A novel motif of Rad51 serves as an interaction hub for recombination auxiliary factors

Homologous recombination (HR) is essential for maintaining genome stability. Although Rad51 is the key protein that drives HR, multiple auxiliary factors interact with Rad51 to potentiate its activity. Here, we present an interdisciplinary characterization of the interactions between Rad51 and these factors. Through structural analysis, we identified an evolutionarily conserved acidic patch of Rad51. The neutralization of this patch completely abolished recombinational DNA repair due to defects in the recruitment of Rad51 to DNA damage sites. This acidic patch was found to be important for the interaction with Rad55-Rad57 and essential for the interaction with Rad52. Furthermore, biochemical reconstitutions demonstrated that neutralization of this acidic patch also impaired the interaction with Rad54, indicating that a single motif is important for the interaction with multiple auxiliary factors. We propose that this patch is a fundamental motif that facilitates interactions with auxiliary factors and is therefore essential for recombinational DNA repair.

Cooperative interactions facilitate stimulation of Rad51 by the Swi5-Sfr1 auxiliary factor complex

Although Rad51 is the key protein in homologous recombination (HR), a major DNA double-strand break repair pathway, several auxiliary factors interact with Rad51 to promote productive HR. We present an interdisciplinary characterization of the interaction between Rad51 and Swi5-Sfr1, a conserved auxiliary factor. Two distinct sites within the intrinsically disordered N-terminus of Sfr1 (Sfr1N) were found to cooperatively bind Rad51. Deletion of this domain impaired Rad51 stimulation in vitro and rendered cells sensitive to DNA damage. By contrast, amino acid-substitution mutants, which had comparable biochemical defects, could promote DNA repair, suggesting that Sfr1N has another role in addition to Rad51 binding. Unexpectedly, the DNA repair observed in these mutants was dependent on Rad55-Rad57, another auxiliary factor complex hitherto thought to function independently of Swi5-Sfr1. When combined with the finding that they form a higher-order complex, our results imply that Swi5-Sfr1 and Rad55-Rad57 can collaboratively stimulate Rad51 in Schizosaccharomyces pombe.

Do Age at Diagnosis, Tumour Thickness and Tumour Site Explain Sex Differences in Melanoma Survival? A Sequential Causal Mediation Analysis Using Cancer Registry Data

Background: Previous research has shown that women diagnosed with melanoma have better survival than their male counterparts, but little is known about the underlying mechanisms by which sex affects melanoma survival. Aim: The aim of this study was to quantify the contribution of age at diagnosis, tumor thickness and tumor site to sex differences in 1-year and 5-year melanoma-specific survival. Methods: We conducted a population-based study using cancer registry data including 6,009 men and 5,232 women aged 15-70 years with first primary melanoma diagnosed between 2007 and 2015 in Victoria, Australia. We excluded cases notified via death certificate only. Deaths to the end of 2015 were identified through linkage to the Victorian and national death registries. We decomposed the total effect of sex on melanoma-specific survival into three possible pathways, examining the mediating role of age at diagnosis, tumor thickness and tumor site. The natural indirect effects through the mediators were assessed using weighted, sequential causal mediation analysis. Results: Compared with women, there were 60 (95% confidence interval (CI) 34 to 91) and 201 (95% CI 135 to 267) additional deaths per 10,000 in men within 1 year and 5 years following diagnosis, respectively. Within 1 year following diagnosis, the indirect effect through age at diagnosis was estimated to be 4 (95% CI -2 to 9) additional deaths per 10,000 in men compared with women, explaining 7% of the total effect of sex, while a considerable proportion of the total effect (79%) explained by melanoma thickness [47 (95% CI 32 to 66) additional deaths per 10,000 in men], excluding the potential influence of age at diagnosis on thickness. Similarly, within 5 years after diagnosis, about 13% of the total effect was estimated to be explained by age at diagnosis [26 (95% CI 15 to 38) additional deaths per 10,000 in men] and 86% by tumor thickness [174 (95% CI 142 to 207) additional death per 10,000 in men]. There was no indirect effect through tumor site within 1 year and 5 years postdiagnosis. Conclusion: The lower survival from melanoma of men relative to women appears to be explained primarily by tumor thickness rather than age at diagnosis. Our findings highlight the need for earlier detection of melanoma in men.

Fundamental cell cycle kinases collaborate to ensure timely destruction of the synaptonemal complex during meiosis

The synaptonemal complex (SC) is a proteinaceous macromolecular assembly that forms during meiotic prophase I and mediates adhesion of paired homologous chromosomes along their entire lengths. Although prompt disassembly of the SC during exit from prophase I is a landmark event of meiosis, the underlying mechanism regulating SC destruction has remained elusive. Here, we show that DDK (Dbf4-dependent Cdc7 kinase) is central to SC destruction. Upon exit from prophase I, Dbf4, the regulatory subunit of DDK, directly associates with and is phosphorylated by the Polo-like kinase Cdc5. In parallel, upregulated CDK1 activity also targets Dbf4. An enhanced Dbf4-Cdc5 interaction pronounced phosphorylation of Dbf4 and accelerated SC destruction, while reduced/abolished Dbf4 phosphorylation hampered destruction of SC proteins. SC destruction relieved meiotic inhibition of the ubiquitous recombinase Rad51, suggesting that the mitotic recombination machinery is reactivated following prophase I exit to repair any persisting meiotic DNA double-strand breaks. Taken together, we propose that the concerted action of DDK, Polo-like kinase, and CDK1 promotes efficient SC destruction at the end of prophase I to ensure faithful inheritance of the genome.

The synaptonemal complex is assembled by a polySUMOylation-driven feedback mechanism in yeast

Synaptonemal complex (SC) assembly requires polySUMOylation of Ecm11, which promotes polymerization of Zip1, the transverse filament, whereas the N terminus of Zip1 activates Ecm11 polySUMOylation, suggesting that this positive feedback loop underpins SC assembly.

During meiotic prophase I, proteinaceous structures called synaptonemal complexes (SCs) connect homologous chromosomes along their lengths via polymeric arrays of transverse filaments (TFs). Thus, control of TF polymerization is central to SC formation. Using budding yeast, we show that efficiency of TF polymerization closely correlates with the extent of SUMO conjugation to Ecm11, a component of SCs. HyperSUMOylation of Ecm11 leads to highly aggregative TFs, causing frequent assembly of extrachromosomal structures. In contrast, hypoSUMOylation leads to discontinuous, fragmented SCs, indicative of defective TF polymerization. We further show that the N terminus of the yeast TF, Zip1, serves as an activator for Ecm11 SUMOylation. Coexpression of the Zip1 N terminus and Gmc2, a binding partner of Ecm11, is sufficient to induce robust polySUMOylation of Ecm11 in nonmeiotic cells. Because TF assembly is mediated through N-terminal head-to-head associations, our results suggest that mutual activation between TF assembly and Ecm11 polySUMOylation acts as a positive feedback loop that underpins SC assembly.

Conserved metallomics in two insect families evolving separately for a hundred million years

Μetal cofactors are required for enzymatic catalysis and structural stability of many proteins. Physiological metal requirements underpin the evolution of cellular and systemic regulatory mechanisms for metal uptake, storage and excretion. Considering the role of metal biology in animal evolution, this paper asks whether metal content is conserved between different fruit flies. A similar metal homeostasis was previously observed in Drosophilidae flies cultivated on the same larval medium. Each species accumulated in the order of 200 µg iron and zinc and approximately ten-fold less manganese and copper per gram dry weight of the adult insect. In this paper, data on the metal content in fourteen species of Tephritidae, which are major agricultural pests worldwide, are presented. These fruit flies can be polyphagous (e.g., Ceratitis capitata) or strictly monophagous (e.g., Bactrocera oleae) or oligophagous (e.g., Anastrepha grandis) and were maintained in the laboratory on five distinct diets based on olive oil, carrot, wheat bran, zucchini and molasses, respectively. The data indicate that overall metal content and distribution between the Tephritidae and Drosophilidae species was similar. Reduced metal concentration was observed in B. oleae. Feeding the polyphagous C. capitata with the diet of B. oleae resulted in a significant quantitative reduction of all metals. Thus, dietary components affect metal content in some Tephritidae. Nevertheless, although the evidence suggests some fruit fly species evolved preferences in the use or storage of particular metals, no metal concentration varied in order of magnitude between these two families of Diptera that evolved independently for over 100 million years.

A recessive X-linked mutation causes a threefold reduction of total body zinc accumulation in Drosophila melanogaster laboratory strains

A newly identified human locus on chromosome 15 was recently associated with zinc accumulation. Based on a prior report of a threefold difference in zinc accumulation between fumble¹ heterozygous mutants and control fly strains, it was suggested that phosphopantothenoylcysteine decarboxylase might affect zinc status through its effects on vitamin B5 (pantothenate) metabolism. We report here that outcrossed fumble¹ heterozygous mutant flies with low zinc content have been recovered, suggesting that pantothenate metabolism did not alter zinc homeostasis in fumble¹ heterozygous flies. We show instead that the Drosophila condition of low body zinc accumulation is an X-chromosome-linked recessive trait.

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Flies with a threefold reduction in zinc accumulation remain viable and fertile.

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There is no causal association between zinc accumulation and fly pantothenate kinase mutants.

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A widespread X-linked mutation causes a threefold reduction in zinc accumulation in Drosophila.

Injuries due to Landmine Blast Referred to Shahid Motahhary Hospital, Iran

BACKGROUND

The health system faced a new problem of an increasing number of civilian victims of landmine explosions at the end of Iran-Iraq war.

METHODS

In a descriptive survey from 1998 to 2004, data was collected retrospectively from medical records of Shahid Motahhary Hospital, Urmia University of Medical Sciences, Iran.

RESULT

The study covered 156 victims. 80% of the casualties were civilians of which 95% were male. Injuries led to amputation in 73.3% of the victims. The mortality rate was 3.8%. Blood transfusions was given to 93 (62%) victims. There were 52.6% pattern I, 14.6% pattern II and 32.6% pattern III injuries according to International Committee of the Red Cross (ICRC) classification.

CONCLUSION

Mine awareness programs should be conducted amongst civilians who live in high-risk areas. Improved health infrastructure with trained personals for emergency care and early transfer of the casualties would reduce morbidity and mortality. Studies are required to understand the social and public health consequences of this problem.