Application of the ideas and techniques of classical fluid mechanics to some problems in physical oceanography.

This review makes a case for describing many of the flows observed in our oceans, simply based on the Euler equation, with (piecewise) constant density and with suitable boundary conditions. The analyses start from the Euler and mass conservation equations, expressed in a rotating, spherical coordinate system (but the f-plane and ß-plane approximations are also mentioned); five examples are discussed. For three of them, a suitable non-dimensionalization is introduced, and a single small parameter is identified in each case. These three examples lead straightforwardly and directly to new results for: waves on the Pacific Equatorial Undercurrent (EUC) with a thermocline (in the f-plane); a nonlinear, three-dimensional model for EUC-type flows (in the ß-plane); and a detailed model for large gyres. The other two examples are exact solutions of the complete system: a flow which corresponds to the underlying structure of the Pacific EUC; and a flow based on the necessary requirement to use a non-conservative body force, which produces the type of flow observed in the Antarctic Circumpolar Current. (All these examples have been discussed in detail in the references cited.) This review concludes with a few comments on how these solutions can be extended and expanded.This article is part of the theme issue 'Nonlinear water waves'.

The Perception of Threat from Emotions in Predicting Binge Eating Behaviours in People Who Are Obese and Seeking Treatment for Their Weight.

OBJECTIVE: The affect regulation theory suggests that people binge eat to regulate negative emotional states. In this study, we used a basic emotions perspective to consider the role of perceived threat of emotions, emotional suppression and reduced emotional expressiveness in predicting binge eating behaviours in people who are obese. METHOD: Treatment-seeking participants with obesity (N = 51, body mass index range from 30.8 to 60.2 kg m-2 ) completed measures of 'perception of threat from emotion' as well as 'emotional expressiveness' and binge eating. RESULTS: The results demonstrated that perceived threat of sadness predicted binge eating (ß = .55, p < .05). Additionally, a mediation analysis revealed that reduced emotional expressiveness mediated the relationship between perceived threat of fear and binge eating (ß = .25, 95%). DISCUSSION: These findings are contextualized within a theoretical perspective that suggests that individuals who binge eat are threatened by certain emotional states and they use binge eating to suppress certain, but not all, emotional states. Copyright © 2015 John Wiley & Sons, Ltd. KEY PRACTITIONER MESSAGE: Considering basic emotions within binge eating should be a part of a psychological assessment and treatment. This should consider how emotions could often be perceived as being threatening and their expression is limited. It is possible that the emotions of fear and sadness appear to be particularly threatening within binge eating/obese populations.

Negative regulation of HIF in skeletal muscle of elite endurance athletes: a tentative mechanism promoting oxidative metabolism.

The transcription factor hypoxia-inducible factor (HIF) has been suggested as a candidate for mediating training adaptation in skeletal muscle. However, recent evidence rather associates HIF attenuation with a trained phenotype. For example, a muscle-specific HIF deletion increases endurance performance, partly through decreased levels of pyruvate dehydrogenase kinase 1 (PDK-1). HIF activity is regulated on multiple levels: modulation of protein stability, transactivation capacity, and target gene availability. Prolyl hydroxylases (PHD1-3) induces HIF degradation, whereas factor-inhibiting HIF (FIH) and the histone deacetylase sirtuin-6 (SIRT6) repress its transcriptional activity. Together, these negative regulators introduce a mechanism for moderating HIF activity in vivo. We hypothesized that long-term training induces their expression. Negative regulators of HIF were explored by comparing skeletal muscle tissue from moderately active individuals (MA) with elite athletes (EA). In elite athletes, expression of the negative regulators PHD2 (MA 73.54 ± 9.54, EA 98.03 ± 6.58), FIH (MA 4.31 ± 0.25, EA 30.96 ± 7.99) and SIRT6 (MA 0.24 ± 0.07, EA 11.42 ± 2.22) were all significantly higher, whereas the response gene, PDK-1 was lower (MA 0.12 ± 0.03, EA 0.04 ± 0.01). Similar results were observed in a separate 6-wk training study. In vitro, activation of HIF in human primary muscle cell culture by PHD inactivation strongly induced PDK-1 (0.84 ± 0.12 vs 4.70 ± 0.63), providing evidence of a regulatory link between PHD activity and PDK-1 levels in a relevant model system. Citrate synthase activity, closely associated with aerobic exercise adaptation, increased upon PDK-1 silencing. We suggest that training-induced negative regulation of HIF mediates the attenuation of PDK-1 and contributes to skeletal muscle adaptation to exercise.

Atmospheric undular bores.

We show that a recently-derived model for the propagation of nonlinear waves in the atmosphere admits undular bores as travelling-wave solutions. These solutions represent waves consisting of a damped oscillation behind a front that is preceded by a uniform breeze-type flow. The generation of such wave profiles requires a jump in the heat source across the leading front of the wave, a feature that is consistent with observations.

Tumour oxygenation: implications for breast cancer prognosis.

There are areas of limited oxygen availability in most solid tumours, including breast cancer. Hypoxia in solid tumours is mainly a consequence of poor perfusion. Structural and functional abnormalities of newly formed tumour vessels cause spatial and temporal heterogeneity of tissue perfusion. The two principal mediators of hypoxia response, HIF-1 and HIF-2, are known to be stabilized at different oxygen levels and to have different temporal responses to hypoxia. Recently, stromal HIF-1 and HIF-2 have been suggested to have opposing roles in breast cancer progression. There is an established link between intralesional, severe hypoxia near areas of necrosis with high levels of HIF-1 and poor prognosis in breast cancer. However, the biological effects of moderate hypoxia and the hypoxic response of stromal cells are currently topics of intense investigation.

Loss of Cul1 results in early embryonic lethality and dysregulation of cyclin E.

The sequential timing of cell-cycle transitions is primarily governed by the availability and activity of key cell-cycle proteins. Recent studies in yeast have identified a class of ubiquitin ligases (E3 enzymes) called SCF complexes, which regulate the abundance of proteins that promote and inhibit cell-cycle progression at the G1-S phase transition. SCF complexes consist of three invariable components, Skp1, Cul-1 (Cdc53 in yeast) and Rbx1, and a variable F-box protein that recruits a specific cellular protein to the ubquitin pathway for degradation. To study the role of Cul-1 in mammalian development and cell-cycle regulation, we generated mice deficient for Cul1 and analysed null embryos and heterozygous cell lines. We show that Cul1 is required for early mouse development and that Cul1 mutants fail to regulate the abundance of the G1 cyclin, cyclin E (encoded by Ccne), during embryogenesis.

On the propagation of nonlinear waves in the atmosphere.

Starting from the general equations of fluid dynamics that describe the atmosphere, and using asymptotic methods, we present the derivation of the leading-order equations for nonlinear wave propagation in the troposphere. The only simplifying assumption is that the flow in the atmosphere exists in a thin shell over a sphere. The systematic approach adopted here enables us to find a consistent balance of terms describing the propagation, and to identify the temperature and pressure gradients that drive the motion, as well as the heat sources required. This produces a new nonlinear propagation equation that is then examined in some detail. With the morning glory in mind, we construct a few exact solutions, which, separately, describe breezes, bores and oscillatory motion.

Ischaemia-induced retinal neovascularisation and diabetic retinopathy in mice with conditional knockout of hypoxia-inducible factor-1 in retinal Müller cells.

AIMS/HYPOTHESIS: Retinal Müller cells are known to produce inflammatory and angiogenic cytokines, which play important roles in diabetic retinopathy. Hypoxia-inducible factor (HIF)-1 has been shown to play a crucial role in retinal inflammation and neovascularisation. We sought to determine the role of Müller cell-derived HIF-1 in oxygen-induced retinopathy (OIR) and diabetic retinopathy using conditional Hif-1α (also known as Hif1a) knockout (KO) mice. METHODS: Conditional Hif-1α KO mice were generated by crossing mice expressing cyclisation recombinase (cre, also known as P1_gp003) in Müller cells with floxed Hif-1α mice and used for OIR and streptozotocin-induced diabetes to induce retinal neovascularisation and inflammation, respectively. Abundance of HIF-1α and pro-angiogenic and pro-inflammatory factors was measured by immunoblotting and immunohistochemistry. Retinal neovascularisation was visualised by angiography and quantified by counting pre-retinal nuclei. Retinal inflammation was evaluated by leucostasis and vascular leakage. RESULTS: While the Hif-1α KO mice showed significantly decreased HIF-1α levels in the retina, they exhibited no apparent histological or visual functional abnormalities under normal conditions. Compared with wild-type counterparts, Hif-1α KO mice with OIR demonstrated attenuated overproduction of vascular endothelial growth factor (VEGF) and intercellular adhesion molecule (ICAM)-1, reduced vascular leakage and alleviated neovascularisation in the retina. Under diabetes conditions, disruption of Hif-1α in Müller cells attenuated the increases of retinal vascular leakage and adherent leucocytes, as well as the overproduction of VEGF and ICAM-1. CONCLUSIONS/INTERPRETATION: Müller cell-derived HIF-1α is a key mediator of retinal neovascularisation, vascular leakage and inflammation, the major pathological changes in diabetic retinopathy. Müller cell-derived HIF-1α is therefore a promising therapeutic target for diabetic retinopathy.

Biology of HIF-1alpha.

The increase in body size of humans and other vertebrates requires a physiological infrastructure to provide adequate delivery of oxygen to tissues and cells to maintain oxygen homeostasis. The heart, lungs and the vasculature are all part of a highly regulated system that ensures the distribution of the precise amount of oxygen needed throughout the mammalian organism. Given its fundamental impact on physiology and pathology, it is no surprise that the response of cells to a lack of oxygen, termed hypoxia, has been the focus of many research groups worldwide for many decades now. The transcriptional complex hypoxia-inducible factor has emerged as a key regulator of the molecular hypoxic response, mediating a wide range of physiological and cellular mechanisms necessary to adapt to reduced oxygen.

SPARC is a source of copper-binding peptides that stimulate angiogenesis.

SPARC is a transiently expressed extracellular matrix-binding protein that alters cell shape and regulates endothelial cell proliferation in vitro. In this study, we show that SPARC mRNA and protein are synthesized by endothelial cells during angiogenesis in vivo. SPARC and peptides derived from a cationic region of the protein (amino acids 113-130) stimulated the formation of endothelial cords in vitro; moreover, these peptides stimulated angiogenesis in vivo. Mapping of the active domain demonstrated that the sequence KGHK was responsible for most of the angiogenic activity; substitution of the His residue decreased the effect. We found that proteolysis of SPARC provided a source of KGHK, GHK, and longer peptides that contained these sequences. Although the Cu(2+)-GHK complex had been identified as a mitogen/morphogen in normal human plasma, we found KGHK and longer peptides to be potent stimulators of angiogenesis. SPARC113-130 and KGHK were shown to bind Cu2+ with high affinity; however, previous incubation with Cu2+ was not required for the stimulatory activity. Since a peptide from a second cationic region of SPARC (SPARC54-73) also bound Cu2+ but had no effect on angiogenesis, the angiogenic activity appeared to be sequence specific and independent of bound Cu2+. Thus, specific degradation of SPARC, a matrix-associated protein expressed by endothelial cells during vascular remodeling, releases a bioactive peptide or peptides, containing the sequence (K)GHK, that could regulate angiogenesis in vivo.

c-jun is essential for sympathetic neuronal death induced by NGF withdrawal but not by p75 activation.

Sympathetic neurons depend on NGF binding to TrkA for their survival during vertebrate development. NGF deprivation initiates a transcription-dependent apoptotic response, which is suggested to require activation of the transcription factor c-Jun. Similarly, apoptosis can also be induced by selective activation of the p75 neurotrophin receptor. The transcriptional dependency of p75-mediated cell death has not been determined; however, c-Jun NH2-terminal kinase has been implicated as an essential component. Because the c-jun-null mutation is early embryonic lethal, thereby hindering a genetic analysis, we used the Cre-lox system to conditionally delete this gene. Sympathetic neurons isolated from postnatal day 1 c-jun-floxed mice were infected with an adenovirus expressing Cre recombinase or GFP and analyzed for their dependence on NGF for survival. Cre immunopositive neurons survived NGF withdrawal, whereas those expressing GFP or those uninfected underwent apoptosis within 48 h, as determined by DAPI staining. In contrast, brain-derived neurotrophic factor (BDNF) binding to p75 resulted in an equivalent level of apoptosis in neurons expressing Cre, GFP, and uninfected cells. Nevertheless, cycloheximide treatment prevented BDNF-mediated apoptosis. These results indicate that whereas c-jun is required for apoptosis in sympathetic neurons on NGF withdrawal, an alternate signaling pathway must be induced on p75 activation.

Depletion of CD4+ T cells in major histocompatibility complex class II-deficient mice.

The maturation of T cells in the thymus is dependent on the expression of major histocompatibility complex (MHC) molecules. By disruption of the MHC class II Ab beta gene in embryonic stem cells, mice were generated that lack cell surface expression of class II molecules. These MHC class II-deficient mice were depleted of mature CD4+ T cells and were deficient in cell-mediated immune responses. These results provide genetic evidence that class II molecules are required for the maturation and function of mature CD4+ T cells.

Uncoupling of obesity from insulin resistance through a targeted mutation in aP2, the adipocyte fatty acid binding protein.

Fatty acid binding proteins (FABPs) are small cytoplasmic proteins that are expressed in a highly tissue-specific manner and bind to fatty acids such as oleic and retinoic acid. Mice with a null mutation in aP2, the gene encoding the adipocyte FABP, were developmentally and metabolically normal. The aP2-deficient mice developed dietary obesity but, unlike control mice, they did not develop insulin resistance or diabetes. Also unlike their obese wild-type counterparts, obese aP2-/- animals failed to express in adipose tissue tumor necrosis factor-alpha (TNF-alpha), a molecule implicated in obesity-related insulin resistance. These results indicate that aP2 is central to the pathway that links obesity to insulin resistance, possibly by linking fatty acid metabolism to expression of TNF-alpha.

Targeting of nonexpressed genes in embryonic stem cells via homologous recombination.

Gene targeting via homologous recombination-mediated disruption in murine embryonic stem (ES) cells has been described for a number of different genes expressed in these cells; it has not been reported for any nonexpressed genes. Pluripotent stem cell lines were isolated with homologously recombined insertions at three different loci: c-fos, which is expressed at a low level in ES cells, and two genes, adipsin and adipocyte P2 (aP2), which are transcribed specifically in adipose cells and are not expressed at detectable levels in ES cells. The frequencies at which homologous recombination events occurred did not correlate with levels of expression of the targeted genes, but did occur at rates comparable to those previously reported for genes that are actively expressed in ES cells. Injection of successfully targeted cells into mouse blastocysts resulted in the formation of chimeric mice. These studies demonstrate the feasibility of altering genes in ES cells that are expressed in a tissue-specific manner in the mouse, in order to study their function at later developmental stages.

An essential role for ectodomain shedding in mammalian development.

The ectodomains of numerous proteins are released from cells by proteolysis to yield soluble intercellular regulators. The responsible protease, tumor necrosis factor-alpha converting enzyme (TACE), has been identified only in the case when tumor necrosis factor-alpha (TNFalpha) is released. Analyses of cells lacking this metalloproteinase-disintegrin revealed an expanded role for TACE in the processing of other cell surface proteins, including a TNF receptor, the L-selectin adhesion molecule, and transforming growth factor-alpha (TGFalpha). The phenotype of mice lacking TACE suggests an essential role for soluble TGFalpha in normal development and emphasizes the importance of protein ectodomain shedding in vivo.

Loss of vascular endothelial growth factor expression reduces vascularization, but not growth, of tumors lacking the Von Hippel-Lindau tumor suppressor gene.

Individuals bearing germ line mutations in the Von Hippel-Lindau (VHL) tumor suppressor gene are predisposed to the development of highly angiogenic tumors. This is correlated with an increased expression of the angiogenic factor vascular endothelial growth factor (VEGF) in these tumors, which is in part caused by elevated expression of the HIF-1 hypoxia inducible transcription factors. We created malignant astrocytes with genetic deletions of the VHL gene and implanted them in subcutaneous and intracranial sites; these sites are respectively vessel poor and vessel-rich tissues. When grown in a vessel poor site, VEGF expression in VHL null cells was important for both vascularization and tumor growth. However, when the same cells are grown in the vessel-rich intracranial environment, loss of VEGF expression reduces vascularization, but does not affect tumor growth. This indicates that antiangiogenic therapies for tumors that express high levels of angiogenic factors such as VEGF may vary in their efficacy, with potentially lowered effectiveness in sites, such as the brain, that are inherently vessel rich.

Molecular cloning and characterization of retinal photoreceptor guanylyl cyclase-activating protein.

Guanylyl cyclase-activating protein (GCAP) is thought to mediate Ca(2+)-sensitive regulation of guanylyl cyclase (GC), a key event in recovery of the dark state of rod photoreceptors following light exposure. Here, we characterize GCAP from several vertebrate species by molecular cloning and provide evidence that GCAP contains a heterogeneously acylated N-terminal region that interacts with GC. Vertebrate GCAPs consist of 201-205 amino acids, and sequence analysis indicates the presence fo three EF hand Ca(2+)-binding motifs. These results establish that GCAP is a novel photoreceptor-specific member of a large family of Ca(2+)-binding proteins and suggest that it participates in the Ca(2+)-binding proteins and suggest that it participates in the Ca(2+)-sensitive activation of GC.

Angiogenesis: the role of the microenvironment in flipping the switch.

The initiating factors in angiogenesis during development and disease are often microenvironmental changes, which induce signaling to the vasculature from affected tissues. Among these, lowered oxygen pressure, hypoxia, is one of the most potent inducers/initiators of an angiogenic response. Significant evidence indicates that hypoxia acts as a morphogen during vascularization - inducing and shaping the recruitment and formation of new vascular beds through critical transcriptional control pathways. Recent advances indicate that extensive interactions occur between developing blood vessels, the tissues that they vascularize, and the interstitial environment to control and shape the establishment of new capillary beds. Identification of the processes that control the hypoxic response intracellularly has allowed an increasingly sophisticated understanding of angiogenesis as a process that is very closely tied to the microenvironment that it occurs in. Further understanding of these processes may present powerful therapeutic opportunities for disease intervention.

Isoforms of vascular endothelial growth factor act in a coordinate fashion To recruit and expand tumor vasculature.

Vascular endothelial growth factor (VEGF) is an essential regulator of vascularization. It is expressed as several splice variants; the major forms contain 120 amino acids, 164 amino acids, and 188 amino acids. We utilized transformed cells nullizygous for VEGF to specifically express each of these isoforms in isolation, in order to determine the role of each in tumorigenic neo-vascularization. We found that only the intermediate isoform, VEGF164, could fully rescue tumor growth; VEGF120 partially rescued tumor growth, and VEGF188 failed completely to rescue tumor expansion. Surprisingly, the vascular density of VEGF188 isoform-expressing tumors is significantly greater than that of wild-type VEGF cells and the other isoform-specific tumors. The failure of the hypervascular VEGF188-expressing tumors to grow may be due to inadequate perfusion of the massive number of microvessels in these tumors; three-dimensional imaging of the tumorigenic vasculature indicated little or no recruitment of the peripheral vasculature. This demonstrates that the VEGF isoforms perform unique functions which together enable tumorigenic vascularization.

Normal peripheral T-cell function in c-Fos-deficient mice.

The ubiquitous transcription factors Fos and Jun are rapidly induced in T cells stimulated through the T-cell antigen receptor and regulate transcription of cytokines, including interleukin 2, in activated T cells. Since positive and negative selection of thymocytes during T-cell development also depends on activation through the T-cell receptor, Fos and Jun may play a role in thymocyte development as well. Fos and Jun act at several regulatory elements in the interleukin 2 promoter, including the AP-1 and NFAT sites. Using antisera specific to individual Fos and Jun family members, we show that c-Fos as well as other Fos family members are present in the inducible AP-1 and NFAT complexes of activated murine T cells. Nevertheless, c-Fos is not absolutely required for the development or function of peripheral T cells, as shown by using mice in which both copies of the c-fos gene were disrupted by targeted mutagenesis. c-Fos-deficient mice were comparable to wild-type mice in their patterns of thymocyte development and in the ability of their peripheral T cells to proliferate and produce several cytokines in response to T-cell receptor stimulation. Our results suggest that other Fos family members may be capable of substituting functionally for c-Fos during T-cell development and cytokine gene transcription in activated T cells.