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The nucleolus is the largest nuclear sub-compartment in which the early steps of ribosome biogenesis take place. It also plays an essential role in the assembly and function of non-ribosomal ribonucleoprotein (RNP) complexes, controls cell cycle progression and senses environmental stress. The spatial organization and dynamics of nucleolar proteins and RNA is regulated at different structural levels, which finally determine nucleolar architecture. The intimate link between nucleolar structure and function is reflected by transcription-dependent changes in nucleolus-associated chromatin, overall morphological alterations in response to external cues, and the liquid droplet-like behavior of nucleolar compartments. Here we provide a concise overview of the latest studies which integrate novel trends in nucleolar architecture research into the context of cell biology. [ABSTRACT FROM AUTHOR]

Ion implantation has been a key technology for the controlled surface modification of materials in microelectronics and generally, for tribology, biocompatibility, corrosion resistance and many more. To form shallow junctions in Ge is a challenging task. In this work the formation and accumulation of shallow damage profiles was studied by in-situ spectroscopic ellipsometry (SE) for the accurate tracking and evaluation of void and damage fractions in crystalline Ge during implantation of 200-keV Sb + ions with a total fluence up to 1016 cm−2 and an ion flux of 2.1 × 1012 cm−2s−1. The consecutive stages of damage accumulation were identified using optical multi-layer models with quantitative parameters of the thickness of modified layers as well as the volume fractions of amorphized material and voids. The effective size of damaged zones formed from ion tracks initiated by individual bombarding ions can be estimated by numerical simulation compared with the dynamics of damage profiles measured by ion beam analysis and ellipsometry. According to our observations, the formation of initial partial disorder was followed by complete amorphization and void formation occurring at the fluence of about 1 × 1015 cm−2, leading to a high volume fraction of voids and a modified layer thickness of ≈200 nm by the end of the irradiation process. This agrees with the results of numerical simulations and complementary scanning electron microscopy (SEM) measurements. In addition, we found a quasi-periodic time dependent behavior of amorphization and void formation represented by alternating accelerations and decelerations of different reorganization processes, respectively. For the understanding and prevention of adverse void formation and for controlled evolution of subsurface nanocavities or cellular surface texture the in-situ monitoring of the dynamics of structural damage accumulation by the developed SE method is essential. [ABSTRACT FROM AUTHOR]

The nucleolus is the site of ribosome biogenesis and forms around the actively transcribed ribosomal RNA (rRNA) genes. However, the nucleolus is also implicated in cell cycle regulation, tumour suppression and chromosome segregation and nucleolar disfunction is linked to a wide range of human diseases. Interestingly, the nucleolus is also required for genome reprogramming and the establishment of heterochromatin in the mammalian embryo. Mammalian oocytes contain a subnuclear structure that is believed to be the precursor of the functional nucleolus, the Nucleolar Precursor Body (NPB). But the NPB is also required for the organisation of the zygotic heterochromatin and the establishment of pluripotency. We found that disruption of the mouse Upstream Binding Factor (UBF (UBTF)) gene caused disassembly of somatic nucleoli and the accumulation of the key rRNA gene transcription factors into dense subnuclear foci resembling NPBs. Here we show that UBF deletion causes the rRNA genes to collapse onto their centromere-proximal chromosomal sites spatially distinct from NPB-like structures, and that these structures contain rRNA gene transcription factors but not all nucleolar proteins. We further find that embryonic NPBs and their surrounding heterochromatin are both disrupted in UBF-null mouse embryos. These embryos also display subnuclear foci containing the rRNA gene transcription factors and arrest development before completing the forth cleavage division. The data suggest that the rRNA gene transcription factors have an intrinsic ability to interact and form a discrete nuclear compartment even in the absence of any rRNA gene activity and that the formation or maintenance of the zygotic NPB and surrounding heterochromatin requires UBF. [ABSTRACT FROM AUTHOR]

The good control of the n -type doping is a key issue for the fabrication of efficient devices based on ε-Ga 2 O 3 epilayers. In this work we studied the possibility of doping the ε-Ga 2 O 3 thin films, epitaxially grown on c -oriented sapphire by metal-organic chemical vapor deposition, by means of a post-deposition treatment. For the first time, the n -type doping was achieved by depositing a tin-rich SnO 2 film on top of the ε-Ga 2 O 3 layer and keeping this bi-layer system for 4 h at a temperature of 600 °C in an evacuated furnace. The diffusion of Sn atoms into the ε-Ga 2 O 3 film is evidenced by time-of-flight secondary-ion mass spectrometry depth profiles. Room-temperature resistivity of the order of 1 Ω•cm is obtained and the electrical characterization revealed a conduction mechanism based on variable range hopping, according to the Mott's model. [Display omitted] [ABSTRACT FROM AUTHOR]