Restricting Dosage Compensation Complex Binding to the X Chromosomes by H2A.Z/HTZ-1

Dosage compensation ensures similar levels of X-linked gene products in males (XY or XO) and females (XX), despite their different numbers of X chromosomes. In mammals, flies, and worms, dosage compensation is mediated by a specialized machinery that localizes to one or both of the X chromosomes in one sex resulting in a change in gene expression from the affected X chromosome(s). In mammals and flies, dosage compensation is associated with specific histone posttranslational modifications and replacement with variant histones. Until now, no specific histone modifications or histone variants have been implicated in Caenorhabditis elegans dosage compensation. Taking a candidate approach, we have looked at specific histone modifications and variants on the C. elegans dosage compensated X chromosomes. Using RNAi-based assays, we show that reducing levels of the histone H2A variant, H2A.Z (HTZ-1 in C. elegans), leads to partial disruption of dosage compensation. By immunofluorescence, we have observed that HTZ-1 is under-represented on the dosage compensated X chromosomes, but not on the non-dosage compensated male X chromosome. We find that reduction of HTZ-1 levels by RNA interference (RNAi) and mutation results in only a very modest change in dosage compensation complex protein levels. However, in these animals, the X chromosome–specific localization of the complex is partially disrupted, with some nuclei displaying DCC localization beyond the X chromosome territory. We propose a model in which HTZ-1, directly or indirectly, serves to restrict the dosage compensation complex to the X chromosome by acting as or regulating the activity of an autosomal repellant

Stabilised suspending efficiency of Laponite XLG and sodium carboxy methylcellulose blend in the formulation of sulphamerazine suspension

Charged drugs like Sulphamerazine may make pseudoplastic/plastic materials become Newtonian and loose their suspending power. In this study, laponite XLG (laponite), a synthetic hectorite was employed as a protective colloid and viscosity stabilizer in a blend with sodium carboxymethylcellulose (SCMC), which exhibits high viscosity at low rates of shear and shear thinning characteristics. The viscosities and yield values of suitable concentrations (2%w/w SCMC, 4%w/w laponite, and a 1:1 ratio of 2%w/w laponite – SCMC blend) that yielded pseudoplastic/plastic properties were studied in the absence and presence of 1 - 4%w/w sulphamerazine. For this purpose, the rheograms of the systems were obtained by the use of a Haake rotoviscometer RV 12 utilizing a cup and rotor sensor system MV 1. In the absence of sulpamerazine, the blend had higher viscosity and yield value than either material alone, which were resistant to change in the presence of sulphamerazine. The blend was consequently very efficient in suspending sulphamerazine powder with no separation. Laponite changed from a pseudoplastic to a Newtonian fluid in the presence of sulphamerazine, but gave a flocculated suspension with a clear supernatant and a large sedimentation volume that was readily redispersed. SCMC on the other hand, allowed the sedimentation of sulphamerazine with low sedimentation volume and misty supernatant. The sediment was also difficult to redisperse, suggesting a deflocculated system. Laponite – SCMC blend could be a very useful and efficient suspending agent in the liquid formulation of difficult insoluble drugs, including magnesium trisilicate whose many marketed forms often show separation. Key words: Laponite XLG,sodium; Carboxymethylcellulose and their blend; Suspending efficienc; Sulphamerazine suspension. Nig. J. Pharm. Res. 3(1) 2004: 56-6

Controls on Water Levels and Salinity In a Barrier Island Mangrove, Indian River Lagoon, Florida

We examined controls on water levels and salinity in a mangrove on a carbonate barrier island along the Indian River Lagoon, east-central Florida. Piezometers were installed at 19 sites throughout the area. Groundwater was sampled at 17 of these sites seasonally for three years. Head measurements were taken at the other two sites at 15-minute intervals for one year. Water levels in the mangrove are almost always lower than lagoon water levels. Spectral analysis of water levels showed that mangrove groundwater levels are not tidally influenced. Salinities vary spatially, with values of ∼10 psu in uplands, ∼30 psu in regularly-flushed mangroves, and ∼75 psu in irregularly-flushed mangroves. Cation and anion concentrations and stable isotope compositions indicate that water salinities are largely controlled by enrichment due to evapotranspiration. A shore-perpendicular electrical resistivity survey showed that the freshwater lens is restricted to uplands and that hypersaline waters extend deeply below the mangrove. These results indicate that evapotranspiration lowers water levels in the mangrove, which causes Indian River Lagoon water to flow into the mangrove where it evapoconcentrates and descends, forming a thick layer of high-salinity water below the mangrove