Yeast Models of Prion-Like Proteins That Cause Amyotrophic Lateral Sclerosis Reveal Pathogenic Mechanisms

Many proteins involved in the pathogenic mechanisms of amyotrophic lateral sclerosis (ALS) are remarkably similar to proteins that form prions in the yeast Saccharomyces cerevisiae. These ALS-associated proteins are not orthologs of yeast prion proteins, but are similar in having long, intrinsically disordered domains that are rich in hydrophilic amino acids. These so-called prion-like domains are particularly aggregation-prone and are hypothesized to participate in the mislocalization and misfolding processes that occur in the motor neurons of ALS patients. Methods developed for characterizing yeast prions have been adapted to studying ALS-linked proteins containing prion-like domains. These yeast models have yielded major discoveries, including identification of new ALS genetic risk factors, new ALS-causing gene mutations and insights into how disease mutations enhance protein aggregation.

The prionlike domain of FUS is multiphosphorylated following DNA damage without altering nuclear localization

FUS (fused in sarcoma) is an abundant, predominantly nuclear protein involved in RNA processing. Under various conditions, FUS functionally associates with RNA and other macromolecules to form distinct, reversible phase-separated liquid structures. Persistence of the phase-separated state and increased cytoplasmic localization are both hypothesized to predispose FUS to irreversible aggregation, which is a pathological hallmark of subtypes of amyotrophic lateral sclerosis and frontotemporal dementia. We previously showed that phosphorylation of FUS’s prionlike domain suppressed phase separation and toxic aggregation, proportionally to the number of added phosphates. However, phosphorylation of FUS’s prionlike domain was previously reported to promote its cytoplasmic localization, potentially favoring pathological behavior. Here we used mass spectrometry and human cell models to further identify phosphorylation sites within FUS’s prionlike domain, specifically following DNA-damaging stress. In total, 28 putative sites have been identified, about half of which are DNA-dependent protein kinase (DNA-PK) consensus sites. Custom antibodies were developed to confirm the phosphorylation of two of these sites (Ser-26 and Ser-30). Both sites were usually phosphorylated in a subpopulation of cellular FUS following a variety of DNA-damaging stresses but not necessarily equally or simultaneously. Importantly, we found DNA-PK–dependent multiphosphorylation of FUS’s prionlike domain does not cause cytoplasmic localization.

The Role of Post-Translational Modifications on Prion-Like Aggregation and Liquid-Phase Separation of FUS

Subcellular mislocalization and aggregation of the human FUS protein occurs in neurons of patients with subtypes of amyotrophic lateral sclerosis and frontotemporal dementia. FUS is one of several RNA-binding proteins that can functionally self-associate into distinct liquid-phase droplet structures. It is postulated that aberrant interactions within the dense phase-separated state can potentiate FUS's transition into solid prion-like aggregates that cause disease. FUS is post-translationally modified at numerous positions, which affect both its localization and aggregation propensity. These modifications may influence FUS-linked pathology and serve as therapeutic targets.

Sweep optical frequency synthesizer with a distributed-Bragg-reflector laser injection locked by a single component of an optical frequency comb

A sweep optical frequency synthesizer is demonstrated by using a frequency-stabilized optical frequency comb and injection-locked distributed-Bragg-reflector (DBR) laser diode. The injection-locked DBR laser acts as a single-frequency filter and, simultaneously, a high-gain amplifier of the optical frequency comb. The frequency instability of the heterodyne beat signal between two independently injection-locked DBR lasers is measured to be 2.3 x 10(-16) at 1 s averaging time. The output frequency of the sweep optical frequency synthesizer can be precisely tuned over 1 GHz, and a saturated absorption spectrum of the Cs D2 line at 852 nm is recorded by the injected DBR laser.

Pretest assessment as a component of safer sex intervention: a pilot study of brief one-session interventions for women partners of male injection drug users in New York City

This pilot study evaluated whether brief safer sex interventions for women partners of male injection drug users significantly influenced perceptions of partner risk, human immunodeficiency virus (HIV) knowledge, correct condom usage, and self-reported consistent safer sex (abstinence or 100% of vaginal-penile intercourse acts protected by male or female condoms). The study also examined the impact of pretest assessment on those variables since pretest assessment may challenge participants' current knowledge, safer sex practices, and partner communication techniques. The study randomly assigned participants to pretest or no pretest assessment. Each group was also assigned randomly to a presentation modality: (1) safer sex pamphlet review only, (2) pamphlet review with demonstration of several safer sex alternatives, or (3) pamphlet review with skills practice to mastery with one safer sex alternative of the woman's choice. For the last two conditions, a 35-minute interactive session covered prevention efficacy of safer sex methods for HIV, sexually transmitted infections, pregnancy, correct use, eroticization, local cost and availability, and partner objections. At 7 weeks postintervention, a higher proportion of women who took pretest assessment reported consistent safer sex (66.7%) compared to those without pretests (55.6%). Assignment to the interactive interventions (skills or demonstration) had little additional impact over pretest assessment for these women. Among women who did not take pretests, the interactive interventions had strong effects; 76.9% reported consistent safer sex versus 33.3% in the pamphlet review group. There were additional specific effects for pretest assessment on HIV knowledge and partner risk perception and for interactive intervention on correct condom usage. Brief interventions appear to have some positive short-term effects. Pretest assessment may be an important component of brief interventions.

Coherent control of absorption and polarization decay in a GaAs quantum well: time and spectral domain studies

Two phase-locked pulses are used to coherently excite excitonic polarizations. It is shown that the second pulse can either be strongly amplified by taking up energy gained from the destruction of the exciton polarization or can be decreased drastically by giving up all its energy to excitons. Both the temporal and the spectral signatures of the transmitted pulse shapes agree well with model calculations.

Quality of abstracts of original research articles in CMAJ in 1989

PURPOSE

To evaluate the quality of abstracts of original research articles.

DESIGN

Blind, criterion-based survey.

SAMPLE

Systematic sample of 33 abstracts of original research articles published in CMAJ in 1989.

MEASUREMENT

The quality of abstracts was measured against a checklist of evaluation criteria, which were divided into eight categories. A score for each abstract was obtained by dividing the number of criteria present by the number applicable. The overall mean score was also determined.

RESULTS

The overall mean score of abstract quality was 0.63 (standard deviation 0.13) out of 1. Of the abstracts reporting study design 56% did not include specific technical descriptors. About 52% did not explicitly describe the study variables. In describing subject selection 79% failed to use specific technical terms. Of the abstracts reporting results 66% did not provide appropriate supporting data. Of those that gave conclusions 86% did not address study limitations and 93% made no recommendations for future study.

CONCLUSION

Most of the abstracts provided some information pertaining to each evaluation criterion but did not provide detail sufficient to enhance the reader's understanding of the article. On the basis of the study sample the abstracts need improvement in description of research design, reporting of subject selection and results, and statements of limitations and recommendations. The small sample from one journal and the absence of comparison between the contents of the abstracts and the contents of the articles were limitations. Future studies should address these issues and compare the quality of traditional and structured abstracts.