Deletion of the XIST promoter from the human inactive X chromosome compromises polycomb heterochromatin maintenance.

Silencing most gene expression from all but one X chromosome in female mammals provides a means to overcome X-linked gene expression imbalances with males. Central to establishing gene silencing on the inactivated X chromosome are the actions of the long non-coding RNA XIST that triggers the repackaging of the chosen X into facultative heterochromatin. While understanding the mechanisms through which XIST expression is regulated and mediates its affects has been a major focus of research since its discovery, less is known about the role XIST plays in maintaining chromatin at the human inactive X chromosome (Xi). Here, we use genome engineering to delete the promoter of XIST to knockout expression from the Xi in non-cancerous diploid human somatic cells. Although some heterochromatin features exhibit limited change at the Xi, two of those assessed showed significant reductions including histone H2A monoubiquitylation at lysine 119 and histone H3 trimethylation at lysine 27, both of which are covalent histone modifications catalyzed by the polycomb repressive complexes 1 and 2 respectively. Coupled with these reductions, we observed an occasional gain of euchromatin signatures on Xp, but despite these signs of chromatin instability, we did not observe appreciable changes in the reactivation of genes from the Xi. Collectively, these data are consistent with maintenance of dosage compensation at the Xi involving multiple redundant layers of gene silencing.

Total intravenous anesthesia with propofol and S(+)-ketamine in rabbits.

OBJECTIVE: To evaluate total intravenous anesthesia with propofol alone or in combination with S(+)-ketamine in rabbits undergoing surgery. STUDY DESIGN: Prospective, randomized, blinded trial. ANIMALS: Nine 6-month-old New Zealand white rabbits, weighing 2.5-3 kg. METHODS: Animals received acepromazine (0.1 mg kg(-1)) and buprenorphine (20 microg kg(-1)) IM, and anesthesia was induced with propofol (2 mg kg(-1)) and S(+)-ketamine (1 mg kg(-1)) IV. Rabbits received two of three treatments: propofol (0.8 mg kg(-1) minute(-1)) (control treatment, P), propofol (0.8 mg kg(-1) minute(-1)) + S(+)-ketamine (100 microg kg(-1) minute(-1)) (PK100) or propofol (0.8 mg kg(-1) minute(-1)) + S(+)-ketamine (200 microg kg(-1) minute(-1)) (PK200). All animals received 100% O(2) during anesthesia. Heart rate, mean arterial pressure, hemoglobin oxygen saturation and respiratory rate were measured every 5 minutes for 60 minutes. Blood-gas parameters were measured at zero time and 60 minutes. Additional propofol injections, if necessary, and recovery time were recorded. RESULTS: An increase in heart rate was observed in P and PK200 up to 10 minutes after induction of anesthesia. Blood pressure decreased from baseline values during the first 10 minutes in P and PK200, and during the first 15 minutes and between 45 and 55 minutes in PK100. A reduction in respiratory rate was observed after 5 minutes in all treatments. Respiratory acidosis was observed in all treatments. Six (2.8) [median (interquartile range)] further propofol injections were necessary in P, which differed statistically from PK100 [1 (0.2)] and PK200 [2 (0.6)]. Recovery time was shorter in P compared with PK100 and PK200, being [7.5 minutes (4.11)], [17.5 minutes (10.30)], and [12 minutes (10.30)], respectively. CONCLUSIONS AND CLINICAL RELEVANCE: S(+)-ketamine potentiates propofol-induced anesthesia in rabbits, providing better maintenance of heart rate. All of these techniques were accompanied by clinically significant respiratory depression.