Welfare-maximizing transmission capacity expansion under uncertainty.

We apply the JuDGE optimization package to a multistage stochastic leader-follower model that determines a transmission capacity expansion plan to maximize expected social welfare of consumers and producers who act as Cournot oligopolists in each time period. The problem is formulated as a large-scale mixed integer programme and applied to a 5-bus instance over scenario trees of varying size. The computational effort required by JuDGE is compared with solving the deterministic equivalent mixed integer programme using a state-of-the-art integer programming package. This article is part of the theme issue 'The mathematics of energy systems'.

New Insights Into the Role of Ubiquitylation of Proteins.

Posttranslational modification of proteins by the addition of ubiquitin and related modifiers has an essential role in cellular processes such as protein degradation and subcellular localization. This impacts on the study of cell and developmental biology in diseases such as cancer, and on the study of protein folding and stability in Alzheimer's disease and other diseases of protein aggregation and misfolding. Recently, there have been many additions to the ubiquitylation literature that have challenged, revised, and expanded our understanding and future directions of this process. Here we present a comprehensive overview of the classical textbook description of protein ubiquitylation and then review the recent literature that has challenged and revised the canonical models of protein ubiquitylation. We discuss the roles of noncanonical ubiquitylation at sites other than lysine residues, unconventional ubiquitylation of mixed and branched polyubiquitin chains, and highlight the role of other structural and posttranslational modifications in ubiquitylation that have been identified in the recent literature. By highlighting the assumptions that have been challenged and revised in the field of protein ubiquitylation, we hope to stimulate further study and questions about this ubiquitous protein modification.

Predictive outcomes of revision total hip replacement--a consecutive series of 1176 patients with a minimum 10-year follow-up.

The burden of revision total hip replacement (THR) surgery is increasing. With an increasing life expectancy and younger age of primary surgery this trend is set to continue. There are few data on the long-term outcome of revision THR. This retrospective study of 1176 consecutive revision THRs with a minimum 10-year follow-up from a University Teaching Hospital was undertaken to review implant survival and patient reported outcomes. Mean follow-up was 11 years with implant survival at 10 years of 82% (CI: 80-85). Implant survival varied between 58% (unexplained pain) to 84% (aseptic loosening) depending on the indication for revision surgery. Positive predictors of survival were age greater than 70 at the time of surgery (p=0.011), revision for aseptic loosening (p<0.01) and revision of both components or just the acetabular component (p<0.01). At the last review, mean Oxford Hip Score (OHS) was 34 (SD: 11.3) and 92% of the living patients with unrevised hips were satisfied with the outcome of revision surgery. This long term study has demonstrated that positive predictors of survival and outcome of revision THR surgery are age greater than 70 years, revision for aseptic loosening and component revision. This should aid surgeons in their counselling of patients prior to surgery.

Cell cycling and differentiation do not require the retinoblastoma protein during early Xenopus development.

The retinoblastoma protein (pRb) is a central regulator of the cell cycle, controlling passage through G1 phase. Moreover, pRb has also been shown to play a direct role in the differentiation of multiple tissues, including nerve and muscle. Rb null mice display embryonic lethality, although recent data have indicated that at least some of these defects are due to placental insufficiency. To investigate this further, we have examined the role of pRb in early development of the frog Xenopus laevis, which develops without the need for a placenta. Surprisingly, we see that loss of pXRb has no effect on either cell cycling or differentiation of neural or muscle tissue, while overexpression of pXRb similarly has no effects. We demonstrate that, in fact, pXRb is maintained in a hyperphosphorylated and therefore inactive state early in development. Therefore, Rb protein is not required for cell cycle control or differentiation in early embryos, indicating unusual control of these G1/G0 events at this developmental stage.

[p27Kip1 independently promotes neuronal differentiation and migration in the cerebral cortex]. / p27Kip1 independently promotes neuronal differentiation and migration in the cerebral cortex.

The generation of glutamatergic neurons by stem and progenitor cells is a complex process involving the tight coordination of multiple cellular activities, including cell cycle exit, initiation of neuronal differentiation and cell migration. The mechanisms that integrate these different events into a coherent program are not well understood. Here we show that the cyclin-dependent kinase inhibitor p27Kip1 plays an important role in neurogenesis in the mouse cerebral cortex, by promoting the differentiation and radial migration of cortical projection neurons. Importantly, p27Kip1 promotes neuronal differentiation and neuronal migration via two distinct mechanisms, which are themselves independent of the cell cycle regulatory function of p27Kip1. p27Kip1 inactivation by gene targeting or RNA interference results in neuronal differentiation and radial migration defects, demonstrating that p27Kip1 regulates cell migration in vivo. The differentiation defect, but not the migration defect, is rescued by overexpression of the proneural gene Neurogenin 2. p27Kip1 acts by stabilizing Neurogenin 2 protein, an activity carried by the N-terminal half of the protein. The migration defect resulting from p27Kp1 inactivation is rescued by blocking RhoA signalling, an activity that resides in the c-terminal half of p27Kip1. Thus, p27Kip1 plays a key role in cortical development, acting as a modular protein that independently regulates and couples multiple cellular pathways contributing to neurogenesis.

Temporal trends in major angioplasty complications: technical issues and the case for on-site coronary surgery.

The need for on-site cardiac surgery has been a component of guidelines for the practice of elective and emergency percutaneous coronary intervention (PCI). However, proportions of cases requiring emergency coronary artery bypass grafting (CABG) post-PCI have fallen. This audit of complications of PCI confirms the very low incidence of need for emergency CABG, despite increasingly complex PCI caseload. Although the availability of stents/antiplatelet pharmacotherapy probably has contributed to improved PCI outcomes, the avoidance of emergency CABG is not contingent on either extensive use of glycoprotein IIb/IIIa inhibitors or strategies of universal stenting.

Development of a regimen for rapid initiation of perhexiline therapy in acute coronary syndromes.

Perhexiline is a prophylactic anti-anginal agent that ameliorates the metabolic basis for myocardial ischaemia and is increasingly used in the management of acute coronary syndromes. No intravenous preparation is available and usual oral loading regimens require 2-3 days to achieve therapeutic drug levels. Two patients presenting to hospital with single-dose over-dosage of perhexiline (6500 mg and 1000 mg, respectively) provided a basis for examining the safety of large single dosage of perhexiline and associated time-course of drug levels. Neither patient had previously taken perhexiline. Peak plasma perhexiline concentrations occurred within 12 h of ingestion and were 2.58 and 0.50 mg/L, respectively (therapeutic range 0.15-0.60 mg/L). The first patient developed transient nausea and vomiting; the second patient had no adverse effects. Subsequently, a series of 10 patients with acute coronary syndromes received an 800-mg loading dose. Peak concentrations occurred within 12 h postdose; the mean levels achieved were 0.40 +/- 0.16 mg/L (standard error of the mean). No serious adverse effects were seen. Two patients reported transient nausea or vomiting within 24 h of the loading dose. The utility of this rapid loading regimen for incremental suppression of myocardial ischaemia remains to be assessed.

Cell cycle and cell fate in the nervous system.

Recently, a number of molecules originally thought to have a primary role in cell determination have been shown to affect the cell cycle at specific check points, while other molecules discovered for their roles in the cell cycle progression are known to affect the determination and differentiation of neurons. These discoveries have led to a more detailed investigation of the complex molecular machinery that co-ordinates proliferation and differentiation.

Inhibiting mutations in the transforming growth factor beta type 2 receptor in recurrent human breast cancer.

Members of the transforming growth factor beta (TGF-beta) family are potent inhibitors of the growth of many epithelial cell types. Transmembrane signaling by TGF-beta occurs via a complex of the serine/threonine kinases TGF-beta type 1 receptor and TGF-beta type 2 receptor (TGFBR2), and inactivating mutations in the latter have recently been detected in some primary tumors and in several types of tumor-derived cell lines. The most common mutations that have been identified in TGFBR2 are frameshifts in a repetitive polyadenine region in replication error-positive colorectal carcinomas that result in a truncated protein and absence of receptor expression at the cell surface. A number of point mutations in the highly conserved serine/threonine kinase domain of TGFBR2 have also been reported, some of which have been correlated with either loss of trans-phosphorylation of TGF-beta type 1 receptor or constitutive activation of trans-phosphorylation. No TGFBR2 mutations have been reported in human breast tumors, but anomalous expression of TGF-beta in breast carcinomas suggests that TGF-beta signaling may be defective. We have therefore systematically examined unmatched sets of 17 primary and 17 recurrent breast tumor samples for mutations in TGFBR2, restricted to those regions of the gene in which mutations have previously been reported. None of the previously reported mutations was detected, but four novel mutations (V387M, N435S, V447A, and L452M) were found in the kinase domain in recurrent tumors. No mutations were detected in primary tumors. TGF-beta signaling was significantly inhibited by each of the N435S, V447A, and L452M mutations.

Nuclear chaperones.

We discuss nuclear chaperones that bind correctly folded protein subunits and mediate molecular interactions, particularly between proteins and nucleic acids. The charge of these chaperones helps to prevent non-specific electrostatic interactions between the components. Thus, an ordered assembly of macromolecular complexes is mediated, most notably in the formation and maintenance of chromatin, though similar principles are likely to apply in ribonucleoprotein assembly. Here, we discuss roles for nuclear chaperones in mediating nucleosome assembly and remodelling during DNA replication and transcription, and upon fertilisation.

p27Xic1, a Cdk inhibitor, promotes the determination of glial cells in Xenopus retina.

p27Xic1, a member of the Cip/Kip family of Cdk inhibitors, besides its known function of inhibiting cell division, induces Müller glia from retinoblasts. This novel gliogenic function of p27Xic1 is mediated by part of the N-terminal domain near but distinct from the region that inhibits cyclin-dependent kinases. Cotransfections with dominant-negative and constitutively active Delta and Notch constructs indicate that the gliogenic effects of p27Xic1 work within the context of an active Notch pathway. The gradual increase of p27Xic1 in the developing retina thus not only limits the number of retinal cells but also increasingly favors the fate of the last cell type to be born in the retina, the Müller glia.

Comparison of the effects of diazepam on the fear-potentiated startle reflex and the fear-inhibited light reflex in man.

It has been shown previously that the amplitude of the acoustic startle reflex is enhanced, and the amplitude of the light reflex reduced, when subjects anticipate an aversive event, compared to periods when subjects are resting ('fear-potentiated startle reflex' and 'fear-inhibited light reflex'). We examined whether the anxiolytic diazepam would reverse the effects of threat on the startle and pupillary reflexes. Twelve male volunteers participated in three weekly sessions in which they received oral treatment with placebo, diazepam 5 mg and diazepam 10 mg, according to a balanced crossover double-blind design. One hour after ingestion of the treatments, miotic responses to light pulses and electromyographic responses of the orbicularis oculi muscle to sound pulses were elicited during alternating periods in which the threat of an electric shock (electrodes attached to the subject's wrist) was present (THREAT) and absent (SAFE). The THREAT condition was associated with a significant increase in the amplitude of the electromyographic (EMG) response, a significant reduction of the miotic response amplitude, and an increase in self-rated anxiety. Diazepam attenuated all these effects of THREAT. Diazepam did not affect the amplitude of the miotic response under the SAFE condition, but did suppress the EMG response under this condition. These results confirm the validity of the fear-potentiated startle reflex and fear-inhibited light reflex as laboratory models of human anxiety, and reveal some differences between the effects of diazepam on the two reflexes.

Giant eyes in Xenopus laevis by overexpression of XOptx2.

Overexpression of XOptx2, a homeodomain-containing transcription factor expressed in the Xenopus embryonic eye field, results in a dramatic increase in eye size. An XOptx2-Engrailed repressor gives a similar phenotype, while an XOptx2-VP16 activator reduces eye size. XOptx2 stimulates bromodeoxyuridine incorporation, and XOptx2-induced eye enlargement is dependent on cellular proliferation. Moreover, retinoblasts transfected with XOptx2 produce clones of cells approximately twice as large as control clones. Pax6, which does not increase eye size alone, acts synergistically with XOptx2. Our results suggest that XOptx2, in combination with other genes expressed in the eye field, is crucially involved in the proliferative state of retinoblasts and thereby the size of the eye.

Neuronal differentiation and patterning in Xenopus: the role of cdk5 and a novel activator xp35.2.

Cdk5, a member of the cyclin-dependent kinase family, has been shown to play an important role in development of the central nervous system in mammals when partnered by its activator p35. Here we describe the cloning and characterization of a novel activator of cdk5 in Xenopus, Xp35.2. Xp35.2 is expressed during development initially in the earliest differentiating primary neurons in the neural plate and then later in differentiating neural tissue of the brain. This is in contrast to the previously described Xenopus cdk5 activator Xp35.1 which is expressed over the entire expanse of the neural plate in both proliferating and differentiating cells. Expression of both Xp35.1 and Xp35.2 and activation of cdk5 kinase occur when terminal neural differentiation is induced by neurogenin and neuro D overexpression but not when only early stages of neural differentiation are induced by noggin. Moreover, blocking cdk5 kinase activity specifically results in disruption and reduction of the embryonic eye where cdk5 and its Xp35 activators are expressed. Thus, cdk5/p35 complexes function in aspects of neural differentiation and patterning in the early embryo and particularly in formation of the eye.

The role of cyclin-dependent kinase 5 and a novel regulatory subunit in regulating muscle differentiation and patterning.

Cyclin-dependent kinase 5, coupled with its activator p35, is required for normal neuronal differentiation and patterning. We have isolated a novel member of the p35 family, Xp35.1, from Xenopus embryos which can activate cdk5. Xp35.1 is expressed in both proliferating and differentiated neural and mesodermal cells and is particularly high in developing somites where cdk5 is also expressed. Using dominant-negative cdk5 (cdk5 DN), we show that cdk5 kinase activity is required for normal somitic muscle development; expression of cdk5 DN results in disruption of somitic muscle patterning, accompanied by stunting of the embryos. Using explants of animal pole tissue from blastula embryos, which will differentiate into mesoderm in response to activin, we show that blocking cdk5 kinase activity down-regulates the expression of the muscle marker muscle actin in response to activin, whereas the pan-mesodermal marker Xbra is unaffected. Expression of MyoD and MRF4 (master regulators of myogenesis) is suppressed in the presence of cdk5 DN, indicating that these myogenic genes may be a target for cdk5 regulation, whereas the related factor Myf5 is largely unaffected. In addition, overexpression of Xp35.1 disrupts muscle organization. Thus, we have demonstrated a novel role for cdk5 in regulating myogenesis in the early embryo.

Molecular and cellular characterization of CRP1, a Drosophila chromatin decondensation protein.

CRP1, a Drosophila nuclear protein that can catalyze decondensation of demembranated Xenopus sperm chromatin was cloned and its primary structure was deduced from cDNA sequence. Alignment of deduced amino acid sequence with published sequences of other proteins revealed strong homologies to Xenopus nucleoplasmin and NO38. CRP1 is encoded by one or several closely related genes found at a single locus, position 99A on the right arm of chromosome 3. CRP1 mRNA is expressed throughout Drosophila development; it is highest during oogenesis and early embryogenesis. mRNA levels correlate closely with levels of protein expression measured previously. Results of chemical crosslinking indicate that CRP1 is either tetrameric or pentameric; similar ambiguity was revealed by direct visualization using scanning transmission electron microscopy. Consistent with previously published results, parallel crosslinking studies of Xenopus nucleoplasmin suggested a pentameric structure. Scanning transmission electron microscopic examination after negative staining revealed that CRP1 and Xenopus nucleoplasmin are morphologically similar. CRP1 is able to substitute for nucleoplasmin in Xenopus egg extract-mediated sperm chromatin decondensation. In vitro, CRP1-induced decondensation is accompanied by direct binding of CRP1 to chromatin.

Hyperphosphorylation of nucleoplasmin facilitates Xenopus sperm decondensation at fertilization.

Previous studies showed that the nuclear phosphoprotein nucleoplasmin performs the first stage of chromatin decondensation of Xenopus sperm at fertilization. It binds and removes sperm basic proteins replacing them with histones. We now show that this activity depends upon the massive hyperphosphorylation of nucleoplasmin that occurs when oocytes mature into eggs. Egg extracts or purified hyperphosphorylated egg nucleoplasmin decondense sperm chromatin and remove sperm basic proteins much faster than oocyte extracts or hypophosphorylated oocyte nucleoplasmin. Furthermore, dephosphorylation of egg nucleoplasmin slows sperm decondensation and prevents basic protein removal from sperm chromatin. We conclude that hyperphosphorylation of nucleoplasmin is used to modulate the rapid changes in chromatin structure that accompany early development in Xenopus.

E2F and its developmental regulation in Xenopus laevis.

The transcription factor E2F has been implicated in cell cycle control by virtue of its association with cyclins, cyclin-dependent kinases, and pRb-related tumor suppressor gene products. Eggs and embryos from the frog Xenopus laevis have been used to investigate the characteristics of E2F-like molecules in the Xenopus cell cycle and throughout early development. We find multiple E2F species in Xenopus eggs, at least one of which is modified by phosphorylation. The vast majority of E2F remains in the free form throughout the very early embryonic cell cycle, and it also remains predominantly free until some time after the mid-blastula transition, the onset of zygotic transcription. At this time, E2F complexes significantly to pRb but not to cdk2, although cdk2 binding is found in tissue culture cells from a very advanced stage in embryogenesis. This suggests that the complexing of E2F to cyclins, cyclin-dependent kinases, and tumor suppressor gene products may be controlled separately in early Xenopus development. Thus, the association of E2F with other molecules may not result solely from processes affecting cell cycle progression but may also reflect developmental and differentiation cues.

Chromatin decondensation in Drosophila embryo extracts.

Decondensation of sperm chromatin in cell-free Drosophila embryo extracts was efficient, rapid, and synchronous. The decondensation activity was N-ethylmaleimide-resistant, soluble, and heat-stable. Two specific proteins, X and Y, were removed selectively from Xenopus sperm coincident with morphological decondensation. A heat-stable protein, p22, was purified to apparent homogeneity from Drosophila melanogaster embryos by a procedure optimized for the purification of Xenopus laevis nucleoplasmin. Although itself capable of catalyzing decondensation of Xenopus sperm, the precise relationship of Drosophila p22 to Xenopus nucleoplasmin is unclear. Drosophila p22 and Xenopus nucleoplasmin were immunologically distinct. Moreover, p22 was present as a nuclear protein throughout Drosophila development as determined both by immunoblot and by indirect immunofluorescence analyses. Drosophila embryo extracts largely or completely immunodepleted of p22 lost some but not all heat-stable decondensation activity. These observations lead to the conclusion that Drosophila embryo extracts contain at least two heat-stable sperm decondensation factors.