNA species in C. elegans begin with a 5’ guanine nucleotide, which was strongly depleted from perfect telomeric small RNAs of all three Caenorhabditis species. Perfect telomeric small RNAs corresponding to the G-rich strand of the telomere commonly began with 5’ UAGGCU and 5’UUAGGC, whereas C-rich strand RNAs commonly begin with 5’CUAAGC. In contrast, telomeric small RNAs with mismatches had a mixture of all four 5’ nucleotides. Together, our results imply that perfect telomeric small RNAs have a mechanism of biogenesis that is distinct from known classes of small RNAs and that a dramatic change in their regulation occurred during recent Caenorhabditis evolution.

PCR-based tissue identification: the UCLH experience

The need to accurately identify tissue of an individual can arise in a variety of settings including mislabelled slides or sample carryover. Reported rates of carryover range from 0.6% to 2.9% of slides depending on the methods of evaluation. Carryover becomes particularity clinically important when malignant tissue is found in an otherwise benign sample. The suspicion of malignancy causes immense psychological stress to the patient and results in additional management costs due to the additional investigations required to rule out malignancy. Proving a negative can be difficult and many cases result in lifelong follow-up for the patient. Molecular techniques such as PCR amplification of simple tandem repeat (STR) sequences can be used to identify tissue and hence its provenance. At University College London Hospital, STR PCR analysis has been used since 2003. Here the authors report their experience with regard to the clinical scenarios, the technique used and the outcomes.

Candidate Gene Discovery Procedure after Follow-Up Confirmatory Analyses of Candidate Regions of Interests for Alzheimer’s Disease in the NIMH Sibling Dataset

The objective of this research was to develop a procedure to identify candidate genes under linkage peaks confirmed in a follow-up of candidate regions of interests (CRIs) identified in our original genome scan in the NIMH Alzheimer’s diseases (AD) Initiative families (Blacker et al. [1]). There were six CRIs identified that met the threshold of multipoint lod score (MLS) of ≥ 2.0 from the original scan. The most significant peak (MLS = 7.7) was at 19q13, which was attributed toAPOE. The remaining CRIs with ‘suggestive’ evidence for linkage were identified at 9q22, 6q27, 14q22, 11q25, and 3p26. We have followed up and narrowed the 9q22 CRI signal using simple tandem repeat (STR) markers (Perry et al. [2]). In this confirmatory project, we have followed up the 6q27, 14q22, 11q25, and 3p26 CRIs with a total of 24 additional flanking STRs, reducing the mean interval marker distance (MID) in each CRI, and substantially increase in the information content (IC). The linkage signals at 6q27, 14q22 and 11q25 remain ‘suggestive’, indicating that these CRIs are promising and worthy of detailed fine mapping and assessment of candidate genes associated with AD.We have developed a bioinformatics approach for identifying candidate genes in these confirmed regions based on the Gene Ontology terms that are annotated and enriched among the systematic meta-analyzed genes, confirmed by at least three case-control samples, and cataloged in the “AlzGene database” as potential Alzheimer disease susceptibility genes (http://www.alzgene.org).