Crystalline Aggregates Research Articles

UV-light-driven cadmium sulphide (CdS) nanocatalysts: synthesis, characterization, therapeutic and environmental applications; kinetics and thermodynamic study of photocatalytic degradation of Eosin B and Methyl Green dyes.

Cadmium sulphide (CdS) nanoparticles (NPs) were synthesized through hydrothermal route and characterized by UV-Vis spectroscopy, X-ray diffraction (XRD), Energy dispersive X-ray analysis, Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy and Thermo gravimetric analysis (TGA).The band gap of CdS nanoparticles was found to be 2.38 eV. CdS NPs are crystalline aggregates with hexagonal structure as shown by SEM and XRD analysis. TGA study revealed that the synthesized nanomaterials were very stable to temperature and only 6.54% total loss occurred during heating range (25 °C-600 °C).The CdS NPs were used for the first time against the degradation of Eosin B (EB) and Methyl green (MG) dyes in aqueous solution.The degradation of EB and MG over CdS nanocatalysts followed second order kinetics. The predicted activation energies for both the dyes' reactions were 61.1 kJ/mol and 32.11 kJ/mol, respectively. About 95% and 90% dye degradation was observed at the time interval of 160 minutes for EB and MG, respectively. High percent degradation of EB was observed at high pH (pH 0) while at low pH (pH 4) high percent degradation was found for MG dye. Maximum dye degradation was found at the optimal dose (0.03 g/L) of the catalyst and at low dye concentration. The rate of EB and MG dye degradation was found to increase with increase in temperature up to 45 °C. The recyclability study showed that CdS nanoparticles could be reused for the degradation of the given dyes. Good antibacterial activity against Staphylococcus aureus was shown by CdS NPs. From the biocompatibility it was confirmed that CdS NPS are bioincompatible compatible.

Dve nové lokality pyromorfitu v Slovenskej republike: Chvojnica a Hnilčík

Two new localities of pyromophite were recently discovered at the Chvojnica base metals occurrence in the Strážovské vrchy Mts. (Tatric Unit), and at the supergene zone of the Piata siderite-type hydrothermal vein near Hnilčík (Spišsko-gemerské rudohorie Mts., Gemeric Unit), Slovak Republic. At the Chvojnica occurrence pyromorphite occurs as bright green crystalline crusts and radial aggregates up to 3 mm developed in cavities and fractures in the porous quartz gangue with relicts of primary galena. It is associated with minor crystalline coatings of cerussite. The refined unit-cell parameters of pyromorphite from Chvojnica (for the hexagonal space group P63/m) are a 9.9750(2) Å, c 7.3569(2) Å and V 633.93(2) Å3. Except of dominant contents of Pb, P and Cl, only minor amounts of Ca (up to 0.10 apfu), Al (up to 0.05 apfu), Fe (up to 0.04 apfu), As (up to 0.05 apfu) and S (up to 0.02 apfu) were detected in studied pyromorphite. At the Hnilčík, pyromorphite occurs rarely in the cavities of the cavernous quartz-limonite gangue in the supergene zone of the Piata vein. It forms colourless to very light green prismatic crystals up to 2 mm in size, or crystalline aggregates associated with goethite, Mn oxides and malachite. The refined unit-cell parameters of pyromorphite from Hnilčík (for the hexagonal space group P63/m) are a 9.9484(15) Å, c 7.315(2) Å, V 627.0(2) Å3 (Ca-poor) and a 9.8983(6) Å, c 7.2589(8) Å, V 615.92(9) Å3 (Ca-rich). Pyromorphite from Hnilčík shows strong chemical zoning caused by variation of Pb and Ca contents, with outer parts of the crystals enriched in Ca. Contents of Ca are ranging between 0.09 to 0.96 apfu, with the atomic Pb/(Pb+Ca) ratio ranging from 0.98 to 0.81, which is close to the compositional boundary with phosphohedyphane. Interesting are also elevated concentrations of Cu reaching up to 0.07 apfu. Other minor elements detected in pyromorphite from Hnilčík are As (up to 0.12 apfu), Al, V and S (all up to 0.02 apfu).

Involvement of increased endoplasmic reticulum stress in the development of cataracts in BALB.NCT-Cpoxnct mice

The BALB.NCT-Cpoxnct is a mutant mouse model for hereditary cataracts. We previously uncovered that the primary cause of the cataracts of BALB.NCT-Cpoxnct is a mutation in the coproporphyrinogen oxidase (Cpox) gene. Because of the mutation, excessive coproporphyrin is accumulated in the BALB.NCT-Cpoxnct lens. In this study, we analyzed the changes in transcriptome and proteins in the lenses of 4- and 12-week-old BALB.NCT-Cpoxnct to further elucidate the molecular etiology of cataracts in this mouse strain. Transcriptome analysis revealed that endoplasmic reticulum (ER) stress was increased in the BALB.NCT-Cpoxnct lens that induced persistent activation of the PERK signaling pathway of the ER stress response. Also, levels of crystallin transcripts and proteins were reduced in the BALB.NCT-Cpoxnct lens. Analysis of proteins disclosed aggregation of crystallins and keratins prior to the manifestation of cataracts in 4-week-old BALB.NCT-Cpoxnct mice. At 12 weeks of age, insoluble crystallins were accumulated in the cataractous BALB.NCT-Cpoxnct lens. Overall, our data suggest the following sequence of events in the BALB.NCT-Cpoxnct lens: accumulated coproporphyrin induces the aggregation of proteins including crystallins. Aggregated proteins increase ER stress that, in turn, leads to the repression of global translation of proteins including crystallins. The decline in the molecular chaperone crystallin aggravates aggregation and insolubilization of proteins. This vicious cycle would eventually lead to cataracts in BALB.NCT-Cpoxnct.

Congenital cataract-causing mutation βB1-L116P is prone to amyloid fibrils aggregation and protease degradation with low structural stability

Congenital cataract, a common disease with lens opacification, causes blindness in the newborn worldwide and is mainly caused by abnormal aggregation of crystallin. As the main structural protein in the mammalian lens, βB1-crystallin has an important role in the maintenance of lens transparency. Recently, the L116P mutation in βB1-CRY was found in a Chinese family with congenital nuclear cataracts, while its underlying pathogenic mechanism remains unclear. In the current study, the βB1 wild-type protein was purified, and the mutated form, βB1-L116P, was examined for examining the effect on structural stability and susceptibility against environmental stresses. Our results reveal low solubility and structural stability of βB1-L116P at physiological temperature, which markedly impaired the protein structure and the oligomerization of βB1-crystallin. Under guanidine hydrochloride-induced denaturing conditions, βB1-L116P mutation perturbed the protein unfolding process, making it prone to amyloid fibrils aggregation. More importantly, the L116P mutation increased susceptibility of βB1-crystallin against UV radiation. βB1-L116P overexpression led to the formation of more serious intracellular aggresomes under UV radiation or oxidative stress. Furthermore, the βB1-L116P mutation increased the sensitivity to the proteolysis process. These results indicate that the low structural stability, susceptibility to amyloid fibrils aggregation, and protease degradation of βB1-L116P may contribute to cataract development and associated symptoms.

Defect of LSS Disrupts Lens Development in Cataractogenesis.

Congenital cataract is one of the leading causes of blindness in children worldwide. About one-third of congenital cataracts are caused by genetic defects. LSS, which encodes lanosterol synthase, is a causal gene for congenital cataracts. LSS is critical in preventing abnormal protein aggregation of various cataract-causing mutant crystallins; however, its roles in lens development remain largely unknown. In our study, we generated a mouse model harboring Lss G589S mutation, which is homologous to cataract-causing G588S mutation in human LSS. LssG589S/G589S mice exhibited neonatal lethality at postal day 0 (P0), whereas these mice showed severe opacity in eye lens. Also, we found that cataract was formed at E17.5 after we examined the opacity of embryonic lens from E13.5 to E18.5. Moreover, disrupted lens differentiation occurred at E14.5 prior to formation of the opacity of eye lens, shown as delayed differentiation of lens secondary fiber and disordered lens fiber organization. In addition, RNA-seq analysis indicated that cholesterol synthesis signaling pathways were significantly downregulated. Overall, our findings provide clear evidence that a mouse model harboring a homozygous Lss G589S mutation can recapitulate human congenital cataract. Our study points out that LSS functions as a critical determinant of lens development, which will contribute to better understanding LSS defects in cataractogenesis and developing therapies for cataracts.

Modeling of Hierarchical Cathodes for Li-Air Batteries with Improved Discharge Capacity

The non-aqueous Li-air battery is considered to be a promising energy source for electric-vehicles owing to its ultrahigh theoretical energy density. However, its commercialization is limited by the attained lower energy density value, which is mainly due to pore blockage and passivation which requires a more strategic design of the cathode. In this work, we have developed and validated a detailed one-dimensional continuum model of Li-Air battery that helps in examining the potential of hierarchical cathodes in guiding and enhancing the efficiency of ions transport and discharge product formation inside microstructures. The obtained results reveal the importance of reducing the tortuosity (shorten the path of oxygen transport) and increasing porosity at the airside of the hierarchical cathode, which improved discharge capacity at approximately 20.9 and 56%, respectively. The improved capacity is due to enhanced effective oxygen transport, impregnation of electrolyte, alignment of pores, and formation of permeable and low crystalline aggregates of Li2O2. Hence, strategies considering these insights can help in the design and fabrication of non-aqueous Li-air batteries with enhanced energy density and capacity.

Co-crystallized sucrose-soluble fiber matrix: Physicochemical and structural characterization

Dietary fibers are often under-consumed worldwide, even though their health benefits are already established in dietary guidelines, which recommend their daily intake of 25–30 g. Increasing the supply of fiber-enriched food products is a way to improve consumers’ daily intake. This study proposes the development of a mixed sucrose/erythritol/fiber matrix, particulate as a crystalline solid aggregate by the co-crystallization process to be used as a fiber-delivery ingredient in formulations with partial sugar reduction. The co-crystal was physicochemical and structurally characterized and compared to their individual components. The results indicated the formation of a sugar-based structure with fiber entrapped (29.8 g/100 g of co-crystals, db), presenting 5.33% of moisture content, 0,564 of water activity, and good flow properties. DSC thermogram displayed an endothermic transition peak at 187.31 °C, similar to the melting temperature of sucrose, suggesting the maintenance of the crystalline structure after co-crystallization and confirmed by X-ray diffraction and FTIR spectral profile. Morphological images showed small cluster agglomerates with a covering layer on structure, indicating the presence of the fiber in the matrix. Thus, co-crystallization constitutes an alternative process for the production of particulate crystalline solid containing fiber, being a great alternative to food ingredients in less sugar-added and fiber-enriched products.

Issue Information

The FEBS JournalVolume 288, Issue 20 p. 5783-5785 Issue Cover & InformationFree Access Issue Information First published: 18 October 2021 https://doi.org/10.1111/febs.15414AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Graphical Abstract Cover Illustration Challenges and outlook in studying the structural biology of crystallin aggregation, reviewed by Khandekar Jishan Bari in pages 5888–5902 of this issue. Volume288, Issue20October 2021Pages 5783-5785 RelatedInformation

Analysis of amyloid-like secondary structure in the Cryab-R120G knock-in mouse model of hereditary cataracts by two-dimensional infrared spectroscopy.

αB-crystallin is a small heat shock protein that forms a heterooligomeric complex with αA-crystallin in the ocular lens. It is also widely distributed in tissues throughout the body and has been linked with neurodegenerative diseases such as Alzheimer’s, where it is associated with amyloid fibrils. Crystallins can form amorphous aggregates in cataracts as well as more structured amyloid-like fibrils. The arginine 120 to glycine (R120G) mutation in αB-crystallin (Cryab-R120G) results in high molecular weight crystallin protein aggregates and loss of the chaperone activity of the protein in vitro, and it is associated with human hereditary cataracts and myopathy. Characterizing the amorphous (unstructured) versus the highly ordered (amyloid fibril) nature of crystallin aggregates is important in understanding their role in disease and important to developing pharmacological treatments for cataracts. We investigated protein secondary structure in wild-type (WT) and Cryab-R120G knock-in mutant mouse lenses using two-dimensional infrared (2DIR) spectroscopy, which has been used to detect amyloid-like fibrils in human lenses and measure UV radiation-induced changes in porcine lenses. Our goal was to compare the aggregated proteins in this mouse lens model to human lenses and evaluate the protein structural relevance of the Cryab-R120G knock-in mouse model to general age-related cataract disease. In the 2DIR spectra, amide I diagonal peak frequencies were red-shifted to smaller wavenumbers in mutant mouse lenses as compared to WT mouse lenses, consistent with an increase in ordered secondary structure. The cross peak frequency and intensity indicated the presence of amyloid in the mutant mouse lenses. While the diagonal and cross peak changes in location and intensity from the 2DIR spectra indicated significant structural differences between the wild type and mutant mouse lenses, these differences were smaller than those found in human lenses; thus, the Cryab-R120G knock-in mouse lenses contain less amyloid-like secondary structure than human lenses. The results of the 2DIR spectroscopy study confirm the presence of amyloid-like secondary structure in Cryab-R120G knock-in mice with cataracts and support the use of this model to study age-related cataract.

Bowls, vases and goblets\u2014the microcrockery of polymer and nanocomposite morphology revealed by two-photon optical tomography

On the >1 µm scale the morphology of semicrystalline plastics like polyethylene or Nylon features spherulites, “shish-kebabs”, cylinddrites and other crystalline aggregates which strongly affect mechanical and other material properties. Current imaging techniques give only a 2D picture of these objects. Here we show how they can be visualized in 3D using fluorescent labels and confocal microscopy. As a result, we see spherulites in 3D, both in neat polymers and their nanocomposites, and observe how unevenly nanoparticles and other additives are distributed in the material. Images of i-polypropylene and biodegradable poly(lactic acid) reveal previously unsuspected morphologies such as “vases” and “goblets”, nonspherical “spherulites” and, unexpectedly, “shish-kebabs” grown from quiescent melt. Also surprisingly, in nanocomposite sheets spherulite nucleation is seen to be copied from one surface to another, mediated by crystallization-induced pressure drop and local melt-flow. These first results reveal unfamiliar modes of self-assembly in familiar plastics and open fresh perspectives on polymer microstructure.

Structure impact on photodynamic therapy and cellular contrasting functions of colloids constructed from dimeric Au(I) complex and hexamolybdenum clusters

Electrostatically driven self-assembly of [Au2L2]2+ (L is cyclic PNNP ligand) with [{Mo6I8}(L')6]2− (L' = I−, CH3COO−) in aqueous solutions is introduced as facile route for combination of therapeutic and cellular contrasting functions within heterometallic colloids (Mo6-Au2). The nature of L' affects the size and aggregation behavior of crystalline Mo6-Au2 aggregates, which in turn affect the luminescence of the cluster units incorporated into Mo6-Au2 colloids. The spin trap facilitated electron spin resonance spectroscopy technique indicates that the level of ROS generated by Mo6-Au2 colloids is also affected by their size. Both (L' = I−, CH3COO−) Mo6-Au2 colloids undergo cell internalization, which is enhanced by their assembly with poly-DL-lysine (PL) for L' = CH3COO−, but remains unchanged for L' = I−. The colloids PL-Mo6-Au2 (L' = CH3COO−) are visualized as huge crystalline aggregates both outside and inside the cell cytoplasm by confocal microscopy imaging of the incubated cells, while the smaller sized (30–50 nm) PL-Mo6-Au2 (L' = I−) efficiently stain the cell nuclei. Quantitative colocalization analysis of PL-Mo6-Au2 (L' = CH3COO−) in lysosomal compartments points to the fast endo-lysosomal escape of the colloids followed by their intracellular aggregation. The cytotoxicity of PL-Mo6-Au2 differs from that of Mo6 and Au2 blocks, predominantly acting through apoptotic pathway. The photodynamic therapeutic effect of the PL-Mo6-Au2 colloids on the cancer cells correlates with their intracellular trafficking and aggregation.

Search for Crystalline Species of Urinary Stones by Patients in the Region of Tissemsilt, Algeria

Urinary stones are among the most common diseases in the world and in Algeria as well, because it is a complex and multifactorial disease. The saturation of solutes in the urine is considered as the main stage of the deposition of crystals and their rapid growth and aggregation lead to the formation of stones in different places of the urinary system. It is the consequence of excessive urinary supersaturation causing renal complications such as lithiasis, nephrocalcinosis, acute or chronic renal failure which may progress to the terminal stage. The purpose of the study was to identify the most common different forms of crystals in the urine of patients for further measures to prevent more serious complications of crystalluria. Materials and methods. The study focused on all lithiasis patients of the age group "from 20 years to 84 years". Three-day urine samples were collected at different urology departments which were referred by urologists, during the period from February 06, 2020 to March 21, 2020. Being the best method, crystalluria was used to determine the types of crystals, their number and their growth. Three criteria must be met for the study of crystalluria to be clinically interpretable. They are the choice of patients according to their metabolic state; how long urine is stored after it is released, and the storage temperature. Results and discussion. Thanks to this study it was possible to characterize many types of crystals, including calcium oxalates, in particular monohydrate, which is considered as a risk factor for stone formation. Also, the urinary acid crystals indicate a specific environmental pattern in many patients. In addition to the calcium phosphate crystals resulting from microbial infections, the results showed pure crystalline aggregates which will inevitably lead to lithiasis. The microscopic examination of patient urine samples is the preferred method for optimal patient assurance with the cooperation of therapists and doctors in addition to the epidemiological study. Conclusion. The relatively high rate of recurrent lithiasis illustrates the current limits of preventive measures which can be penalized by the lack of patient attendance but whose reduced effectiveness primarily suggests a lack of knowledge of one or more fundamental determinants of the lithogenic process. The experimental part showed a diversity of crystals in the urine of patients, pure calcium oxalate monohydrate, which was noticed in the majority of the subjects analyzed. The detection, in crystalluria, of a single crystal of whewellite can therefore be considered as a marker for hyperoxaluria. Weddellite was more common in the urine of subjects under analysis

A Potential Role for Fructosamine-3-Kinase in Cataract Treatment.

Cataracts are the major cause of blindness worldwide, largely resulting from aging and diabetes mellitus. Advanced glycation end products (AGEs) have been identified as major contributors in cataract formation because they alter lens protein structure and stability and induce covalent cross-linking, aggregation, and insolubilization of lens crystallins. We investigated the potential of the deglycating enzyme fructosamine-3-kinase (FN3K) in the disruption of AGEs in cataractous lenses. Macroscopic changes of equine lenses were evaluated after ex vivo intravitreal FN3K injection. The mechanical properties of an equine lens pair were evaluated after treatment with saline and FN3K. AGE-type autofluorescence (AF) was measured to assess the time-dependent effects of FN3K on glycolaldehyde-induced AGE-modified porcine lens fragments and to evaluate its actions on intact lenses after in vivo intravitreal FN3K injection of murine eyes. A potential immune response after injection was evaluated by analysis of IL-2, TNFα, and IFNγ using an ELISA kit. Dose- and time-dependent AF kinetics were analyzed on pooled human lens fragments. Furthermore, AF measurements and a time-lapse of macroscopic changes were performed on intact cataractous human eye lenses after incubation with an FN3K solution. At last, AF measurements were performed on cataractous human eyes after crossover topical treatment with either saline- or FN3K-containing drops. While the lenses of the equine FN3K-treated eyes appeared to be clear, the saline-treated lenses had a yellowish-brown color. Following FN3K treatment, color restoration could be observed within 30 min. The extension rate of the equine FN3K-treated lens was more than twice the extension rate of the saline-treated lens. FN3K treatment induced significant time-dependent decreases in AGE-related AF values in the AGE-modified porcine lens fragments. Furthermore, in vivo intravitreal FN3K injection of murine eyes significantly reduced AF values of the lenses. Treatment did not provoke a systemic immune response in mice. AF kinetics of FN3K-treated cataractous human lens suspensions revealed dose- and time-dependent decreases. Incubation of cataractous human eye lenses with FN3K resulted in a macroscopic lighter color of the cortex and a decrease in AF values. At last, crossover topical treatment of intact human eyes revealed a decrease in AF values during FN3K treatment, while showing no notable changes with saline. Our study suggests, for the first time, a potential additional role of FN3K as an alternative treatment for AGE-related cataracts.

Nanostructured Polymer Composite Electrolytes with Self-Assembled Polyoxometalate Networks for Proton Conduction

Nanostructured Polymer Composite Electrolytes with Self-Assembled Polyoxometalate Networks for Proton Conduction

Development of a potent embryonic chick lens model for studying congenital cataracts in vivo

Congenital cataracts are associated with gene mutations, yet the underlying mechanism remains largely unknown. Here we reported an embryonic chick lens model that closely recapitulates the process of cataract formation. We adopted dominant-negative site mutations that cause congenital cataracts, connexin, Cx50E48K, aquaporin 0, AQP0R33C, αA-crystallin, CRYAA R12C and R54C. The recombinant retroviruses containing these mutants were microinjected into the occlusive lumen of chick lenses at early embryonic development. Cx50E48K expression developed cataracts associated with disorganized nuclei and enlarged extracellular spaces. Expression of AQP0R33C resulted in cortical cataracts, enlarged extracellular spaces and distorted fiber cell organization. αA crystallin mutations distorted lens light transmission and increased crystalline protein aggregation. Together, retroviral expression of congenital mutant genes in embryonic chick lenses closely mimics characteristics of human congenital cataracts. This model will provide an effective, reliable in vivo system to investigate the development and underlying mechanism of cataracts and other genetic diseases.

Мінералогічні особливості відновлених окатишів Північного гірничозбагачувального комбінату (Криворізький басейн)

The advantages of reduced iron ore pellets over oxidized ones have been considered. The chemical and physical parameters of the primary material have been given: iron ore (magnetite) concentrate (iron content is 67.30 mass %; particle size distribution is 97.0 % of 0.056 mm fraction), bentonite (montmorilonit content is 70.43 mass %; particle size distribution is 94.5% of 0.056 mm fraction), ground coke. The course of experiments has been described. The zonal structure of the obtained pellets has been characterized: the central zone is composed of hematite with relics of magnetite; intermediate one contains magnetite particles with inclusions of hematite; peripheral zone includes subidiomorphic crystals of magnetite and their dendritic aggregates. The bentonite component in the central and intermediate zones retained a crypto-crystalline structure, in the peripheral one it had been transformed into a crystalline aggregate of garnet and pyroxene. Emphasis is placed on the need to verify the impact of various indicators of temperature, firing time, quantitative ratios of charge components, mineral and chemical composition of the cementing material on mineralogical transformations.

Chemical Properties Determine Solubility and Stability in βγ-Crystallins of the Eye Lens.

βγ-Crystallins are the primary structural and refractive proteins found in the vertebrate eye lens. Because crystallins are not replaced after early eye development, their solubility and stability must be maintained for a lifetime, which is even more remarkable given the high protein concentration in the lens. Aggregation of crystallins caused by mutations or post-translational modifications can reduce crystallin protein stability and alter intermolecular interactions. Common post-translational modifications that can cause age-related cataracts include deamidation, oxidation, and tryptophan derivatization. Metal ion binding can also trigger reduced crystallin solubility through a variety of mechanisms. Interprotein interactions are critical to maintaining lens transparency: crystallins can undergo domain swapping, disulfide bonding, and liquid-liquid phase separation, all of which can cause opacity depending on the context. Important experimental techniques for assessing crystallin conformation in the absence of a high-resolution structure include dye-binding assays, circular dichroism, fluorescence, light scattering, and transition metal FRET.

HABS‐Silicate Controlled Synthesis of Worm‐Like Calcite via Orientated Attachment

AbstractWorm‐like calcite crystals were successfully synthesized by hydrothermal method in heavy alkylbenzene sulfonate (HABS)‐ silicate hybrid aqueous system at 45 °C for 48 h. The result indicated that HABS can affect step/kink sites on the growth face of {104} calcite by alternating Ca2+ or CO32− layers, resulting a slight rotation or stacking faults of the subunits, which lead to the worm shape of crystalline aggregates by elongating parallel to the c‐axis of the rhombohedral lattice. The overlapping worm structures were obtained with the synergistic effect of HABS and silicate, which presents an additives‐mediated crystallographically self‐assembly of worm‐like units and also the inheritance of orientated attachment with rhombohedral calcite habits.

Stellate Genes and the piRNA Pathway in Speciation and Reproductive Isolation of Drosophila melanogaster.

One of the main conditions of the species splitting from a common precursor lineage is the prevention of a gene flow between diverging populations. The study of Drosophila interspecific hybrids allows to reconstruct the speciation mechanisms and to identify hybrid incompatibility factors that maintain post-zygotic reproductive isolation between closely related species. The regulation, evolution, and maintenance of the testis-specific Ste-Su(Ste) genetic system in Drosophila melanogaster is the subject of investigation worldwide. X-linked tandem testis-specific Stellate genes encode proteins homologous to the regulatory β-subunit of protein kinase CK2, but they are permanently repressed in wild-type flies by the piRNA pathway via piRNAs originating from the homologous Y-linked Su(Ste) locus. Derepression of Stellate genes caused by Su(Ste) piRNA biogenesis disruption leads to the accumulation of crystalline aggregates in spermatocytes, meiotic defects and male sterility. In this review we summarize current data about the origin, organization, evolution of the Ste-Su(Ste) system, and piRNA-dependent regulation of Stellate expression. The Ste-Su(Ste) system is fixed only in the D. melanogaster genome. According to our hypothesis, the acquisition of the Ste-Su(Ste) system by a part of the ancient fly population appears to be the causative factor of hybrid sterility in crosses of female flies with males that do not carry Y-linked Su(Ste) repeats. To support this scenario, we have directly demonstrated Stellate derepression and the corresponding meiotic disorders in the testes of interspecies hybrids between D. melanogaster and D. mauritiana. This finding embraces our hypothesis about the contribution of the Ste-Su(Ste) system and the piRNA pathway to the emergence of reproductive isolation of D. melanogaster lineage from initial species.

The structural biology of crystallin aggregation: challenges and outlook.

Crystallin aggregation is characterized by light scattering of large molecular aggregates due to their phase separation in the lens. Low-resolution biophysical studies using multiple techniques have characterized the folding, stability, binding, and aggregation of crystallins in the past but with limited access to their structure, dynamics, and interactions. In this Viewpoint, three schools of experimental structural biology, that is, X-ray crystallography, solution and solid-state NMR spectroscopy, and cryo-electron microscopy, combine to provide atomic resolution details of native crystallins, soluble oligomers, and insoluble amyloid fibrils and amorphous aggregates. Computational structural biology provides additional details on crystallin dynamics and the crucial intercrystallin interactions in these events. Our current understanding of the diverse structural biology of crystallins is consistent with multiple pathways of protein aggregation for different structural intermediates. This Viewpoint combines our efforts with those of others to elucidate the recent progress in these high-resolution studies and proposes an integrated structural biology approach to resolve the complex lens interactome. Overall, I discuss the outstanding questions and evaluate the experimental and theoretical caveats in the field.