A small RNA response at DNA ends in Drosophila

Small RNAs have been implicated in numerous cellular processes, including effects on chromatin structure and the repression of transposons. We describe the generation of a small RNA response at DNA ends in Drosophila that is analogous to the recently reported double-strand break (DSB)-induced RNAs or Dicer- and Drosha-dependent small RNAs in Arabidopsis and vertebrates. Active transcription in the vicinity of the break amplifies this small RNA response, demonstrating that the normal messenger RNA contributes to the endogenous small interfering RNAs precursor. The double-stranded RNA precursor forms with an antisense transcript that initiates at the DNA break. Breaks are thus sites of transcription initiation, a novel aspect of the cellular DSB response. This response is specific to a double-strand break since nicked DNA structures do not trigger small RNA production. The small RNAs are generated independently of the exact end structure (blunt, 3′- or 5′-overhang), can repress homologous sequences in trans and may therefore—in addition to putative roles in repair—exert a quality control function by clearing potentially truncated messages from genes in the vicinity of the break

The Spectral Properties of Pitted Impact Deposits on Vesta as Seen by the Dawn VIR Instrument

Pitted impact deposits (PIDs) on Vesta have been shown to exhibit distinct spectral characteristics with respect to their surrounding host deposits and other typical Vestan areas regarding the first major pyroxene absorption near 0.9 μm. The PIDs, especially those in the ejecta blanket of the large crater Marcia, show higher reflectance and pyroxene band strength with respect to their impact deposit surroundings. This study complements the spectral characterization of the PIDs on Vesta with Visible and Infrared Spectrometer observations obtained by NASA's Dawn mission. In particular, we focus on the second major pyroxene absorption near 1.9 μm. We analyze nine PIDs in the ejecta blanket of the crater Marcia, as well as PIDs within the crater-fill deposits of the craters Marcia, Cornelia, and Licinia. We find that the second pyroxene absorption behaves in similar ways as the first major pyroxene absorption. The PIDs in Marcia's ejecta blanket show higher reflectance and pyroxene band strength with respect to their immediate impact deposit surroundings. The PIDs present in the crater-fill deposits of Marcia, Cornelia, and Licinia, however, do not show such spectral characteristics. This is also consistent with previous observations of the first pyroxene absorption band. Based on the experimental results of other studies, we speculate that the observed spectral distinctness arises from an oxidation process in the interior of impact deposits, where Fe cations migrate within their host pyroxene grains. Thus, the surfaces of (melt-bearing) impact deposits might be different from their interiors, apart from space-weathering effects

Spectral and Petrographic Properties of Inclusions in Carbonaceous Chondrites and Comparison with In Situ Images from Asteroid Ryugu

We imaged a set of carbonaceous chondrites from the CM2, CO3, CV3, and CK4 groups using the qualification model of MasCam, the camera on board the asteroid lander MASCOT, which touched down on asteroid Ryugu in 2018 October. A CI1 meteorite was also imaged but excluded from the analysis due to prominent terrestrial weathering. Following the methods used to image the rock on Ryugu, we placed a total of 14 meteorites approximately 20 cm in front of the camera to achieve a spatial resolution of about 0.2 mm per pixel and illuminated the samples with onboard light-emitting diodes of four different colors in the visible wavelength range. We mapped bright and dark inclusions within the meteorites and derived the inclusion brightness relative to the matrix in the red light, the relative spectral slope of each inclusion, the inclusion size frequency distribution and the matrix volume abundance. We find that the meteorite groups overlap within these parameters, but individual samples, as well as individual inclusions, can have deviating values. Terrestrial weathering appears to have no systematic influence on these parameters. Relating our analysis to the inclusions found in the rock on Ryugu, we find that the spectral parameters of Ryugu's inclusions fit well in the parameter space of the carbonaceous chondrites. Compared with the most common types of carbonaceous chondrites, Ryugu's rock has larger inclusions (mean diameter: 0.63 ± 0.91 mm) and a higher upper limit to the matrix abundance (92.4 vol%)

Assessing the Effects of Heating Vesta-Like Material on its Spectral Characteristics

We investigate the spectral behavior of Vesta-like materials upon heating to different temperatures for different time spans in order to understand the spectral characteristic of the pitted terrains' material on Vesta