Homeotic proteins participate in the function of human-DNA replication origins

Recent evidence points to homeotic proteins as actors in the crosstalk between development and DNA replication. The present work demonstrates that HOXC13, previously identified as a new member of human DNA replicative complexes, is a stable component of early replicating chromatin in living cells: it displays a slow nuclear dynamics due to its anchoring to the DNA minor groove via the arginine-5 residue of the homeodomain. HOXC13 binds in vivo to the lamin B2 origin in a cell-cycle-dependent manner consistent with origin function; the interaction maps with nucleotide precision within the replicative complex. HOXC13 displays in vitro affinity for other replicative complex proteins; it interacts also in vivo with the same proteins in a cell-cycle-dependent fashion. Chromatin-structure modifying treatments, disturbing origin function, reduce also HOXC13–origin interaction. The described interactions are not restricted to a single origin nor to a single homeotic protein (also HOXC10 binds the lamin B2 origin in vivo). Thus, HOX complexes probably contribute in a general, structure-dependent manner, to origin identification and assembly of replicative complexes thereon, in presence of specific chromatin configurations.     

Pigeon navigation: Time course of olfactory signal processing and dependence on access to fresh environmental air

Summary 16 releases, centrally symmetrical by pairs and involving distances of displacement from 25 to 172 km, were conducted with homing pigeons pre-treated in different ways: FIL birds were, until few minutes before release, confined to containers ventilated with ambient air that had passed through filters consisting of activated charcoal. NOFIL birds were confined to containers ventilated with unfiltered air, either from departure at the loft onwards (4 experiments) or for at least 4 h at the release site (after transport under FIL conditions; 12 experiments). The olfactory epithelia of XYL birds were locally anaesthetized a few minutes before release, while NOXYL birds were not treated with xylocain. FIL/NOFIL conditions were combined with XYL/NOXYL conditions, resulting in 4 types of experimental treatment.On average, the untreated pigeons (NOFILNOXYL) were best homeward oriented and the double-treated pigeons (FIL-XYL) poorest. More importantly, the effect of olfactory deprivation during initial flight alone (NOFIL-XYL) was small, whereas long-term filtration of environmental air was quite effective even if the pigeons could smell during release time (FIL-NOXYL) (Fig. 5).These findings indicate that pigeons usually need to be exposed to local odorous air for more than only few minutes in order to utilize information extricated from this air for site localization.Additional experiments showed that homeward orientation is also prevented, if the pigeons, although breathing natural air, are ventilated with restricted volumes of fresh air.Our results are discussed with regard to the homing mechanism of pigeons as well as to their methodological consequences.Abbreviations FIL breathing air filtered by charcoal - NOFIL breathing air unfiltered - XYL xylocain applied to pigeons' nostrils - NOXYL no xylocain applied (see p. 140)     

Monitoring airborne genotoxicants in the rubber industry using genotoxicity tests and chemical analyses

This research was designed to examine the presence of mutagenic/carcinogenic compounds in airborne pollutants in the rubber industry using an integrated chemical/biological approach. Inhalable airborne particulate matter (PM-10: <10 μm) was collected in four rubber factories using a high-volume sampler equipped with a cascade impactor for particle fractionation. The organic extracts of two different fractions (0.5–10 μm and <0.5 μm) were examined for mutagenicity with the Ames test and for in vitro DNA-damaging activity in human leukocytes by single-cell microgel electrophoresis (Comet assay). The extracts were also studied by gas chromatography/mass spectrometry (GC/MS) for polycyclic aromatic hydrocarbon (PAH) content. Nitrosamines in ambient air were sampled on cartridges and analysed by GC with a thermal energy analyser (TEA) detector. Airborne volatile genotoxins were monitored in situ using a clastogenicity plant test (Tradescantia/micronuclei test). The results showed that airborne particulates were mainly very fine (<0.5 μm) and that trace amounts of genotoxic nitrosamines (N-nitrosodimethylamine: 0.10–0.98 μg/m³; N-nitrosomorpholine: 0.77–2.40 μg/m³) and PAH (total PAH: 0.34–11.35 μg/m³) were present in air samples. Some extracts, particularly those obtained from the finest fractions, were mutagenic with the Ames test and genotoxic with the Comet assay. In situ monitoring of volatile mutagens using the Tradescantia/micronuclei test gave positive results in two working environments. The results showed the applicability of this integrated chemical–biological approach for detecting volatile and non-volatile genotoxins and for monitoring genotoxic hazards in the rubber industry.