Multiple Cdk1 Inhibitory Kinases Regulate the Cell Cycle during Development

AbstractThe Wee kinases block entry into mitosis by phosphorylating and inhibiting the activity of the mitotic cyclin-dependent kinase, Cdk1. We have found that the various Xenopus Wee kinases have unique temporal and spatial patterns of expression during development. In addition, we have isolated and characterized a new Wee1-like kinase, Xenopus Wee2. By both in vivo and in vitro tests, Xenopus Wee2 functions as a Wee1-like kinase. The previously isolated Wee1-like kinase, Xenopus Wee1, is expressed only as maternal gene product. In contrast, Xenopus Wee2 is predominantly a zygotic gene product, while the third Wee kinase, Xenopus Myt1, is both a maternal and zygotic gene product. Concurrent with the changing levels of these Cdk inhibitory kinases, the pattern of embryonic cell division becomes asynchronous and spatially restricted in the Xenopus embryo. Interestingly, once zygotic transcription begins, Xenopus Wee2 is expressed in regions of the embryo that are devoid of mitotic cells, such as the involuting mesoderm. In contrast, Xenopus Myt1 is expressed in regions of the embryo that have high levels of proliferation, such as the developing neural tissues. The existence of multiple Wee kinases may help explain how distinct patterns of cell division arise and are regulated during development

Sound damping in ferrofluids: Magnetically enhanced compressional viscosity

The damping of sound waves in magnetized ferrofluids is investigated and shown to be considerably higher than in the non-magnetized case. This fact may be interpreted as a field-enhanced, effective compressional viscosity -- in analogy to the ubiquitous field-enhanced shear viscosity that is known to be the reason for many unusual behavior of ferrofluids under shear.Comment: 5 page

A silent H-bond can be mutationally activated for high-affinity interaction of BMP-2 and activin type IIB receptor

BACKGROUND: Bone morphogenetic proteins (BMPs) are key regulators in the embryonic development and postnatal tissue homeostasis in all animals. Loss of function or dysregulation of BMPs results in severe diseases or even lethality. Like transforming growth factors β (TGF-βs), activins, growth and differentiation factors (GDFs) and other members of the TGF-β superfamily, BMPs signal by assembling two types of serine/threonine-kinase receptor chains to form a hetero-oligomeric ligand-receptor complex. BMP ligand receptor interaction is highly promiscuous, i.e. BMPs bind more than one receptor of each subtype, and a receptor bind various ligands. The activin type II receptors are of particular interest, since they bind a large number of diverse ligands. In addition they act as high-affinity receptors for activins but are also low-affinity receptors for BMPs. ActR-II and ActR-IIB therefore represent an interesting example how affinity and specificity might be generated in a promiscuous background. RESULTS: Here we present the high-resolution structures of the ternary complexes of wildtype and a variant BMP-2 bound to its high-affinity type I receptor BMPR-IA and its low-affinity type II receptor ActR-IIB and compare them with the known structures of binary and ternary ligand-receptor complexes of BMP-2. In contrast to activin or TGF-β3 no changes in the dimer architecture of the BMP-2 ligand occur upon complex formation. Functional analysis of the ActR-IIB binding epitope shows that hydrophobic interactions dominate in low-affinity binding of BMPs; polar interactions contribute only little to binding affinity. However, a conserved H-bond in the center of the type II ligand-receptor interface, which does not contribute to binding in the BMP-2 – ActR-IIB interaction can be mutationally activated resulting in a BMP-2 variant with high-affinity for ActR-IIB. Further mutagenesis studies were performed to elucidate the binding mechanism allowing us to construct BMP-2 variants with defined type II receptor binding properties. CONCLUSION: Binding specificity of BMP-2 for its three type II receptors BMPR-II, Act-RII and ActR-IIB is encoded on single amino acid level. Exchange of only one or two residues results in BMP-2 variants with a dramatically altered type II receptor specificity profile, possibly allowing construction of BMP-2 variants that address a single type II receptor. The structure-/function studies presented here revealed a new mechanism, in which the energy contribution of a conserved H-bond is modulated by surrounding intramolecular interactions to achieve a switch between low- and high-affinity binding

Pathways and variability of the Antarctic Intermediate Water in the western equatorial Pacific Ocean.

In the western equatorial Pacific the low-salinity core of Antarctic Intermediate Water (AAIW) is found at about 800 m depth between potential density levels σθ = 27.2 and 27.3. The pathways of AAIW and the degradation of its core are studied, from the Bismarck Sea to the Caroline Basins and into the zonal equatorial current system. Both historical and new observational data, and results from numerical circulation model runs are used. The observations include hydrographic stations from German and Japanese research vessels, and Eulerian and Lagrangian current measurements. The model is the JAMSTEC high-resolution numerical model based on the Modular Ocean Model (MOM 2). The general agreement between results from the observations and from the model enables us to diagnose properties and to provide new information on the AAIW. The analysis confirms the paramount influence of topography on the spreading of the AAIW tongue north of New Guinea. Two cores of AAIW are found in the eastern Bismarck Sea. One core originates from Vitiaz Strait and one from St. George’s Channel, probably arriving on a cyclonic pathway. They merge in the western Bismarck Sea without much change in their total salt content, and the uniform core then increases considerably in salt content when subjected to mixing in the Caroline Basins. Hydrographic and moored current observations as well as model results show a distinct annual signal in salinity and velocity in the AAIW core off New Guinea. It appears to be related to the monsoonal change that is typically found in the near-surface waters in the region. Lagrangian data are used to investigate the structure of the deep New Guinea Coastal Undercurrent, the related cross-equatorial flow and eddy-structure, and the embedment in the zonal equatorial current system. Results from 17 neutrally buoyant RAFOS floats, ballasted to drift in the AAIW core layer, are compared with a numerical tracking experiment. In the model 73 particles are released at five-day intervals from Station J (2.5°N, 142°E), simulating currents at a moored time series station north of New Guinea. Observed and model track patterns are fairly consistent in space and season. Floats cross the equator preferably north of Cenderawasih Bay, with a maximum range in eddy-motion in this region north of New Guinea. The northward route at 135°E is also reflected in a low-salinity tongue reaching up to 3°N. At that longitude the floats seem to ignore the zonally aligned equatorial undercurrents. Farther to the east (139 145°E), however, the float observations are consistent with low-latitude bands of intermediate currents

Differential Inhibition of Constitutive and Inducible Nitric Oxide Synthase in Vascular Endothelial Cells by Analogues of Tetrahydrobiopterin

In the vasculature, a physiologic production of nitric oxide (NO) is maintained by endothelial nitric oxide synthase (eNOS). Induction of inducible nitric oxide synthase (ÍNOS) under inflammatory conditions (e.g. septic shock) resulting in high levels of nitric oxide (NO) is believed to be partly responsible for the pathophysiologic changes in the vascular system that occur under inflammatory conditions (e.g. septic shock). Both NOS isoforms are dependent on the obligatory cofactor tetrahydrobiopterin (BH4). We investigated the selectivity and potency of the BH4 analogues 4-amino-BH4 and 5-methyl-BH4 in inhibiting eNOS and iNOS in a murine vascular endothelial cell (MVEC) model expressing either eNOS or iNOS under physiologic and inflammatory conditions, respectively. Exogenous BH4 and its precursor sepiapterin both enhanced physiologic eNOS activity in resting MVEC, while 4-amino-BH4 slightly inhibited eNOS. 5-methyl-BH4 did not have any effect on eNOS. BH4, sepi - apterin, and 5-methyi-BH4 had no effect on iNOS in inflammatory activated MVEC. In contrast, 4-amino-BH4 selectively inhibited iNOS with a potency comparable to the unselective NOS inhibitor Νω-monomethyl-L-argimne (L-NMMA). The present study demonstrates that 4-amino-BH4 selectively and potently inhibits iNOS in vascular endothelial cells, while its effect on eNOS is minimal. The selective inhibition of iNOS is a promising strategy for the treatment of inflammatory conditions with high output of NO. Further in vivo studies are required to determine whether inhibition of NO production by analogues of BH4 offers any advantage compared to inhibition by L-arginine analogue

Long-term follow-up of acute changes in coronary artery diameter caused by Kawasaki disease: risk factors for development of stenotic lesions

Objective: To investigate the long-term outcome of initially dilated/aneurysmatic coronary arteries in Kawasaki disease (KD) and to define risk factors for significant myocardial ischemia during follow-up, we retrospectively followed all pediatric patients with proven acute coronary changes due to KD in our institution. Methods and results: Since 1981, 38 children have been identified with coronary changes due to KD. The median age was 1.2years (0.1-12.8). In 37 patients therapy with intravenous immunoglobulin was initiated within 9days (1-30) after the beginning of KD. All received aspirin and three additionally received steroids. Median follow-up was 8.5years (0.5-24.8). We defined two groups: A aneurysm/ectasia of the coronary artery ≤5.0mm (n=23) and B aneurysm size >5.0mm (n=15). During follow-up, all coronary aneurysms of group A regressed to normal size, whereas in 14 patients of group B (93%) the aneurysms persisted or even increased in size. Four patients of group B developed severe coronary stenosis at the proximal and/or distal end of the aneurysm and needed an intervention (endovascular balloon dilation and stent implantation (n=2) or bypass surgery (n=2)) after a median time interval of 9.8years (1.0-15.6) after KD. They all had ECG changes preceding the intervention about 1year in advance. Maximum aneurysm size >5mm was a statistical significant predictive risk factor for myocardial ischemia. Conclusions: After KD, patients with a coronary aneurysm size >5.0mm need close follow-up assessments because of an elevated risk for the development of coronary stenotic lesions. In case of new and even unspecific ECG changes, coronary imaging modalities (angiography, MRI) have to be considered. Therapy options vary from percutaneous catheter interventions to bypass surgery and have to be selected individually for each patien