Fine-tune of intrinsic ERK activity by extrinsic BMP signaling in mouse embryonic stem cells

Embryonic stem (ES) cells hold great promise in regenerative medicine and it is an urgent task to understand the underlying molecular mechanisms that control ES cell fate choice between self-renewal and differentiation. In mouse ES cells, extrinsic leukemia inhibitory factor (LIF) and bone morphogenetic protein (BMP) signaling pathways play pivotal roles in maintaining the self-renewal status under serum and feeder free culture conditions. Intrinsic extracellular-signal regulated kinase (ERK) activity is also important in determining mouse ES cell fate-low ERK activity keeps mouse ES cell self-renewal while high ERK activity drives differentiation. We recently found that while LIF signaling augments ERK activity, BMP signaling inhibits ERK activity in mouse ES cells via direct upregulation of an ERK phosphatase-dual-specificity phosphatase 9. The cooperative effects of LIF and BMP signaling keep appropriate ERK activity and maintain mouse ES cell self-renewal (Li et al., 2012). These findings shed light on how extrinsic signals converge to intrinsic signaling molecules to regulate cell fate determination. This perspective summarizes our recent new findings and discusses the current unsolved questions and future directions.

Percutaneous hollow screws for treatment of the vertical sacrum longitudinal fracture / 中国骨伤

<p><b>OBJECTIVE</b>To introduce percutaneous hollow screws for treatment of the vertical sacrum longitudinal fracture and evaluate the preliminary therapeutic outcomes.</p><p><b>METHODS</b>From January 1999 to December 2006, 24 cases with vertical sacrum longitudinal fractures inchuded 15 males and 9 females were treated by percutaneous hollow screws, with an average age of 35 years ranging from 18 to 61 years. Accordng to Denis'classification of sacral fracture, there were 6 cases of type I, 11 of type 1 and 7 of type II.</p><p><b>RESULTS</b>The operation lasted for 30 to 65 minutes (averaged 48 minutes). All of them were followed up for 3 to 36 months (averaged 18.6 months). According to improved effective standard of pelvic trauma, the result of radiography was excellent in 18 cases, good in 5 and poor in 1, and the clinical evaluation was exellent in 16, good in 8.</p><p><b>CONCLUSION</b>Treatment of the vertical sacrum longitudinal fracture with percutaneous hollow screws is a comparatively reliable method and has the advantages of more precise with few postoperative complications and allows the patient early mobilization.</p>