The origin and evolution of new microRNAs (miRNAs) is important because they can impact the transcriptome broadly. As miRNAs can potentially emerge constantly and rapidly, their rates of birth and evolution have been extensively debated. However, most new miRNAs identified appear not to be biologically significant. After an extensive search, we identified 12 new miRNAs that emerged de novo in Drosophila melanogaster in the last 4 million years (Myrs) and have been evolving adaptively. Unexpectedly, even though they are adaptively evolving at birth, more than 94% of such new miRNAs disappear over time. They provide selective advantages, but only for a transient evolutionary period. After 30 Myrs, all surviving miRNAs make the transition from the adaptive phase of rapid evolution to the conservative phase of slow evolution, apparently becoming integrated into the transcriptional network. During this transition, the expression shifts from being tissue-specific, predominantly in testes and larval brain/gonads/imaginal discs, to a broader distribution in many other tissues. Interestingly, a measurable fraction (20–30%) of these conservatively evolving miRNAs experience “evolutionary rejuvenation” and begin to evolve rapidly again. These rejuvenated miRNAs then start another cycle of adaptive – conservative evolution. In conclusion, the selective advantages driving evolution of miRNAs are themselves evolving, and sometimes changing direction, which highlights the regulatory roles of miRNAs.

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Copper I 7400 Plasmonic Cu2-xS Nanocrystals: Optical and Structural Properties of Copper--Deficient Copper(I) Sulfides. -Cu 2-x S (x = 1, 0.2, 0.03) nanocrystals are prepared by three different convenient and environmental benign techniques based on sonoelectrochemical, hydrothermal, and solventless thermolysis methods using CuSO4 as starting material. The samples are characterized by powder XRD, TEM, UV/VIS, and NIR spectroscopy. The compositions of the nanocrystals ranges from CuS to Cu1.97S by adjusting the reduction potential in the sonoelectrochemical method, from CuS to Cu 1.97 S by adjusting the pH values in the hydrothermal method, and from Cu1.8S to Cu1.97S in the thermolysis method. Cu2S is thermodynamically unstable under ambient conditions, compared to the Cu2-xS phase. All Cu2-xS nanocrystals show a blue shift in the band gap absorption compared to bulk Cu2-xS and are of direct band gap type, different from previously reported experimental results. Cu 2-x S nanocrystals show a plasmonic absorption, which depends on the carrier concentration. -(ZHAO, Y.; PAN, H.; LOU, Y.; QIU, X.; ZHU*, J.; BURDA, C.; J.

Food web and gene regulatory networks (GRNs) are large biological networks, both of which can be analyzed using the May–Wigner theory. According to the theory, networks as large as mammalian GRNs would require dedicated gene products for stabilization. We propose that microRNAs (miRNAs) are those products. More than 30% of genes are repressed by miRNAs, but most repressions are too weak to have a phenotypic consequence. The theory shows that (i) weak repressions cumulatively enhance the stability of GRNs, and (ii) broad and weak repressions confer greater stability than a few strong ones. Hence, the diffuse actions of miRNAs in mammalian cells appear to function mainly in stabilizing GRNs. The postulated link between mRNA repression and GRN stability can be seen in a different light in yeast, which do not have miRNAs. Yeast cells rely on non-specific RNA nucleases to strongly degrade mRNAs for GRN stability. The strategy is suited to GRNs of small and rapidly dividing yeast cells, but not the larger mammalian cells. In conclusion, the May–Wigner theory, supplanting the analysis of small motifs, provides a mathematical solution to GRN stability, thus linking miRNAs explicitly to ‘developmental canalization’.