Evaluation and re-evaluation of genetic radiation hazards in man III. Other relevant data and risk assessment

Some of the advances in mammalian radiation genetics, human genetics and cytogenetics that were made during the last 2–3 years and that have either a direct bearing on, or that may be potentially useful in, the evaluation of genetic radiation hazards in man have been examined. Among these are (1) the new data on the incidence of genetic diseases in man; (2) the latest results of the study of mortality rates among children born to survivors of the atomic bombings of Hiroshima and Nagasaki; (3) new data on the radition-induction of reciprocal translocations in human spermatogonia; (4) new results from radiation studies with mice on skeletal mutations, autosomal recessive lethals, sex-chromosome losses, translocation induction and recovery etc., and (5) a re-analysis of the earlier data on dose-rate effects for the induction of specific locus mutations in mouse spermatogonia. Using the pertinent new information as a basis, quantitative estimates are presented employing both a direct method of expressing risks in terms of effects per unit dose of irradiation and the indirect doubling-dose method of expressing these as increments over the load of genetic disorders occuring spontaneously in man.     

Zinc ion mediated amino acid discrimination by threonyl-tRNA synthetase

Accurate translation of the genetic code depends on the ability of aminoacyl-tRNA synthetases to distinguish between similar amino acids. In order to investigate the basis of amino acid recognition and to understand the role played by the zinc ion present in the active site of threonyl-tRNA synthetase, we have determined the crystal structures of complexes of an active truncated form of the enzyme with a threonyl adenylate analog or threonine. The zinc ion is directly involved in threonine recognition, forming a pentacoordinate intermediate with both the amino group and the side chain hydroxyl. Amino acid activation experiments reveal that the enzyme shows no activation of isosteric valine, and activates serine at a rate 1,000-fold less than that of cognate threonine. This study demonstrates that the zinc ion is neither strictly catalytic nor structural and suggests how the zinc ion ensures that only amino acids that possess a hydroxyl group attached to the beta-position are activated.     

A novel tunnel in mycobacterial type III polyketide synthase reveals the structural basis for generating diverse metabolites

The superfamily of plant and bacterial type III polyketide synthases (PKSs) produces diverse metabolites with distinct biological functions. PKS18, a type III PKS from Mycobacterium tuberculosis, displays an unusual broad specificity for aliphatic long-chain acyl-coenzyme A (acyl-CoA) starter units (C(6)-C(20)) to produce tri- and tetraketide pyrones. The crystal structure of PKS18 reveals a 20 A substrate binding tunnel, hitherto unidentified in this superfamily of enzymes. This remarkable tunnel extends from the active site to the surface of the protein and is primarily generated by subtle changes of backbone dihedral angles in the core of the protein. Mutagenic studies combined with structure determination provide molecular insights into the structural elements that contribute to the chain length specificity of the enzyme. This first bacterial type III PKS structure underlines a fascinating example of the way in which subtle changes in protein architecture can generate metabolite diversity in nature.     

Determination of radiation equivalence of ethyl methanesulphonate (EMS) for induction of gene conversion in diploid yeast.

A unit Rad-Equivalent Chemical (REC) has been suggested for purposes of quantitating the mutagenic hazards of chemicals. The usefulness of this approach is demonstrated by the establishment of a constant relationship between the forward mutation frequency and haploid genome size in various organisms for both radiation and chemical EMS. However, it is necessary to determine the radiation equivalence of chemicals in as many organisms and for as many end-points as possible. For end-points we are limited to forward mutations. Another relevant genetic end-point of interest in this regard is gene conversion which can also monitor any kind of DNA damage in a suitable diploid system. Hence, we have determined the REC value for EMS in diploid yeast with gene conversion as the end-point. This agrees well with the REC values estimated in a number of organisms with forward mutation as the end-point. This finding further underlines the generality of the REC concept.     

Population-Level Scale-Up of Cervical Cancer Prevention Services in a Low-Resource Setting: Development,Implementation, and Evaluation of the Cervical Cancer Prevention Program in Zambia

Background

Very few efforts have been undertaken to scale-up low-cost approaches to cervical cancer prevention in low-resource countries.

Methods

In a public sector cervical cancer prevention program in Zambia, nurses provided visual-inspection with acetic acid (VIA) and cryotherapy in clinics co-housed with HIV/AIDS programs, and referred women with complex lesions for histopathologic evaluation. Low-cost technological adaptations were deployed for improving VIA detection, facilitating expert physician opinion, and ensuring quality assurance. Key process and outcome indicators were derived by analyzing electronic medical records to evaluate program expansion efforts.

Findings

Between 2006-2013, screening services were expanded from 2 to 12 clinics in Lusaka, the most-populous province in Zambia, through which 102,942 women were screened. The majority (71.7%) were in the target age-range of 25–49 years; 28% were HIV-positive. Out of 101,867 with evaluable data, 20,419 (20%) were VIA positive, of whom 11,508 (56.4%) were treated with cryotherapy, and 8,911 (43.6%) were referred for histopathologic evaluation. Most women (87%, 86,301 of 98,961 evaluable) received same-day services (including 5% undergoing same-visit cryotherapy and 82% screening VIA-negative). The proportion of women with cervical intraepithelial neoplasia grade 2 and worse (CIN2+) among those referred for histopathologic evaluation was 44.1% (1,735/3,938 with histopathology results). Detection rates for CIN2+ and invasive cervical cancer were 17 and 7 per 1,000 women screened, respectively. Women with HIV were more likely to screen positive, to be referred for histopathologic evaluation, and to have cervical precancer and cancer than HIV-negative women.

Interpretation

We creatively disrupted the ''no screening'' status quo prevailing in Zambia and addressed the heavy burden of cervical disease among previously unscreened women by establishing and scaling-up public-sector screening and treatment services at a population level. Key determinants for successful expansion included leveraging HIV/AIDS program investments, and context-specific information technology applications for quality assurance and filling human resource gaps.     

Tau Overexpression Impacts a Neuroinflammation Gene Expression Network Perturbed in Alzheimer’s Disease

Filamentous inclusions of the microtubule-associated protein, tau, define a variety of neurodegenerative diseases known as tauopathies, including Alzheimer’s disease (AD). To better understand the role of tau-mediated effects on pathophysiology and global central nervous system function, we extensively characterized gene expression, pathology and behavior of the rTg4510 mouse model, which overexpresses a mutant form of human tau that causes Frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17). We found that the most predominantly altered gene expression pathways in rTg4510 mice were in inflammatory processes. These results closely matched the causal immune function and microglial gene-regulatory network recently identified in AD. We identified additional gene expression changes by laser microdissecting specific regions of the hippocampus, which highlighted alterations in neuronal network activity. Expression of inflammatory genes and markers of neuronal activity changed as a function of age in rTg4510 mice and coincided with behavioral deficits. Inflammatory changes were tau-dependent, as they were reversed by suppression of the tau transgene. Our results suggest that the alterations in microglial phenotypes that appear to contribute to the pathogenesis of Alzheimer’s disease may be driven by tau dysfunction, in addition to the direct effects of beta-amyloid.     

Metagenomic Analysis of the Faecal Microbiome of Rats with 1, 2-Dimethylhydrazine Induced Colon Cancer and Prophylactic Whole-Cell Carotenoid Intervention

Rapidly evolving sequencing technologies have enabled efficient sequencing of complex genomes and metagenomes. Here, we have presented our metagenomic analysis of rat faeces isolated DNA, sequenced using long-read sequencing technology. The microbiome changes in the rat faeces after sixteen weeks of prolonged administration of subcutaneous 1,2 dimethylhydrazine to induce colon carcinogenesis and oral carotenoid-rich whole-cell lyophilised Dunaliella salina supplement. The faecal pellets were aseptically collected, and DNA was isolated and sequenced subsequently. The post-sequencing analysis revealed that the rat gut microbiome is highly complex and diverse. There was a significant difference between the microbiome of rats that received Dunaliella salina supplement in comparison with rats treated with 1,2 dimethylhydrazine and control rats. We observed the dominance of Bacteroidetes over Firmicutes in both cases of administration. The dominance was notably contributed by individuals like B. vulgatus, B. dorei, B. fragilis, P. ruminicola, and P. copri. The presence of protozoans like Trypanosoma, Trichomonas, and Leishmania was also identified among other commensal eukaryotes. Moreover, there was an abundant presence of bacteriophages targeting probiotic organisms like Lactobacillus among the identified DNA viruses.Electronic supplementary materialThe online version of this article (10.1007/s12088-020-00909-z) contains supplementary material, which is available to authorized users.