A cis-acting control region is required exclusively for the tissue-specific imprinting of Gnas.

Genomic imprinting brings about allele-specific silencing according to parental origin. Silencing is controlled by cis-acting regulatory regions that are differentially marked during gametogenesis and can act over hundreds of kilobases to silence many genes. Two candidate imprinting control regions (ICRs) have been identified at the compact imprinted Gnas cluster on distal mouse chromosome 2, one at exon 1A upstream of Gnas itself and one covering the promoters for Gnasxl and the antisense Nespas (ref. 8). This imprinted cluster is complex, containing biallelic, maternally and paternally expressed transcripts that share exons. Gnas itself is mainly biallelically expressed but is weakly paternally repressed in specific tissues. Here we show that a paternally derived targeted deletion of the germline differentially methylated region at exon 1A abolishes tissue-specific imprinting of Gnas. This rescues the abnormal phenotype of mice with a maternally derived Gnas mutation. Imprinting of alternative transcripts, Nesp, Gnasxl and Nespas (ref. 13), in the cluster is unaffected. The results establish that the differentially methylated region at exon 1A contains an imprinting control element that specifically regulates Gnas and comprises a characterized ICR for a gene that is only weakly imprinted in a minority of tissues. There must be a second ICR regulating the alternative transcripts.

Non-random distribution of instability-associated chromosomal rearrangement breakpoints in human lymphoblastoid cells.

Genomic instability is observed in tumors and in a large fraction of the progeny surviving irradiation. One of the best-characterized phenotypic manifestations of genomic instability is delayed chromosome aberrations. Our working hypothesis for the current study was that if genomic instability is in part attributable to cis mechanisms, we should observe a non-random distribution of chromosomes or sites involved in instability-associated rearrangements, regardless of radiation quality, dose, or trans factor expression. We report here the karyotypic examination of 296 instability-associated chromosomal rearrangement breaksites (IACRB) from 118 unstable TK6 human B lymphoblast, and isogenic derivative, clones. When we tested whether IACRB were distributed across the chromosomes based on target size, a significant non-random distribution was evident (p<0.00001), and three IACRB hotspots (chromosomes 11, 12, and 22) and one IACRB coldspot (chromosome 2) were identified. Statistical analysis at the chromosomal band-level identified four IACRB hotspots accounting for 20% of all instability-associated breaks, two of which account for over 14% of all IACRB. Further, analysis of independent clones provided evidence within 14 individual clones of IACRB clustering at the chromosomal band level, suggesting a predisposition for further breaks after an initial break at some chromosomal bands. All of these events, independently, or when taken together, were highly unlikely to have occurred by chance (p<0.000001). These IACRB band-level cluster hotspots were observed independent of radiation quality, dose, or cellular p53 status. The non-random distribution of instability-associated chromosomal rearrangements described here significantly differs from the distribution that was observed in a first-division post-irradiation metaphase analysis (p=0.0004). Taken together, these results suggest that genomic instability may be in part driven by chromosomal cis mechanisms.

Intraoperative monitoring during vascular surgery.

The principal objectives of intraoperative monitoring are to improve perioperative outcome, facilitate surgery and reduce adverse events, using continuously collected data of cardiopulmonary,neurologic and metabolic function to guide pharmacologic and physiologic therapy. Although sophisticated and reliable apparatus may be used to collect these data they are useless, or even harmful, without proper interpretation. This article provides a comprehensive overview of recent publications on the history,philosophy, and semantics of monitoring.