On the Hydrodynamics of Anomalocaris Tail Fins.

Anomalocaris canadensis, a soft-bodied stem-group arthropod from the Burgess Shale, is considered the largest predator of the Cambrian period. Thanks to a series of lateral flexible lobes along its dorso-ventrally compressed body, it is generally regarded as an efficient swimmer, well-adapted to its predatory lifestyle. Previous theoretical hydrodynamic simulations have suggested a possible optimum in swimming performance when the lateral lobes performed as a single undulatory lateral fin, comparable to the pectoral fins in skates and rays. However, the role of the unusual fan-like tail of Anomalocaris has not been previously explored. Swimming efficiency and maneuverability deduced from direct hydrodynamic analysis are here studied in a towing tank facility using a three-vane physical model designed as an abstraction of the tail fin. Through direct force measurements, it was found that the model exhibited a region of steady-state lift and drag enhancement at angles of attack greater than 25° when compared with a triangular-shaped reference model. This would suggest that the resultant normal force on the tail fin of Anomalocaris made it well-suited for turning maneuvers, giving it the ability to turn quickly and through small radii of curvature. These results are consistent with an active predatory lifestyle, although detailed kinematic studies integrating the full organism, including the lateral lobes, would be required to test the effect of the tail fin on overall swimming performance. This study also highlights a possible example of evolutionary convergence between the tails of Anomalocaris and birds, which, in both cases, are well-adapted to efficient turning maneuvers.

On the high-lift characteristics of a bio-inspired, slotted delta wing.

A bio-inspired, slotted delta wing was abstracted from a multi-vane propulsor geometry ubiquitous in nature, and analysed to investigate aerodynamic performance during acceleratory and steady-state motions. Evolutionary convergence of slotted geometries in nature suggests an aerodynamic benefit in manoeuvrability, as exemplified in the fins and wings of a broad range of extant and extinct swimmers and flyers, respectively. Through direct force measurements and stereoscopic particle image velocimetry, it was found that the abstracted, slotted geometry exhibited a region of steady-state lift and drag enhancement at angles of attack greater than 25° when compared to a reference profile based on a delta-wing plate. At an angle of attack of 30°, the lift and drag measured on the abstracted model were 15.3% and 17.0% higher than the delta-wing model, respectively. In contrast, these shapes showed little difference in performance during an acceleration-from-rest manoeuvre. It was found that the secondary and tertiary vanes of the abstraction encouraged the formation of additional leading-edge vorticity. The formation of these additional leading-edge vortices was confirmed by an increase in streamwise circulation measured near each effective leading edge along the length of the chord. As such, this configuration provides lift augmentation appropriate for the development of high-performance control surfaces.

Transcriptional activation by NF-kappaB requires multiple coactivators.

Nuclear factor-kappaB (NF-kappaB) plays a role in the transcriptional regulation of genes involved in inflammation and cell survival. In this report we demonstrate that NF-kappaB recruits a coactivator complex that has striking similarities to that recruited by nuclear receptors. Inactivation of either cyclic AMP response element binding protein (CREB)-binding protein (CBP), members of the p160 family of coactivators, or the CBP-associated factor (p/CAF) by nuclear antibody microinjection prevents NF-kappaB-dependent transactivation. Like nuclear receptor-dependent gene expression, NF-kappaB-dependent gene expression requires specific LXXLL motifs in one of the p160 family members, and enhancement of NF-kappaB activity requires the histone acetyltransferase (HAT) activity of p/CAF but not that of CBP. This coactivator complex is differentially recruited by members of the Rel family. The p50 homodimer fails to recruit coactivators, although the p50-p65 heterodimeric form of the transcription factor assembles the integrator complex. These findings provide new mechanistic insights into how this family of dimeric transcription factors has a differential effect on gene expression.

Nuclear integration of glucocorticoid receptor and nuclear factor-kappaB signaling by CREB-binding protein and steroid receptor coactivator-1.

The p65 (RelA) component of nuclear factor-kappaB (NF-kappaB) and the glucocorticoid receptor (GR) mutually repress each other's ability to activate transcription. Both of these transcriptional activators depend upon the coactivators CREB-binding protein (CBP) and steroid receptor coactivator-1 (SRC-1) for maximal activity. Here we show that increased levels of CBP relieves the inhibition of glucocorticoid-mediated repression of NF-kappaB activity and the NF-kappaB-mediated repression of GR activity. SRC-1 can relieve the NF-kappaB-mediated repression of GR activity. We propose that cross-talk between the p65 component of NF-kappaB and glucocorticoid receptors is due, at least in part, to nuclear competition for limiting amounts of the coactivators CBP and SRC-1, thus providing a novel mechanism for decreasing expression of genes involved in the inflammatory response.

Effects of supplemental vitamin E and canola oil on tissue tocopherol and liver fatty acid profile of finishing swine.

We conducted a 4 x 3 factorial experiment with finishing pigs for 6 wk to evaluate effects of dietary canola oil and vitamin E on vitamin E status and liver fatty acid profile. Treatments consisted of four supplemental levels of vitamin E (0, 50, 125, and 200 mg/kg) and three of canola oil (0, 5, and 10% of the diet). Serum was collected each week and tissue samples at d 42. Dietary canola oil (P = .02) and vitamin E (P < .001) increased serum alpha-tocopherol. Serum alpha-tocopherol reached a plateau at d 35 of vitamin E and canola oil supplementation. An interaction was observed between canola oil and vitamin E (P = .02) for liver alpha-tocopherol. Liver alpha-tocopherol was greater in pigs fed diets with 10% canola oil and supplemented with 125 or 200 mg/kg of vitamin E than in pigs fed diets with 0 and 5% canola oil. An interaction also occurred between canola oil and vitamin E (P = .01) for alpha-tocopherol in the gluteus medius and obliquus capitis caudalis muscles. A greater magnitude of increase in muscle alpha-tocopherol was observed in pigs fed diets with no canola oil than in pigs fed diets with 5 and 10% canola oil. Highest alpha-tocopherol was in liver, followed by obliquus capitis caudalis and then gluteus medius. Inclusion of 5 or 10% dietary canola oil decreased the amount of saturated fatty acids by 4.1 and 13.5%, increased monounsaturated fatty acids by 10.9 and 39.3%, respectively, and had no effect (P > .10) on total polyunsaturated fatty acids. Canola oil increased linoleic acid [18:2(n-6)] (quadratic, P = .05) and linolenic acid [18:3(n-3)] (linear, P < .001) while decreasing arachidonic acid [20:4(n-6)] and docosadienoic acid (20:2) linearly (P < .001 and P = .02, respectively). Dietary canola oil and vitamin E increased serum and tissue alpha-tocopherol; canola oil increased monounsaturated and decreased saturated fatty acids in liver.

HBP1: a HMG box transcriptional repressor that is targeted by the retinoblastoma family.

A prominent feature of cell differentiation is the initiation and maintenance of an irreversible cell cycle arrest with the complex involvement of the retinoblastoma (RB) family (RB, p130, p107). We have isolated the HBP1 transcriptional repressor as a potential target of the RB family in differentiated cells. By homology, HBP1 is a sequence-specific HMG transcription factor, of which LEF-1 is the best-characterized family member. Several features of HBP1 suggest an intriguing role as a transcriptional and cell cycle regulator in differentiated cells. First, inspection of the HBP1 protein sequence revealed two consensus RB interaction motifs (LXCXE and IXCXE). Second, HBP1 interaction was selective for RB and p130, but not p107. HBP1, RB, and p130 levels are all up-regulated with differentiation; in contrast, p107 levels decline. Third, HBP1 can function as a transcriptional repressor of the promoter for N-MYC, which is a critical cell cycle and developmental gene. Fourth, because the activation of the N-MYC promoter in cycling cells required the E2F transcription factor, we show that E2F-1 and HBP1 represent opposite transcriptional signals that can be integrated within the N-MYC promoter. Fifth, the expression of HBP1 lead to efficient cell cycle arrest. The arrest phenotype was manifested in the presence of optimal proliferation signals, suggesting that HBP1 exerted a dominant regulatory role. Taken together, the results suggest that HBP1 may represent a unique transcriptional repressor with a role in initiation and establishment of cell cycle arrest during differentiation.

Cyclin A/CDK2 binds directly to E2F-1 and inhibits the DNA-binding activity of E2F-1/DP-1 by phosphorylation.

E2F-1, a member of the E2F transcription factor family, contributes to the regulation of the G1-to-S phase transition in higher eukaryotic cells. E2F-1 forms a heterodimer with DP-1 and binds to several cell cycle regulatory proteins, including the retinoblastoma family (RB, p107, p130) and cyclin A/CDK2 complexes. We have analyzed E2F-1 phosphorylation and its interaction with cyclin A/CDK2 complexes both in vivo and in vitro. In vitro, E2F-1 formed a stable complex with cyclin A/CDK2 but not with either subunit alone. DP-1 did not interact with cyclin A, CDK2, or the cyclin A/CDK2 complex. While the complex of cyclin A/CDK2 was required for stable complex formation with E2F-1, the kinase-active form of CDK2 was not required. However, E2F-1 was phosphorylated by cyclin A/CDK2 in vitro and was phosphorylated in vivo in HeLa cells. Two-dimensional tryptic phosphopeptide mapping studies demonstrated an overlap in the phosphopeptides derived from E2F-1 labeled in vitro and in vivo, indicating that cyclin A/CDK2 may be responsible for the majority of E2F-1 phosphorylation in vivo. Furthermore, an active DNA-binding complex could be reconstituted from purified E2F-1/DP-1 and cyclin A/CDK2. Binding studies conducted both in vitro and in vivo demonstrated that the cyclin A/CDK2-binding region resided within the N-terminal 124 amino acids of E2F-1. Because the stable association of E2F-1 with cyclin A/CDK2 in vitro and in vivo did not require a DP-1- or RB-binding domain and because the interactions could be reconstituted from purified components in vitro, we conclude that the interactions between cyclin A/CDK2 and E2F-1 are direct. Finally, we report that the DNA-binding activity of the E2F-1/DP-1 complex is inhibited following phosphorylation by cyclin A/CDK2.

The retinoblastoma protein region required for interaction with the E2F transcription factor includes the T/E1A binding and carboxy-terminal sequences.

Recent experiments in understanding the mechanism of the retinoblastoma protein (RB) function have revealed the existence of several cellular proteins that are complexed with RB. One of these cellular proteins is the E2F transcription factor, which was originally identified due to its inducibility by E1A during an adenovirus infection. The E2F recognition sequence is found in the promoters of several cellular genes involved in growth control, including several oncogenes. In this report, we provide evidence that the interaction of E2F and RB is mediated through a region on RB where viral oncogenes such as SV40 T antigen and adenovirus E1A bind and where tumorigenic mutations also cluster. Additional carboxy-terminal sequences are also required for the interaction with E2F. These observations provide evidence for a direct connection between tumor suppressor function and the gene expression program leading to cellular growth regulation.

Lipoxin generation by human megakaryocyte-induced 12-lipoxygenase.

Eicosanoid biosynthesis was examined with a human megakaryocytic cell line (Dami). Megakaryocytes incubated with [1-14C]arachidonic acid and either ionophore A23187 or thrombin generated both thromboxane and 12-hydroxyheptadecatrienoic acid (HHTrE). Exposure to phorbol myristate acetate (PMA) for 1 through 9 days induced differentiation and revealed an increase in the conversion of [1-14C]arachidonate to cyclooxygenase- and lipoxygenase (LO)-derived products. The LO-derived product was identified as 12S-HETE by its physical characteristics including GC/MS and chiral column SP-HPLC. PMA-treated Dami cells did not generate 5-HETE, leukotrienes or lipoxins from exogenous arachidonic acid while they did convert leukotriene A4 (LTA4) to lipoxin A4, lipoxin B4 and their respective all-trans isomers. In addition, COS-M6 cells transfected with a human 12-lipoxygenase cDNA and incubated with either arachidonic acid or LTA4 generated 12-HETE and lipoxins, respectively. The lipoxin profile generated by transfected COS-M6 cells incubated with LTA4 was similar to that generated by the PMA-treated Dami cells. Results indicate that human megakaryocytes can transform arachidonate and LTA4 to bioactive eicosanoids and that the 12-lipoxygenase appears upon further differentiation of these cells. In addition, they indicate that the 12-LO of human megakaryocytes and the 12-LO expressed by transfected COS cells can generate both lipoxins A4 and B4. Together they suggest that the human 12-LO can serve as a model of LX-synthetase activity with LTA4.

Lipoxin formation during human neutrophil-platelet interactions. Evidence for the transformation of leukotriene A4 by platelet 12-lipoxygenase in vitro.

Human neutrophils from peripheral blood may physically interact with platelets in several settings including hemostasis, inflammation, and a variety of vascular disorders. A role for lipoxygenase (LO)-derived products has been implicated in each of these events; therefore, we investigated the formation of lipoxins during coincubation of human neutrophils and platelets. Simultaneous addition of FMLP and thrombin to coincubations of these cells led to formation of both lipoxin A4 and lipoxin B4, which were monitored by reversed-phase high pressure liquid chromatography. Neither stimulus nor cell type alone induced the formation of these products. When leukotriene A4 (LTA4), a candidate for the transmitting signal, was added to platelets, lipoxins were formed. In cell-free 100,000 g supernatants of platelet lysates, which displayed 12-LO activity, LTA4 was also transformed to lipoxins. Platelet formation of lipoxins was inhibited by the LO inhibitor esculetin and partially sensitive to chelation of Ca2+, while neither acetylsalicylic acid nor indomethacin significantly inhibited their generation. In contrast, neutrophils did not transform LTA4 to lipoxins. Cell-free 100,000 g supernatants of neutrophil lysates converted LTA4 to LTB4. These results indicate that neutrophil-platelet interactions can lead to the formation of lipoxins from endogenous sources and provide a role for platelet 12-LO in the formation of lipoxins from LTA4.

Altitude and anesthesia.

The author describes the physiological changes that occur and the anesthetic considerations necessary at increased altitudes and under concomitant low barometric pressure levels, pointing out the differences between the acclimatized and the unacclimatized patient. Drawing from the literature and personal experience, the author explores the altered behavior of respiratory gases and anesthetic agents at increased altitudes.