Increased insulin sensitivity and obesity resistance in mice lacking the protein tyrosine phosphatase-1B gene

Protein tyrosine phosphatase-1B (PTP-1B) has been implicated in the negative regulation of insulin signaling. Disruption of the mouse homolog of the gene encoding PTP-1B yielded healthy mice that, in the fed state, had blood glucose concentrations that were slightly lower and concentrations of circulating insulin that were one-half those of their PTP-1B+/+ littermates. The enhanced insulin sensitivity of the PTP-1B-/- mice was also evident in glucose and insulin tolerance tests. The PTP-1B-/- mice showed increased phosphorylation of the insulin receptor in liver and muscle tissue after insulin injection in comparison to PTP-1B+/+ mice. On a high-fat diet, the PTP-1B-/- and PTP-1B+/- mice were resistant to weight gain and remained insulin sensitive, whereas the PTP-1B+/+ mice rapidly gained weight and became insulin resistant. These results demonstrate that PTP-1B has a major role in modulating both insulin sensitivity and fuel metabolism, thereby establishing it as a potential therapeutic target in the treatment of type 2 diabetes and obesity.

Pharmacodynamic evaluation of factors associated with the development of bacterial resistance in acutely ill patients during therapy

The selection of bacterial resistance was examined in relationship to antibiotic pharmacokinetics (PK) and organism MICs in the patients from four nosocomial lower respiratory tract infection clinical trials. The evaluable database included 107 acutely ill patients, 128 pathogens, and five antimicrobial regimens. Antimicrobial pharmacokinetics were characterized by using serum concentrations, and culture and sensitivity tests were performed daily on tracheal aspirates to examine resistance. Pharmacodynamic (PD) models were developed to identify factors associated with the probability of developing bacterial resistance. Overall, in 32 of 128 (25%) initially susceptible cases resistance developed during therapy. An initial univariate screen and a classification and regression tree analysis identified the ratio of the area under the concentration-time curve from 0 to 24 h to the MIC (AUC[0-24]/MIC) as a significant predictor of the development of resistance (P < 0.001). The final PK/PD model, a variant of the Hill equation, demonstrated that the probability of developing resistance during therapy increased significantly when antimicrobial exposure was at an AUC[0-24]/MIC ratio of less than 100. This relationship was observed across all treatments and within all organism groupings, with the exception of beta-lactamase-producing gram-negative organisms (consistent with type I beta-lactamase producers) treated with beta-lactam monotherapy. Combination therapy resulted in much lower rates of resistance than monotherapy, probably because all of the combination regimens examined had an AUC[0-24]/MIC ratio in excess of 100. In summary, the selection of antimicrobial resistance appears to be strongly associated with suboptimal antimicrobial exposure, defined as an AUC[0-24]MIC ratio of less than 100.

TYK2 and JAK2 are substrates of protein-tyrosine phosphatase 1B

The reversible tyrosine phosphorylation of proteins, modulated by the coordinated actions of protein-tyrosine kinases and protein-tyrosine phosphatases (PTPs), regulates the cellular response to a wide variety of stimuli. It is established that protein kinases possess discrete sets of substrates and that substrate recognition is often dictated by the presence of consensus phosphorylation sites. Here, we have extended this concept to the PTPs and demonstrated that (E/D)-pY-pY-(R/K) is a consensus substrate recognition motif for PTP1B. We have shown that JAK2 and TYK2 are substrates of PTP1B and that the substrate recognition site within theses kinases is similar to the site of dephosphorylation previously identified within the insulin receptor. A substrate-trapping mutant of PTP1B formed a stable interaction with JAK2 and TYK2 in response to interferon stimulation. Expression of wild type or substrate-trapping mutant PTP1B inhibited interferon-dependent transcriptional activation. Finally, mouse embryo fibroblasts deficient in PTP1B displayed subtle changes in tyrosine phosphorylation, including hyperphosphorylation of JAK2. The closely related JAK family member, JAK1, which does not match the consensus dephosphorylation site, was not recognized as a substrate. These data illustrate that PTP1B may be an important physiological regulator of cytokine signaling and that it may be possible to derive consensus substrate recognition motifs for other members of the PTP family, which may then be used to predict novel physiological substrates.

Adipose tissue reduction in mice lacking the translational inhibitor 4E-BP1

All nuclear-encoded mRNAs contain a 5' cap structure (m7GpppN, where N is any nucleotide), which is recognized by the eukaryotic translation initiation factor 4E (eIF4E) subunit of the eIF4F complex. The eIF4E-binding proteins constitute a family of three polypeptides that reversibly repress cap-dependent translation by binding to eIF4E, thus preventing the formation of the eIF4F complex. We investigated the biological function of 4E-BP1 by disrupting its gene (Eif4ebp1) in the mouse. Eif4ebp1-/- mice manifest markedly smaller white fat pads than wild-type animals, and knockout males display an increase in metabolic rate. The males' white adipose tissue contains cells that exhibit the distinctive multilocular appearance of brown adipocytes, and expresses the uncoupling protein 1 (UCP1), a specific marker of brown fat. Consistent with these observations, translation of the peroxisome proliferator-activated receptor-gamma co-activator 1 (PGC1), a transcriptional co-activator implicated in mitochondrial biogenesis and adaptive thermogenesis, is increased in white adipose tissue of Eif4ebp1-/- mice. These findings demonstrate that 4E-BP1 is a novel regulator of adipogenesis and metabolism in mammals.

The Syk protein tyrosine kinase is essential for Fcgamma receptor signaling in macrophages and neutrophils

The cytoplasmic protein tyrosine kinase Syk has two amino-terminal SH2 domains that engage phosphorylated immunoreceptor tyrosine-based activation motifs in the signaling subunits of immunoreceptors. Syk, in conjunction with Src family kinases, has been implicated in immunoreceptor signaling in both lymphoid and myeloid cells. We have investigated the role of Syk in Fcgamma receptor (FcgammaR)-dependent and -independent responses in bone marrow-derived macrophages and neutrophils by using mouse radiation chimeras reconstituted with fetal liver cells from Syk-/- embryos. Chimeric mice developed an abdominal hemorrhage starting 2 to 3 months after transplantation that was ultimately lethal. Syk-deficient neutrophils derived from the bone marrow were incapable of generating reactive oxygen intermediates in response to FcgammaR engagement but responded normally to tetradecanoyl phorbol acetate stimulation. Syk-deficient macrophages were defective in phagocytosis induced by FcgammaR but showed normal phagocytosis in response to complement. The tyrosine phosphorylation of multiple cellular polypeptides, including the FcgammaR gamma chain, as well as Erk2 activation, was compromised in Syk-/- macrophages after FcgammaR stimulation. In contrast, the induction of nitric oxide synthase in macrophages stimulated with lipopolysaccharide and gamma interferon was not dependent on Syk. Surprisingly, Syk-deficient macrophages were impaired in the ability to survive or proliferate on plastic petri dishes. Taken together, these results suggest that Syk has specific physiological roles in signaling from FcgammaRs in neutrophils and macrophages and raise the possibility that in vivo, Syk is involved in signaling events other than those mediated by immunoreceptors.

Rearrangements of the cellular p53 gene in erythroleukaemic cells transformed by Friend virus

There is now good evidence that the cellular protein, p53, is involved in the transformation process, although its precise role is unknown. It was reported recently that expression of the p53 gene can immortalize cells and that the p53 gene can replace the myc oncogene in a myc-ras immortalization/transformation assay. We have investigated whether p53 is involved in the progression towards the neoplastic state in vivo and report here that erythroleukaemic cell lines transformed by different isolates of Friend leukaemia virus show altered expression of the cellular p53 gene. High levels of p53 protein are found in certain lines, but the protein is undetectable in others. This heterogeneity in p53 gene expression is associated with heterogeneity in tumorigenicity. We demonstrate that genomic rearrangements are responsible for p53 gene inactivation in these cell lines and that they occur in vivo during the natural progression of Friend virus-induced erythroleukaemia.

Alteration in nicotine binding sites in Parkinson's disease, Lewy body dementia and Alzheimer's disease: possible index of early neuropathology

High-affinity nicotine binding, considered to primarily reflect the presence of CNS alpha 4 beta 2 nicotinic receptor subunits, was examined autoradiographically in brain regions most severely affected by Alzheimer and Parkinson types of pathology. In the midbrain, the high density of binding associated with the pars compacta of the substantia nigra was extensively reduced (65-75%, particularly in the lateral portion) in both Lewy body dementia and Parkinson's disease. Since loss of dopaminergic neurons in Lewy body dementia was only moderate (40%), loss or down-regulation of the nicotinic receptor may precede degeneration of dopaminergic neurons in this region. In the dorsolateral tegmentum, where diffuse cholinergic perikarya are located, nicotine binding was highly significantly decreased in both Lewy body dementia and Parkinson's disease with almost no overlap between the normal and disease groups, indicative of a major pathological involvement in or around the pedunculopontine cholinergic neurons. In the hippocampus, binding was decreased around the granular layer in Lewy body dementia and Alzheimer's disease, although unchanged in the stratum lacunosum moleculare, where binding was relatively higher. Dense bands of receptor binding in the presubiculum and parahippocampal gyrus--areas of highest binding in human cortex--were diminished in Alzheimer's disease but not Lewy body dementia. In temporal neocortex there were reductions in Alzheimer's disease throughout the cortical layers but in Lewy body dementia only in lower layers, in which Lewy bodies are concentrated. Abnormalities of the nicotinic receptor in the diseases examined appear to be closely associated with primary histopathological changes: dopaminergic cell loss in Parkinson's disease and Lewy body dementia, amyloid plaques and tangles in subicular and entorhinal areas in Alzheimer's disease. Loss or down-regulation of the receptor may precede neurodegeneration.

Three-dimensional organization of a human water channel

Aquaporins (AQP) are members of the major intrinsic protein (MIP) superfamily of integral membrane proteins and facilitate water transport in various eukaryotes and prokaryotes. The archetypal aquaporin AQP1 is a partly glycosylated water-selective channel that is widely expressed in the plasma membranes of several water-permeable epithelial and endothelial cells. Here we report the three-dimensional structure of deglycosylated, human erythrocyte AQP1, determined at 7 A resolution in the membrane plane by electron crystallography of frozen-hydrated two-dimensional crystals. The structure has an inplane, intramolecular 2-fold axis of symmetry located in the hydrophobic core of the bilayer. The AQP1 monomer is composed of six membrane-spanning, tilted alpha-helices. These helices form a barrel that encloses a vestibular region leading to the water-selective channel, which is outlined by densities attributed to the functionally important NPA boxes and their bridges to the surrounding helices. The intramolecular symmetry within the AQP1 molecule represents a new motif for the topology and design of membrane protein channels, and is a simple and elegant solution to the problem of bidirectional transport across the bilayer.

Shc proteins are phosphorylated and regulated by the v-Src and v-Fps protein-tyrosine kinases

The mammalian shc gene encodes two overlapping proteins of 46 and 52 kDa, each with a C-terminal Src homology 2 (SH2) domain and an N-terminal glycine/proline-rich sequence, that induce malignant transformation when overexpressed in mouse fibroblasts. p46shc, p52shc, and an additional 66-kDa shc gene product become highly tyrosine phosphorylated in Rat-2 cells transformed by the v-src or v-fps oncogene. Experiments using temperature-sensitive v-src and v-fps mutants indicate that Shc tyrosine phosphorylation is rapidly induced upon activation of the v-Src or v-Fps tyrosine kinases. These results suggest that Shc proteins may be directly phosphorylated by the v-Src and v-Fps oncoproteins in vivo. In cells transformed by v-src or v-fps, or in normal cells stimulated with epidermal growth factor, Shc proteins complex with a poorly phosphorylated 23-kDa polypeptide (p23). Activated tyrosine kinases therefore regulate the association of Shc proteins with p23 and may thereby control the stimulation of an Shc-mediated signal transduction pathway. The efficient phosphorylation of Shc proteins and the apparent induction of their p23-binding activity in v-src- and v-fps-transformed cells are consistent with the proposition that the SH2-containing Shc polypeptides are biologically relevant substrates of the oncogenic v-Src and v-Fps tyrosine kinases.

NEAR at eros: imaging and spectral results

Eros is a very elongated (34 kilometers by 11 kilometers by 11 kilometers) asteroid, most of the surface of which is saturated with craters smaller than 1 kilometer in diameter. The largest crater is 5.5 kilometers across, but there is a 10-kilometer saddle-like depression with attributes of a large degraded crater. Surface lineations, both grooves and ridges, are prominent on Eros; some probably exploit planes of weakness produced by collisions on Eros and/or its parent body. Ejecta blocks (30 to 100 meters across) are abundant but not uniformly distributed over the surface. Albedo variations are restricted to the inner walls of certain craters and may be related to downslope movement of regolith. On scales of 200 meters to 1 kilometer, Eros is more bland in terms of color variations than Gaspra or Ida. Spectra (800 to 2500 nanometers) are consistent with an ordinary chondrite composition for which the measured mean density of 2.67 +/- 0.1 grams per cubic centimeter implies internal porosities ranging from about 10 to 30 percent.

Vasovagal reactions may occur after orthotopic heart transplantation

OBJECTIVES

This study evaluated the ability of patients to manifest vasovagal reactions after orthotopic heart transplantation.

BACKGROUND

Paradoxic stimulation of left ventricular baroreceptors may be the afferent limb of the vasovagal reflex in humans. Orthotopic heart transplantation causes surgical denervation of these receptors and would therefore be expected to abolish the vasovagal reflex.

METHODS

To attempt to confirm this hypothesis, 10 patients with orthotopic heart transplantation underwent both head-up tilt testing while resting on a saddle support and testing for parasympathetic innervation of the donor heart before and after atropine infusion. Native and donor heart sinus rates were monitored by using an esophageal pill electrode throughout tilting and during parasympathetic testing.

RESULTS

Unexpectedly, seven patients had vasovagal responses at saddle support tilt testing, during which native heart rate decreased by 25 +/- 7 beats/min and mean arterial blood pressure decreased by 55 +/- 9 mm Hg. In three of these patients, there was also a decrease in donor heart rate of 23 +/- 26 beats/min. Parasympathetic testing showed possible evidence of donor heart vagal reinnervation in these patients with donor heart bradycardia during tilt but not in those with vasovagal reactions to tilt without slowing of the donor heart rate.

CONCLUSIONS

Vagal efferent reinnervation can occur after orthotopic heart transplantation in humans. However, the absence of such reinnervation in some patients with vasovagal responses to tilt calls into question the role of left ventricular receptors in inducing the vasovagal reaction.

Evidence for DNA-PK-dependent and -independent DNA double-strand break repair pathways in mammalian cells as a function of the cell cycle

Mice homozygous for the scid (severe combined immune deficiency) mutation are defective in the repair of DNA double-strand breaks (DSBs) and are consequently very X-ray sensitive and defective in the lymphoid V(D)J recombination process. Recently, a strong candidate for the scid gene has been identified as the catalytic subunit of the DNA-dependent protein kinase (DNA-PK) complex. Here, we show that the activity of the DNA-PK complex is regulated in a cell cycle-dependent manner, with peaks of activity found at the G1/early S phase and again at the G2 phase in wild-type cells. Interestingly, only the deficit of the G1/early S phase DNA-PK activity correlated with an increased hypersensitivity to X-irradiation and a DNA DSB repair deficit in synchronized scid pre-B cells. Finally, we demonstrate that the DNA-PK activity found at the G2 phase may be required for exit from a DNA damage-induced G2 checkpoint arrest. These observations suggest the presence of two pathways (DNA-PK-dependent and -independent) of illegitimate mammalian DNA DSB repair and two distinct roles (DNA DSB repair and G2 checkpoint traversal) for DNA-PK in the cellular response to ionizing radiation.

Fostriecin, an antitumor antibiotic with inhibitory activity against serine/threonine protein phosphatases types 1 (PP1) and 2A (PP2A), is highly selective for PP2A

Fostriecin, an antitumor antibiotic produced by Streptomyces pulveraceus, is a strong inhibitor of type 2A (PP2A; IC50 3.2 nM) and a weak inhibitor of type 1 (PP1; IC50 131 microM) serine/threonine protein phosphatases. Fostriecin has no apparent effect on the activity of PP2B, and dose-inhibition studies conducted with whole cell homogenates indicate that fostriecin also inhibits the native forms of PP1 and PP2A. Studies with recombinant PP1/PP2A chimeras indicate that okadaic acid and fostriecin have different binding sites.

The landing of the NEAR-Shoemaker spacecraft on asteroid 433 Eros

The NEAR-Shoemaker spacecraft was designed to provide a comprehensive characterization of the S-type asteroid 433 Eros (refs 1,2,3), an irregularly shaped body with approximate dimensions of 34 x 13 x 13 km. Following the completion of its year-long investigation, the mission was terminated with a controlled descent to its surface, in order to provide extremely high resolution images. Here we report the results of the descent on 12 February 2001, during which 70 images were obtained. The landing area is marked by a paucity of small craters and an abundance of 'ejecta blocks'. The properties and distribution of ejecta blocks are discussed in a companion paper. The last sequence of images reveals a transition from the blocky surface to a smooth area, which we interpret as a 'pond'. Properties of the 'ponds' are discussed in a second companion paper. The closest image, from an altitude of 129 m, shows the interior of a 100-m-diameter crater at 1-cm resolution.

Genome-wide association study meta-analysis of European and Asian-ancestry samples identifies three novel loci associated with bipolar disorder

Meta-analyses of bipolar disorder (BD) genome-wide association studies (GWAS) have identified several genome-wide significant signals in European-ancestry samples, but so far account for little of the inherited risk. We performed a meta-analysis of ∼750,000 high-quality genetic markers on a combined sample of ∼14,000 subjects of European and Asian-ancestry (phase I). The most significant findings were further tested in an extended sample of ∼17,700 cases and controls (phase II). The results suggest novel association findings near the genes TRANK1 (LBA1), LMAN2L and PTGFR. In phase I, the most significant single nucleotide polymorphism (SNP), rs9834970 near TRANK1, was significant at the P=2.4 × 10(-11) level, with no heterogeneity. Supportive evidence for prior association findings near ANK3 and a locus on chromosome 3p21.1 was also observed. The phase II results were similar, although the heterogeneity test became significant for several SNPs. On the basis of these results and other established risk loci, we used the method developed by Park et al. to estimate the number, and the effect size distribution, of BD risk loci that could still be found by GWAS methods. We estimate that >63,000 case-control samples would be needed to identify the ∼105 BD risk loci discoverable by GWAS, and that these will together explain <6% of the inherited risk. These results support previous GWAS findings and identify three new candidate genes for BD. Further studies are needed to replicate these findings and may potentially lead to identification of functional variants. Sample size will remain a limiting factor in the discovery of common alleles associated with BD.

NEAR's flyby of 253 mathilde: images of a C asteroid

On 27 June 1997, the Near Earth Asteroid Rendezvous (NEAR) spacecraft flew within 1212 kilometers of asteroid 253 Mathilde. Mathilde is an irregular, heavily cratered body measuring 66 kilometers by 48 kilometers by 46 kilometers. The asteroid's surface is dark (estimated albedo between 0.035 and 0.050) and similar in color to some CM carbonaceous chondrites. No albedo or color variations were detected. The volume derived from the images and the mass from Doppler tracking of the spacecraft yield a mean density of 1.3 +/- 0.2 grams per cubic centimeter, about half that of CM chondrites, indicating a porous interior structure.

Immunosuppressant pharmacokinetics and dosing modifications in HIV-1 infected liver and kidney transplant recipients

Solid organ transplantation in human immunodeficiency virus (HIV)-infected individuals requiring concomitant use of immunosuppressants (IS) (e.g. cyclosporine [CsA], sirolimus [SrL], tacrolimus [FK]) and antiretrovirals (ARVs) (e.g. protease inhibitors [PIs] and/or nonnucleoside reverse transcriptase inhibitors [NNRTIs]) is complicated by significant drug interactions. To assist in appropriate clinical management, we describe the pharmacokinetics and dosing modifications in 35 patients (20 kidney, 13 liver and two kidney-liver HIV-infected subjects with end-stage kidney or liver disease), on both IS and NNRTIs, PIs, and combined NNRTIs + PIs, in studies done at weeks 2-4 and/or 12 weeks after transplantation or after a change in IS or ARV drug regimen (n = 97 studies). CsA, SrL and FK concentrations were measured in whole blood by LC/MS. HIV-infected transplant recipients using PIs with IS had marked increases in CsA, FK or SrL trough levels compared to those on NNRTIs alone or to patients not on ARVs, necessitating either a reduction in dose or an increase in dosing interval. Subjects on efavirenz (EFV) and CsA required much higher doses of CsA than those using any other ARV. Changes in antiretroviral therapy should be carefully managed to avoid insufficient immunosuppression or toxicity due to drug interactions.

Dephosphorylation of cyclin-dependent kinases by type 2C protein phosphatases

Activating phosphorylation of cyclin-dependent protein kinases (CDKs) is necessary for their kinase activity and cell cycle progression. This phosphorylation is carried out by the Cdk-activating kinase (CAK); in contrast, little is known about the corresponding protein phosphatase. We show that type 2C protein phosphatases (PP2Cs) are responsible for this dephosphorylation of Cdc28p, the major budding yeast CDK. Two yeast PP2Cs, Ptc2p and Ptc3p, display Cdc28p phosphatase activity in vitro and in vivo, and account for approximately 90% of Cdc28p phosphatase activity in yeast extracts. Overexpression of PTC2 or PTC3 results in synthetic lethality in strains temperature-sensitive for yeast CAK1, and disruptions of PTC2 and PTC3 suppress the growth defect of a cak1 mutant. Furthermore, PP2C-like enzymes are the predominant phosphatases toward human Cdk2 in HeLa cell extracts, indicating that the substrate specificity of PP2Cs toward CDKs is evolutionarily conserved.

p38 MAP kinase mediates nitric oxide-induced apoptosis of neural progenitor cells

Neural progenitor cells (NPC) can proliferate, differentiate into neurons or glial cells, or undergo a form of programmed cell death called apoptosis. Although death of NPC occurs during development of the nervous system and in the adult, the underlying mechanisms are unknown. Here we show that nitric oxide (NO) can induce death of C17.2 NPC by a mechanism requiring activation of p38 MAP kinase, poly(ADP-ribose) polymerase, and caspase-3. Nitric oxide causes release of cytochrome c from mitochondria, and Bcl-2 protects the neural progenitor cells against nitric oxide-induced death, consistent with a pivotal role for mitochondrial changes in controlling the cell death process. Inhibition of p38 MAP kinase by SB203580 abolished NO-induced cell death, cytochrome c release, and activation of caspase-3, indicating that p38 activation serves as an upstream mediator in the cell death process. The anti-apoptotic protein Bcl-2 protected NPC against nitric oxide-induced apoptosis and suppressed activation of p38 MAP kinase. The ability of nitric oxide to trigger death of NPC by a mechanism involving p38 MAP kinase suggests that this diffusible gas may regulate NPC fate in physiological and pathological settings in which NO is produced.

Pediatric caustic ingestion: 50 consecutive cases and a review of the literature

Caustic injury to the aerodigestive tract remains a significant medical and social concern despite various efforts to minimize hazards of caustic household products. Agents with a pH less than two or greater than 12 are extremely corrosive, causing damage that can range from mild to extensive, including esophageal perforation leading to mediastinitis and death at the extreme scale. Methods include retrospective case note review of all admissions to the otolaryngology unit with caustic injury that underwent esophagoscopy to the Children's Hospital Westmead between 1990 and 2007. A protocol-based management system with antibiotics and steroids together with esophagoscopy at 48 hours was implemented. A total of 50 admissions were identified with an average follow-up of 5 years. There were a total of 28 males and 22 females with a median age of 22 months. Forty-nine cases (98%) were accidental. Thirty-eight cases (76%) occurred within the interiors of the family home with the kitchen being the common location. Another seven (14%) occurred within the external environment of the home, usually in the garage or pool shed. The causative agents were varied with 37 (74%) being alkali, three cases (6%) being acidic, and other agents, such as chlorine bleach, being the remainder. The most frequently ingested alkalis were dishwashing powder and disinfectants closely followed by degreasers. Twenty-five children (50%) drank directly from a container with the remainder ingesting granules or powder directly. At esophagoscopy, 17 cases (34%) had grade 1 injury and 10 (20%) had grade 2 injury. Fifty percent of patients of grade 2 injury subsequently developed strictures requiring multiple dilatations. Importantly, six cases (12%) had evidence of esophageal injury without oral injury. Caustic injuries continue to be a significant morbidity in the pediatric patient group. Most cases are still happening as a result of accidental ingestion from unmarked containers within reach of children at home. Oral injury is not always a useful marker of more significant distal injury. A protocol-based management can identify children at risk for long-term stricture earlier.

A simple mechanical mixer for small viscous lipid-containing samples

The construction and performance characteristics of a simple device for rapid and convenient hydration and mixing of small volumes (10-500 microliters) of viscous hydrated lipid samples for use in X-ray diffraction/scattering and other applications are described. The mixer has been used successfully over the past several years in studies of the equilibrium properties of lipid mesophases and of the kinetics and mechanism of phase transitions. It is a low dead-volume (3.6-11.2 microliters) device that was built to facilitate maximal transfer of homogeneously hydrated lipid from the mixer into 1 mm diameter X-ray capillaries with minimal loss of water during transfer and sample manipulation. The device consists of inexpensive, commercially available parts, the most important of which are two microsyringes joined by a small-bore coupling needle. Also described in this report is a technique for determining the water content of the small volume, hydrated samples prepared with the mixer and an accessory for conveniently heating and/or degassing samples during mixing. Inadvertent sample heating that occurs during mixing is described.

The amino terminus of JAK3 is necessary and sufficient for binding to the common gamma chain and confers the ability to transmit interleukin 2-mediated signals

JAK3 is a protein tyrosine kinase that specifically associates with the common gamma chain (gammac), a shared subunit of receptors for interleukin (IL) 2, 4, 7, 9, and 15. Patients deficient in either JAK3 or gammac presented with virtually identical forms of severe combined immunodeficiency (SCID), underscoring the importance of the JAK3-gammac interaction. Despite the key roles of JAK3 and gammac in lymphocytic development and function, the molecular basis of this interaction remains poorly understood. In this study, we have characterized the regions of JAK3 involved in gammac association. By developing a number of chimeric JAK3-JAK2 constructs, we show that the binding specificity to gammac can be conferred to JAK2 by transferring the N-terminal domains of JAK3. Moreover, those JAK3-JAK2 chimeras capable of binding gammac were also capable of reconstituting IL-2 signaling as measured by inducible phosphorylation of the chimeric JAK3-JAK2 protein, JAK1, the IL-2 receptor beta chain, and signal transducer and activator of transcription 5A. Subsequent deletion analyses of JAK3 have identified the N-terminal JH7-6 domains as a minimal region sufficient for gammac association. Furthermore, expression of the mutant containing only the JH7-6 domains effectively competed with full-length JAK3 for binding to gammac. We conclude that the JH7-6 domains of JAK3 are necessary and sufficient for gammac association. These studies offer clues toward a broader understanding of JAK-mediated cytokine signaling and may provide a target for the development of novel therapeutic modalities in immunologically mediated diseases.

Imaging of small-scale features on 433 Eros from NEAR: evidence for a complex regolith

On 25 October 2000, the Near Earth Asteroid Rendevous (NEAR)-Shoemaker spacecraft executed a low-altitude flyover of asteroid 433 Eros, making it possible to image the surface at a resolution of about 1 meter per pixel. The images reveal an evolved surface distinguished by an abundance of ejecta blocks, a dearth of small craters, and smooth material infilling some topographic lows. The subdued appearance of craters of different diameters and the variety of blocks and different degrees of their burial suggest that ejecta from several impact events blanketed the region imaged at closest approach and led to the building up of a substantial and complex regolith consisting of fine materials and abundant meter-sized blocks.

Sperm-egg recognition in the mouse: characterization of sp56, a sperm protein having specific affinity for ZP3

Recognition between mammalian gametes occurs when the plasma membrane of the sperm head binds to the zona pellucida (ZP), an extracellular coat surrounding eggs. ZP3, one of three glycoproteins in the ZP, is the egg protein recognized by sperm. A mouse sperm surface protein, sp56 (M(r) = 56,000), has been identified on the basis of its specific affinity for ZP3 (Bleil, J. D., and P. M. Wassarman. 1990. Proc. Natl. Acad. Sci. USA. 87:5563-5567). Studies presented here were designed to characterize mouse sperm sp56 and to further test whether or not this protein specifically recognizes ZP3. sp56 was purified by both ZP3 affinity chromatography and by ion exchange chromatography followed by size-exclusion chromatography. The purified native protein eluted from size-exclusion columns as a homomultimer (M(r) approximately 110,000). Each monomer of the protein contains intramolecular disulfide bonds, consistent with its extracellular location. Immunohistochemical and immunoblotting studies, using monoclonal antibodies, demonstrated that sp56 is a peripheral membrane protein located on the outer surface of the sperm head plasma membrane, precisely where sperm bind ZP3. Results of crosslinking experiments demonstrated that the ZP3 oligosaccharide recognized by sperm has specific affinity for sp56. Collectively, these results suggest that sp56 may be the sperm protein responsible for sperm-egg recognition in the mouse.