These studies address whether XIST RNA is properly localized to the X chromosome in somatic cells where human XIST expression is reactivated, but fails to result in X inactivation (Tinker, A.V., and C.J. Brown. 1998. Nucl. Acids Res. 26:2935-2940). Despite a nuclear RNA accumulation of normal abundance and stability, XIST RNA does not localize in reactivants or in naturally inactive human X chr...

In the early mammalian embryo, X chromosome inactivation (XCI) achieves dosage parity between males and females for X-linked genes. During mouse development, imprinted paternal XCI is observed first and switches to random XCI in the epiblast but not placental lineages. The mechanism by which this epigenetic switch occurs is currently unknown. Here, we establish an ex vivo model for imprinting a...

X chromosome inactivation (XCI) is initiated by expression of the noncoding Xist RNA in the female embryo. Tsix, the antisense noncoding partner of Xist, serves as its regulator during both imprinted and random XCI. Here, we show that Tsix in part acts through a 34mer repeat, DXPas34. DXPas34 contains bidirectional promoter activity, producing overlapping forward and reverse transcripts. We gen...

Population-genetic models are developed to investigate the consequences of viability selection at a diallelic X-linked locus subject to genomic imprinting. Under complete paternal-X inactivation, a stable polymorphism is possible under the same conditions as for paternal-autosome inactivation with differential selection on males and females. A necessary but not sufficient condition is that ther...

X inactivation--the transcriptional silencing of one X chromosome copy per female somatic cell--is universal among therian mammals, yet the choice of which X to silence exhibits considerable variation among species. X inactivation strategies can range from strict paternally inherited X inactivation (PXI), which renders females haploid for all maternally inherited alleles, to unbiased random X i...

Xist (X-inactive specific transcript) plays a crucial role in X-inactivation. This non-coding RNA becomes upregulated on the X chromosome that is to be inactivated upon differentiation. Previous studies have revealed that although maintenance-type DNA methylation is not essential for X-inactivation to occur, it is required for the stable repression of Xist in differentiated cells. However, it i...

X chromosome inactivation (XCI) is an epigenetic mechanism that silences the majority of genes on one X chromosome in females. Previous studies have suggested that the spread of XCI might be facilitated in part by common repeats such as long interspersed nuclear elements (LINEs). However, owing to the unusual sequence content of the X and the nonrandom distribution of genes that escape XCI, it ...

Inactivation kinetics of poliovirus type 1 in ozone demand-free water was investigated by utilizing a fast-flow mixing apparatus. Ozonated water and a solution of ozone demand-free water containing a known quantity of poliovirus type 1 were introduced simultaneously into a mixing chamber, both at a constant rate. This mixture was then passed through a narrow tube of known length and diameter in...

X-chromosome inactivation is widely believed to be random in early female development and to result in a mosaic distribution of cells, approximately half with the paternally derived X chromosome inactive and half with the maternally derived X chromosome inactive. Significant departures from such a random pattern are hallmarks of a variety of clinical states, including being carriers for severe ...

Adenovirus is a focus of the water treatment community because of its resistance to standard, monochromatic low-pressure (LP) UV irradiation. Recent research has shown that polychromatic, medium-pressure (MP) UV sources are more effective than LP UV for disinfection of adenovirus when viral inactivation is measured using cell culture infectivity assays; however, UV-induced DNA damage may be rep...