Saltatory remodeling of Hox chromatin in response to rostrocaudal patterning signals

Hox genes controlling motor neuron subtype identity are expressed in rostrocaudal patterns that are spatially and temporally collinear with their chromosomal organization. Here we demonstrate that Hox chromatin is subdivided into discrete domains that are controlled by rostrocaudal patterning signals that trigger rapid, domain-wide clearance of repressive histone H3 Lys27 trimethylation (H3K27me3) polycomb modifications. Treatment of differentiating mouse neural progenitors with retinoic acid leads to activation and binding of retinoic acid receptors (RARs) to the Hox1–Hox5 chromatin domains, which is followed by a rapid domain-wide removal of H3K27me3 and acquisition of cervical spinal identity. Wnt and fibroblast growth factor (FGF) signals induce expression of the Cdx2 transcription factor that binds and clears H3K27me3 from the Hox1–Hox9 chromatin domains, leading to specification of brachial or thoracic spinal identity. We propose that rapid clearance of repressive modifications in response to transient patterning signals encodes global rostrocaudal neural identity and that maintenance of these chromatin domains ensures the transmission of positional identity to postmitotic motor neurons later in development.Leona M. and Harry B. Helmsley Charitable TrustNational Institutes of Health (U.S.) (Grant P01 NS055923)Smith Family Foundatio

Organic analysis for urban geochemical survey soil samples

Summary This chapter contains sections titled: Introduction Field sample preservation Organic sample preparation Instrumental analysis for organic analytes Application of quality assurance/quality control Reference

Chemicals in the environment : implications for global sustainability

The impact of chemicals on the environment and human health is a cause of increasing concern. Although many studies continue to be carried out on this subject, most address only individual chemicals or particular groups of chemicals, such as metals or radioactive substances. In this paper, we consider the availability of data and knowledge about potentially harmful chemicals from the national to international scale and suggest a strategy to help prevent chemical pollution or deficiencies damaging global sustainability into the 21st century. The main groups of chemicals considered are: (i) Potentially harmful inorganic elements such as As, Cd, Hg and Pb known to have adverse physiological effects at low levels, and elements and species such as Se, I and NOx that can be essential or harmful depending on their concentration, speciation and bioavailability. Chemical elements such as Ga, In and the PGEs that are increasingly used in the development of new materials, including nanotechnology applications, are also discussed briefly. (ii) Radioactive substances, including naturally occurring radioisotopes, such as 238U and its decay products 226Ra and 222Rn, and processed materials, such as depleted uranium (DU), which affect the environment and human health because of their radiological and chemical toxicity. Data on isotopes from the nuclear industry, such as the relatively short-lived isotopes 137Cs and 90Sr, are also discussed, including from accidental releases such as Chernobyl in 1986. Isotopes with longer half-lives such as 243Am and 240Pu, which are important in the development of nuclear waste management strategies are also considered. (iii) Persistent organic pollutants (POPs) including many synthetic chemicals such as dichlorodiphenyltrichloroethane (DDT), polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs), flame retardants and their metabolites, which are characterised by their persistence, bioaccumulation (lipophilicity) and toxicity (PBT) properties. Other synthetic chemicals such as perfluorooctane sulphonate (PFOS), which have different bioaccumulation properties, are considered briefly. (iv) Human and veterinary pharmaceuticals, of which there is increasing evidence of their presence in the environment. These substances are of particular concern because many are designed to target specific biological receptors and hence can have potentially deleterious effects at exceptionally low concentrations. All these groups of chemicals include endocrine disrupting chemicals (EDCs), capable of disrupting animal and human hormone systems (including sex and thyroid). Geochemical databases such as those prepared by the Forum of European Geological Surveys (FOREGS) and the British Geological Survey (BGS) provide systematic information on levels of inorganic chemicals in the environment. Similarly, airborne radiometric databases provide systematic information on the distribution of radioactive substances. Examples of such data are used to demonstrate how the distribution of chemicals in the environment can be mapped, and how modelling and monitoring systems derived from them are of strategic importance in understanding the impact of chemicals on ecosystems and human health from the national to global scale. There is concern, however, about the lack of such systematic data for organic chemicals. It is argued that such systematic data for all chemicals is crucial for sustaining the Earth's life-support systems into the 21st century

Sample preparation and inorganic analysis for urban geochemical survey soil and sediment samples

Summary This chapter contains sections titled: Introduction Field sample preservation Physical sample preparation Determination of bulk properties Analytical sample preparation Instrumental analysis for inorganic analytes Application of quality assurance Health and safety issues Reference