Piwi family proteins are essential for germline development and bind piwi-interacting RNAs (piRNAs 1 2 3). The grandchildless gene aub of Drosophila melanogaster encodes the piRNA-binding protein Aub that is essential for formation of primordial germ cells (PGCs) 4. Here we report that mouse, Xenopus laevis and Drosophila melanogaster Piwi family proteins contain symmetrical dimethylarginines (sDMAs). We find that Piwi proteins are expressed in X. laevis oocytes and we identify numerous X. laevis piRNAs. We report that the Drosophila homolog of protein methyltransferase 5 (dPRMT5, csul/dart5), which is also the product of a grandchildless gene 5, 6, is required for arginine methylation of Drosophila Piwi, Ago3 and Aub proteins, in vivo. Loss of dPRMT5 activity leads to reduction of piRNAs and in particular of Ago3 and Aub protein levels and accumulation of retrotransposons in the Drosophila ovary. Our studies explain the relationship between aub and dPRMT5 (csul/dart5) genes by demonstrating that dPRMT5 is the enzyme that methylates Aub. Our findings underscore the significance of sDMA modification of Piwi proteins in the germline and suggest an interacting pathway of genes that are required for piRNA function and PGC specification.

No abstract

A systematic study was conducted into the use of metal-assisted chemical etching (MacEtch) to fabricate vertical Si microwire arrays, with several models being studied for the efficient redox reaction of reactants with silicon through a metal catalyst by varying such parameters as the thickness and morphology of the metal film. By optimizing the MacEtch conditions, high-quality vertical Si microwires were successfully fabricated with lengths of up to 23.2 μm, which, when applied in a solar cell, achieved a conversion efficiency of up to 13.0%. These solar cells also exhibited an open-circuit voltage of 547.7 mV, a short-circuit current density of 33.2 mA/cm2, and a fill factor of 71.3% by virtue of the enhanced light absorption and effective carrier collection provided by the Si microwires. The use of MacEtch to fabricate high-quality Si microwires therefore presents a unique opportunity to develop cost-effective and highly efficient solar cells.

We demonstrate novel all-back-contact Si nanohole solar cells via the simple direct deposition of molybdenum oxide (MoOx) and lithium fluoride (LiF) thin films as dopant-free and selective carrier contacts (SCCs). This approach is in contrast to conventionally used high-temperature thermal doping processes, which require multistep patterning processes to produce diffusion masks. Both MoOx and LiF thin films are inserted between the Si absorber and Al electrodes interdigitatedly at the rear cell surfaces, facilitating effective carrier collection at the MoOx/Si interface and suppressed recombination at the Si and LiF/Al electrode interface. With optimized MoOx and LiF film thickness as well as the all-back-contact design, our 1 cm(2) Si nanohole solar cells exhibit a power conversion efficiency of up to 15.4%, with an open-circuit voltage of 561 mV and a fill factor of 74.6%. In particular, because of the significant reduction in Auger/surface recombination as well as the excellent Si-nanohole light absorption, our solar cells exhibit an external quantum efficiency of 83.4% for short-wavelength light (∼400 nm), resulting in a dramatic improvement (54.6%) in the short-circuit current density (36.8 mA/cm(2)) compared to that of a planar cell (23.8 mA/cm(2)). Hence, our all-back-contact design using MoOx and LiF films formed by a simple deposition process presents a unique opportunity to develop highly efficient and low-cost nanostructured Si solar cells.

Recent studies have uncovered an unexpected relationship between factors that are essential for germline development in Drosophila melanogaster: the arginine protein methyltransferase 5 (dPRMT5/Csul/Dart5) and its cofactor Valois, methylate the Piwi family protein Aub, enabling it to bind Tudor. The RNA helicase Vasa is another essential protein in germline development. Here, we report that mouse (mouse Vasa homolog), Xenopus laevis, and D. melanogaster Vasa proteins contain both symmetrical and asymmetrical dimethylarginines. We find that dPRMT5 is required for the production of sDMAs of Vasa in vivo. Furthermore, we find that the mouse Vasa homolog associates with Tudor domain-containing proteins, Tdrd1 and Tdrd6, as well as the Piwi proteins, Mili and Miwi. Arginine methylation is thus emerging as a conserved and pivotal posttranslational modification of proteins that is essential for germline development.Germline specification is an essential process for all sexually reproducing organisms. In Drosophila melanogaster, germline development is initiated by the formation of the germ cell precursors, pole cells, which are induced through the activity of maternally inherited, cytoplasmic determinants deposited in the pole plasm (also known as germ plasm) at the posterior pole of the oocyte (1-3). Genetic studies have identified maternal genes (often referred to as posterior group or grandchild-less genes) that are required for germ cell specification and the protein or RNA products of these genes are invariably concentrated in the pole plasm (2-4). Among these genes are aub (5); csul/dart5 (the D. melanogaster homolog of protein methyltransferase 5, dPRMT5) (6, 7) and its cofactor valois (8), tudor (9, 10, 11), and vasa (12, 13).Vasa encodes an ϳ65-kDa DEAD-box RNA helicase whose expression is exclusively restricted to the germ cell lineage (12, 13). Vasa binds RNA, and this activity is required for germ cell formation but not for localization to the pole plasm (14). Vasa binds to eukaryotic initiation factor 5B, and this interaction is required for germ cell development (15). A proposed function for Vasa is that it regulates the translation of target mRNAs involved in germ cell establishment such as oskar and nanos, and oogenesis such as gurken (15)(16)(17)(18)(19) DDX4) expression is also restricted to the germ cell lineage (26) and loss of MVH protein function causes a deficiency in the proliferation and differentiation of spermatocytes, leading to male sterility (27).Protein arginine methylation is an important post-translational modification that is mediated by two types of protein methyltransferases (PRMTs). Type I enzymes (such as PRMT1) catalyze asymmetric dimethylation of arginines (aDMA) and type II enzymes (such as PRMT5) catalyze symmetric arginine dimethylation (sDMA) (Fig. 1C) (28, 29). sDMA modifications occur in sequence motifs composed of arginines flanked by glycines (GRG) or alanines (GRA or ARG) that are often found as repeats, whereas aDMAs frequently occur in repeating "RGG" sequences (28,29)...

We report a neutral-colored transparent c-Si substrate using a 200-mm-thick c-Si wafer, which is known to be opaque. The transparent c-Si substrate shows a completely neutral color, similar to glass without a transmission cut-on wavelength. In addition, the transmittance of the transparent c-Si substrate is systematically tuned under the full solar spectrum. As a representative application, the transparent solar cells fabricated with the substrate developed in this study show a power conversion efficiency of up to 12.2%.

No abstract

We developed a unique nano- and microwire hybrid structure by selectively modifying only the tops of microwires using metal-assisted chemical etching. The proposed nano/micro hybrid structure not only minimizes surface recombination but also absorbs 97% of incident light under AM 1.5G illumination, demonstrating outstanding light absorption compared to that of planar (59%) and microwire arrays (85%). The proposed hybrid solar cells with an area of 1 cm(2) exhibit power conversion efficiencies (Eff) of up to 17.6% under AM 1.5G illumination. In particular, the solar cells show a high short-circuit current density (Jsc) of 39.5 mA cm(-2) because of the high light-absorbing characteristics of the nanostructures. This corresponds to an approximately 61.5% and 16.5% increase in efficiency compared to that of a planar silicon solar cell (Eff = 10.9%) and a microwire solar cell (Eff = 15.1%), respectively. Therefore, we expect the proposed hybrid structure to become a foundational technology for the development of highly efficient radial junction solar cells.