Engraftable human neural stem cells respond to developmental cues, replace neurons, and express foreign genes

Stable clones of neural stem cells (NSCs) have been isolated from the human fetal telencephalon. These self-renewing clones give rise to all fundamental neural lineages in vitro. Following transplantation into germinal zones of the newborn mouse brain they participate in aspects of normal development, including migration along established migratory pathways to disseminated central nervous system regions, differentiation into multiple developmentally and regionally appropriate cell types, and nondisruptive interspersion with host progenitors and their progeny. These human NSCs can be genetically engineered and are capable of expressing foreign transgenes in vivo. Supporting their gene therapy potential, secretory products from NSCs can correct a prototypical genetic metabolic defect in neurons and glia in vitro. The human NSCs can also replace specific deficient neuronal populations. Cryopreservable human NSCs may be propagated by both epigenetic and genetic means that are comparably safe and effective. By analogy to rodent NSCs, these observations may allow the development of NSC transplantation for a range of disorders.

Phylogenetic analysis of Cryptosporidium parasites based on the small-subunit rRNA gene locus

Biological data support the hypothesis that there are multiple species in the genus Cryptosporidium, but a recent analysis of the available genetic data suggested that there is insufficient evidence for species differentiation. In order to resolve the controversy in the taxonomy of this parasite genus, we characterized the small-subunit rRNA genes of Cryptosporidium parvum, Cryptosporidium baileyi, Cryptosporidium muris, and Cryptosporidium serpentis and performed a phylogenetic analysis of the genus Cryptosporidium. Our study revealed that the genus Cryptosporidium contains the phylogenetically distinct species C. parvum, C. muris, C. baileyi, and C. serpentis, which is consistent with the biological characteristics and host specificity data. The Cryptosporidium species formed two clades, with C. parvum and C. baileyi belonging to one clade and C. muris and C. serpentis belonging to the other clade. Within C. parvum, human genotype isolates and guinea pig isolates (known as Cryptosporidium wrairi) each differed from bovine genotype isolates by the nucleotide sequence in four regions. A C. muris isolate from cattle was also different from parasites isolated from a rock hyrax and a Bactrian camel. Minor differences were also detected between C. serpentis isolates from snakes and lizards. Based on the genetic information, a species- and strain-specific PCR-restriction fragment length polymorphism diagnostic tool was developed.

Thrombocytopenia caused by the development of antibodies to thrombopoietin

Thrombocytopenia developed in some individuals treated with a recombinant thrombopoietin (TPO), pegylated recombinant human megakaryocyte growth and development factor (PEG-rHuMGDF). Three of the subjects who developed severe thrombocytopenia were analyzed in detail to determine the cause of their thrombocytopenia. Except for easy bruising and heavy menses, none of these subjects had major bleeding episodes; none responded to intravenous immunoglobulin or prednisone. Bone marrow examination revealed a marked reduction in megakaryocytes. All 3 thrombocytopenic subjects had antibody to PEG-rHuMGDF that cross-reacted with endogenous TPO and neutralized its biological activity. All anti-TPO antibodies were immunoglobulin G (IgG), with increased amounts of IgG4; no IgM antibodies to TPO were detected at any time. A quantitative assay for IgG antibody to TPO was developed and showed that the antibody concentration varied inversely with the platelet count. Anti-TPO antibody recognized epitopes located in the first 163 amino acids of TPO and prevented TPO from binding to its receptor. In 2 subjects, endogenous TPO levels were elevated, but the TPO circulated as a biologically inactive immune complex with anti-TPO IgG; the endogenous TPO in these complexes had an apparent molecular weight of 95 000, slightly larger than the full-length recombinant TPO. None of the subjects had atypical HLA or platelet antigens, and the TPO cDNA was normal in both that were sequenced. Treatment of one subject with cyclosporine eliminated the antibody and normalized the platelet count. These data demonstrate a new mechanism for thrombocytopenia in which antibody develops to TPO; because endogenous TPO is produced constitutively, thrombocytopenia ensues.

O2 activation by nonheme iron complexes: A monomeric Fe(III)-Oxo complex derived from O2

Iron species with terminal oxo ligands are implicated as key intermediates in several synthetic and biochemical catalytic cycles. However, there is a dearth of structural information regarding these types of complexes because their instability has precluded isolation under ambient conditions. The isolation and structural characterization of an iron(III) complex with a terminal oxo ligand, derived directly from dioxygen (O2), is reported. A stable structure resulted from placing the oxoiron unit within a synthetic cavity lined with hydrogen-bonding groups. The cavity creates a microenvironment around the iron center that aids in regulating O2 activation and stabilizing the oxoiron unit. These cavities share properties with the active sites of metalloproteins, where function is correlated strongly with site structure.

NWChem: Past, present, and future

Specialized computational chemistry packages have permanently reshaped the landscape of chemical and materials science by providing tools to support and guide experimental efforts and for the prediction of atomistic and electronic properties. In this regard, electronic structure packages have played a special role by using first-principle-driven methodologies to model complex chemical and materials processes. Over the past few decades, the rapid development of computing technologies and the tremendous increase in computational power have offered a unique chance to study complex transformations using sophisticated and predictive many-body techniques that describe correlated behavior of electrons in molecular and condensed phase systems at different levels of theory. In enabling these simulations, novel parallel algorithms have been able to take advantage of computational resources to address the polynomial scaling of electronic structure methods. In this paper, we briefly review the NWChem computational chemistry suite, including its history, design principles, parallel tools, current capabilities, outreach, and outlook.

The tumor autocrine motility factor receptor, gp78, is a ubiquitin protein ligase implicated in degradation from the endoplasmic reticulum

gp78, also known as the tumor autocrine motility factor receptor, is a transmembrane protein whose expression is correlated with tumor metastasis. We establish that gp78 is a RING finger-dependent ubiquitin protein ligase (E3) of the endoplasmic reticulum (ER). Consistent with this, gp78 specifically recruits MmUBC7, a ubiquitin-conjugating enzyme (E2) implicated in ER-associated degradation (ERAD), through a region distinct from the RING finger. gp78 can target itself for proteasomal degradation in a RING finger- and MmUBC7-dependent manner. Importantly, gp78 can also mediate degradation of CD3-delta, a well-characterized ERAD substrate. In contrast, gp78 lacking an intact RING finger or its multiple membrane-spanning domains stabilizes CD3-delta. gp78 has thus been found to be an example of a mammalian cellular E3 intrinsic to the ER, suggesting a potential link between ubiquitylation, ERAD, and metastasis.

Distinct patterns of tissue-specific lipid accumulation during the induction of insulin resistance in mice by high-fat feeding

AIMS/HYPOTHESIS

While it is well known that diet-induced obesity causes insulin resistance, the precise mechanisms underpinning the initiation of insulin resistance are unclear. To determine factors that may cause insulin resistance, we have performed a detailed time-course study in mice fed a high-fat diet (HFD).

METHODS

C57Bl/6 mice were fed chow or an HFD from 3 days to 16 weeks and glucose tolerance and tissue-specific insulin action were determined. Tissue lipid profiles were analysed by mass spectrometry and inflammatory markers were measured in adipose tissue, liver and skeletal muscle.

RESULTS

Glucose intolerance developed within 3 days of the HFD and did not deteriorate further in the period to 12 weeks. Whole-body insulin resistance, measured by hyperinsulinaemic-euglycaemic clamp, was detected after 1 week of HFD and was due to hepatic insulin resistance. Adipose tissue was insulin resistant after 1 week, while skeletal muscle displayed insulin resistance at 3 weeks, coinciding with a defect in glucose disposal. Interestingly, no further deterioration in insulin sensitivity was observed in any tissue after this initial defect. Diacylglycerol content was increased in liver and muscle when insulin resistance first developed, while the onset of insulin resistance in adipose tissue was associated with increases in ceramide and sphingomyelin. Adipose tissue inflammation was only detected at 16 weeks of HFD and did not correlate with the induction of insulin resistance.

CONCLUSIONS/INTERPRETATION

HFD-induced whole-body insulin resistance is initiated by impaired hepatic insulin action and exacerbated by skeletal muscle insulin resistance and is associated with the accumulation of specific bioactive lipid species.

Ketamine-induced antidepressant effects are associated with AMPA receptors-mediated upregulation of mTOR and BDNF in rat hippocampus and prefrontal cortex

Ketamine exerts fast acting, robust, and lasting antidepressant effects in a sub-anesthetic dose, however, the underlying mechanisms are still not fully elucidated. Recent studies have suggested that ketamine's antidepressant effects are probably attributed to the activation of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors. The present study aimed to observe the effects of AMPA receptor modulators on mammalian target of rapamycin (mTOR) and brain-derived neurotrophic factor (BDNF) expression during the procedure of ketamine exerting antidepressant effects. Therefore, we pretreated rats with NBQX, an AMPA receptor antagonist, or CX546, an AMPA receptor agonist, and subsequently observed the immobility time during the forced swimming test (FST) and the hippocampal and prefrontal cortical levels of mTOR and BDNF. The results showed ketamine decreased the immobility time of rats during the FST and increased the hippocampal and prefrontal cortical mTOR and BDNF. NBQX pretreatment significantly increased the immobility time and decreased the levels of mTOR and BDNF when compared with vehicle 1 (DMSO) pretreatment. CX546 pretreatment significantly decreased the immobility time and increased the levels of mTOR and BDNF when compared with vehicle 2 (DMSO+ethanol) pretreatment. Our results suggest ketamine-induced antidepressant effects are associated with AMPA receptors-mediated upregulation of mTOR and BDNF in rat hippocampus and prefrontal cortex.

Role of mitogen-activated protein kinase phosphatase during the cellular response to genotoxic stress. Inhibition of c-Jun N-terminal kinase activity and AP-1-dependent gene activation

Irradiation of mammalian cells with short wavelength ultraviolet light (UVC) evokes a cascade of phosphorylation events leading to altered gene expression. Both the classic mitogen-activated protein (MAP) kinases and the distantly related c-Jun N-terminal kinases (JNK) contribute to the response via phosphorylation of transcription factors including AP-1. These kinases are themselves regulated via reversible phosphorylation, and several recently identified specific MAP kinase phosphatases (MKP) have been implicated in down-regulating MAP kinase-dependent gene expression in response to mitogens. Here, we provide evidence that MKP-1 plays a role in regulating transcriptional activation in response to UVC as well as another genotoxic agent, methyl methanesulfonate (MMS). We further demonstrate that JNK is a likely target for MKP-1. JNK is shown to be activated by UVC and MMS treatment, while MAP kinase activation occurs only with UVC. Like JNK activation, MKP-1 mRNA is induced by both treatments, and elevated MKP-1 expression coincides with a decline in JNK activity. Constitutive expression of MKP-1 in vivo inhibits JNK activity and reduces UVC- and MMS-induced activation of AP-1-dependent reporter genes.

Guillain-Barré syndrome in northern China. The spectrum of neuropathological changes in clinically defined cases

The pathology of the Guillain-Barré syndrome remains controversial, and autopsied cases available for study by contemporary techniques are uncommon. Large numbers of cases clinically diagnosed as Guillain-Barré syndrome occur in northern China. In this study we examined the neuropathological changes in 12 autopsied cases from Hebei Province, China. Eleven died early in the course of their disease. In all cases tissue was specially handled and fixed for electron microscopy and for immunocytochemistry. Three of these 12 cases had typical acute inflammatory demyelinating polyneuropathy (AIDP) with lymphocytic infiltration and macrophage-mediated demyelination, reproducing the pathological picture most often reported in Guillain-Barré syndrome in North America, Europe, and Australia. Six cases had predominantly axonal involvement, characterized by Wallerian-like degeneration of nerve fibres, with only minimal demyelination and with minimal inflammation in five. Three cases, even though paralysed at the time of death, had only very mild changes in the spinal roots and sciatic nerves. Within the group of six predominantly axonal cases, there were important differences both in the severity of the abnormalities and in the classes of fibres involved. Three cases had extensive Wallerian-like degeneration of sensory as well as motor fibres [acute motor-sensory axonal neuropathy (AMSAN)], while in the other three cases the fibre degeneration affected the motor nerve fibres almost exclusively. These latter cases establish a structural basis for the clinical and electrophysiological picture termed the acute motor axonal neuropathy (AMAN) pattern. In both the AMAN and the AMSAN patterns, a prominent feature was the presence of macrophages within the periaxonal space, surrounding or displacing the axon, and surrounded by an intact myelin sheath. These studies show that the early pathological changes in cases clinically diagnosed as the Guillain-Barré syndrome are diverse and not restricted to the well-known pattern of AIDP, and that the predominant pathological patterns may differ in different parts of the world. The differences in pathological findings between acute inflammatory demyelinating polyneuropathy and the axonal patterns are likely to reflect differences in the pathogenetic mechanisms. The periaxonal macrophages in the axonal patterns suggest that an important epitope may be localized to the axolemma or periaxonal space. The mild cases indicate that severe paralysis can occur early in Guillain-Barré syndrome without prominent structural changes along the nerve, suggesting that physiological block or nerve terminal changes may be implicated.

Highly efficient Heck reactions of aryl bromides with n-butyl acrylate mediated by a palladium/phosphine-imidazolium salt system

[reaction: see text] A new phosphine-imidazolium salt, L.HBr (1, L = (1-ethylenediphenylphosphino-3-(mesityl))imidazol-2-ylidene), has been prepared. A combination of 0.5 mol % of Pd(dba)(2) and 0.5 mol % of L.HBr in the presence of 2 equiv of Cs(2)CO(3) as base has proven to be highly efficient in the Heck coupling reactions of aryl bromides (from electron-deficient to electron-rich aryl bromides) with n-butyl acrylate.

Sodium/hydrogen exchanger gene defect in slow-wave epilepsy mutant mice

The "housekeeping" sodium/hydrogen exchanger, NHE1, mediates the electroneutral 1:1 exchange of Na+ and H+ across the plasma membrane. NHE1 is ubiquitous and is studied extensively for regulation of pHi, cell volume, and response to growth factors. We describe a spontaneous mouse mutant, slow-wave epilepsy, (swe), with a neurological syndrome including ataxia and a unique epilepsy phenotype consisting of 3/sec absence and tonic-clonic seizures. swe was fine-mapped on Chromosome 4 and identified as a null allele of Nhe1. Mutants show selective neuronal death in the cerebellum and brainstem but otherwise are healthy. This first example of a disease-causing mutation in an Nhe gene provides a new tool for studying the delicate balance of neuroexcitability and cell survival within the CNS.

Gate-voltage control of chemical potential and weak antilocalization in Bi₂Se₃

We report that Bi₂Se₃ thin films can be epitaxially grown on SrTiO₃ substrates, which allow for very large tunablity in carrier density with a back gate. The observed low field magnetoconductivity due to weak antilocalization (WAL) has a very weak gate-voltage dependence unless the electron density is reduced to very low values. Such a transition in WAL is correlated with unusual changes in longitudinal and Hall resistivities. Our results suggest a much suppressed bulk conductivity at large negative gate voltages and a possible role of surface states in the WAL phenomena.

Event-related potential indices of semantic priming using masked and unmasked words: evidence that the N400 does not reflect a post-lexical process

Several authors have contended that the N400 is a reflection of a post-lexical event such as that proposed by Neely and Keefe [J.H. Neely, D.E. Keefe, Semantic context effects on visual word processing: a hybrid prospective/retrospective processing theory, in: G.H. Bower (Ed.), The Psychology of Learning and Motivation: Advances in Research and Theory, Vol. 23, Academic Press, New York, 1989, pp. 207-248.], whereby the subject compares the word on the current trial to the "context" provided by the word on the preceding trial [M. Besson, M. Kutas, The many facets of repetition: A cued-recall and event-related potential analysis of repeating words in same versus different sentence contexts, Journal of Experimental Psychology: Learning, Memory and Cognition, 19 (5) (1993), 1115-1133; C. Brown, P. Hagoort, The processing nature of the N400: Evidence from masked priming. Journal of Cognitive Neuroscience, 5(1) (1993), 34-44; P.J. Holcomb, Semantic priming and stimulus degradation: Implications for the role of the N400 in language processing, Psychophysiology 30 (1993), 47-61; M.D. Rugg, M.C. Doyle, Event-related potentials and stimulus repetition in indirect and direct tests of memory, in: H. Heinze, T. Munte, G.R. Mangun (Eds), Cognitive Electrophysiology, Birkhauser Boston, Cambridge, MA, 1994]. A study which used masked primes to directly test this possibility has been reported by Brown and Hagoort [C. Brown, P. Hagoort, The processing nature of the N400: evidence from masked priming. Journal of Cognitive Neuroscience, 5(1) (1993), 34-44]. When the primes were masked, no priming effect was observed on the N400. When behavioral data were collected in the same paradigm, from another group of subjects, the usual priming effect on RT was obtained. Considered together, the data from the two groups of subjects indicated that activation of semantic representations had occurred without conscious awareness. As no N400 priming effect was observed, it was suggested that N400 must reflect a post-lexical process. This interpretation, however, is at odds with the findings of other studies which have reported N400 priming effects under conditions where post-lexical processes would not be thought to operate[J. Anderson, P. Holcomb, Auditory and visual semantic priming using different stimulus onset asynchronies: an event-related brain potential study. Psychophysiology 32 (1995), 177-190; J. Boddy, Event-related potentials in chronometric analysis of primed word recognition with different stimulus onset asynchronies, Psychophysiology 23 (1986), 232-245; D. Deacon, T. Uhm, W. Ritter, S. Hewitt, The lifetime of automatic priming effects may exceed two seconds, Cognitive Brain Research 7 (1999), 465-472; P.J. Holcomb, Automatic and attentional process: an event-related brain potential analysis of semantic priming. Brain and Language 35 (1998) 66-85]. The present study replicated Brown and Hagoort using a repeated measures design, a shorter SOA (stimulus onset asynchrony), and a slightly different threshold setting procedure. Significant priming effects were obtained on the mean amplitude of the N400 regardless of whether the words were masked or unmasked. The findings imply that the processing subserving the N400 is not postlexical, since the N400 was manipulated without the subjects being aware of the identity of the words.

ARF6 targets recycling vesicles to the plasma membrane: insights from an ultrastructural investigation

We have shown previously that the ADP-ribosylation factor (ARF)-6 GTPase localizes to the plasma membrane and intracellular endosomal compartments. Expression of ARF6 mutants perturbs endosomal trafficking and the morphology of the peripheral membrane system. However, another study on the distribution of ARF6 in subcellular fractions of Chinese hamster ovary (CHO) cells suggested that ARF6 did not localize to endosomes labeled after 10 min of horseradish peroxidase (HRP) uptake, but instead was uniquely localized to the plasma membrane, and that its reported endosomal localization may have been a result of overexpression. Here we demonstrate that at the lowest detectable levels of protein expression by cryoimmunogold electron microscopy, ARF6 localized predominantly to an intracellular compartment at the pericentriolar region of the cell. The ARF6-labeled vesicles were partially accessible to HRP only on prolonged exposure to the endocytic tracer but did not localize to early endocytic structures that labeled with HRP shortly after uptake. Furthermore, we have shown that the ARF6-containing intracellular compartment partially colocalized with transferrin receptors and cellubrevin and morphologically resembled the recycling endocytic compartment previously described in CHO cells. HRP labeling in cells expressing ARF6(Q67L), a GTP-bound mutant of ARF6, was restricted to small peripheral vesicles, whereas the mutant protein was enriched on plasma membrane invaginations. On the other hand, expression of ARF6(T27N), a mutant of ARF6 defective in GDP binding, resulted in an accumulation of perinuclear ARF6-positive vesicles that partially colocalized with HRP on prolonged exposure to the tracer. Taken together, our findings suggest that ARF activation is required for the targeted delivery of ARF6-positive, recycling endosomal vesicles to the plasma membrane.

Identification of a chloride-formate exchanger expressed on the brush border membrane of renal proximal tubule cells

A key function of the proximal tubule is retrieval of most of the vast quantities of NaCl and water filtered by the kidney. Physiological studies using brush border vesicles and perfused tubules have indicated that a major fraction of Cl(-) reabsorption across the apical membrane of proximal tubule cells occurs via Cl(-)-formate exchange. The molecular identity of the transporter responsible for renal brush border Cl(-)-formate exchange has yet to be elucidated. As a strategy to identify one or more anion exchangers responsible for mediating Cl(-) reabsorption in the proximal tubule, we screened the expressed sequence tag database for homologs of pendrin, a transporter previously shown to mediate Cl(-)-formate exchange. We now report the cDNA cloning of CFEX, a mouse pendrin homolog with expression in the kidney by Northern analysis. Sequence analysis indicated that CFEX very likely represents the mouse ortholog of human SLC26A6. Immunolocalization studies detected expression of CFEX, but not pendrin, on the brush border membrane of proximal tubule cells. Functional expression studies in Xenopus oocytes demonstrated that CFEX mediates Cl(-)-formate exchange. Taken together, these observations identify CFEX as a prime candidate to mediate Cl(-)-formate exchange in the proximal tubule and thereby to contribute importantly to renal NaCl reabsorption. Given its wide tissue distribution, CFEX also may contribute to transcellular Cl(-) transport in additional epithelia such as the pancreas and contribute to transmembrane Cl(-) transport in nonepithelial tissues such as the heart.

Body distribution of camptothecin solid lipid nanoparticles after oral administration

PURPOSE

The aim of this study was to investigate the specific changes in body distribution of camptothecin (CA) through incorporation into solid lipid nanoparticles (SLN) by peroral route.

METHODS

Camptothecin loaded solid lipid nanoparticles (CA-SLN) coated with poloxamer 188 were produced by high pressure homogenization. The CA-SLN were characterized by transmission electron microscopy and electrophoretic mobility measurement. In vitro release characteristics of camptothecin from CA-SLN were studied at different pH media. The concentration of camptothecin in organs was determined using reversed-phase high-performance liquid chromatography with a fluorescence detector after oral administration of CA-SLN and a camptothecin control solution (CA-SOL).

RESULTS

Our results showed that CA-SLN had an average diameter 196.8 nm with Zeta potential of -69.3 mV. The encapsulation efficiency of camptothecin was 99.6%, and in vitro drug release was achieved up to a week. There were two peaks in the camptothecin concentration-time curves in plasma and tested organs after oral administration of CA-SLN. The first peak was the result of free drug and the second peak was indicative of gut uptake of CA-SLN after 3 hours. In tested organs, the area under curve (AUC) and mean residence time (MRT) of CA-SLN increased significantly as compared with CA-SOL, and the increase of brain AUC was the highest among all tested organs.

CONCLUSIONS

The results indicate SLN could be a promising sustained release and targeting system for camptothecin or other lipophilic antitumor drugs after oral administration.

Pti4 is induced by ethylene and salicylic acid, and its product is phosphorylated by the Pto kinase

The tomato Pti4 gene encodes a transcription factor that was identified on the basis of its specific interaction with the product of the Pto disease resistance gene in a yeast two-hybrid system. We show here that the Pti4 protein specifically binds the GCC-box cis element, which is present in the promoter region of many pathogenesis-related (PR) genes. Expression of the Pti4 gene in tomato leaves was rapidly induced by ethylene and by infection with Pseudomonas syringae pv tomato, and this induction preceded expression of GCC-box-containing PR genes. Although salicylic acid also induced Pti4 gene expression, it did not induce GCC-box PR genes. Rather, salicylic acid antagonized ethylene-mediated expression of GCC-box PR genes. We demonstrate that the Pti4 protein is specifically phosphorylated by the Pto kinase and that this phosphorylation enhances binding of Pti4 to the GCC box. In addition, induced overexpression of Pto and Pti4 in tomato leaves resulted in a concomitant increase in GCC-box PR genes. Our results support a model in which phosphorylation of the Pti4 protein by the Pto kinase enhances the ability of Pti4 to activate expression of GCC-box PR genes in tomato.

Chemical composition, crystal size and lattice structural changes after incorporation of strontium into biomimetic apatite

Recently, strontium (Sr) as ranelate compound has become increasingly popular in the treatment of osteoporosis. However, the lattice structure of bone crystal after Sr incorporation is yet to be extensively reported. In this study, we synthesized strontium-substituted hydroxyapatite (Sr-HA) with different Sr content (0.3%, 1.5% and 15% Sr-HA in mole ratio) to simulate bone crystals incorporated with Sr. The changes in chemical composition and lattice structure of apetite after synthetic incorporation of Sr were evaluated to gain insight into bone crystal changes after incorporation of Sr. X-ray diffraction (XRD) patterns revealed that 0.3% and 1.5% Sr-HA exhibited single phase spectrum, which was similar to that of HA. However, 15% Sr-HA induced the incorporation of HPO4(2-) and more CO3(2-), the crystallinity reduced dramatically. Transmission electron microscopy (TEM) images showed that the crystal length and width of 0.3% and 1.5% Sr-HA increased slightly. Meanwhile, the length and width distribution were broadened and the aspect ratio decreased from 10.68+/-4.00 to 7.28+/-2.80. The crystal size and crystallinity of 15% Sr-HA dropped rapidly, which may suggest that the fundamental crystal structure is changed. The findings from this work indicate that current clinical dosage which usually results in Sr incorporation of below 1.5% may not change chemical composition and lattice structure of bone, while it will broaden the bone crystal size distribution and strengthen the bone.

Lysophosphatidic acid-induced neurite retraction in PC12 cells: control by phosphoinositide-Ca2+ signaling and Rho

The endogenous phospholipid mediator lysophosphatidic acid (LPA) caused growth cone collapse, neurite retraction, and cell flattening in differentiated PC12 cells. Neurite retraction was blocked by cytochalasin B and ADP-ribosylation of the small-molecular-weight G protein Rho by the Clostridium botulinum C-3 toxin. LPA induced a transient rise in the level of inositol 1,4,5-trisphosphate, and retraction was blocked by inhibitors of phospholipase beta. Repeated application of LPA elicited homologous desensitization of the Ca2+ mobilization response. The activation of the phosphoinositide (PIP)-Ca2+ second messenger system played a permissive role in the morphoregulatory response. Blockers of protein kinase C--chelerythrine, a myristoylated pseudosubstrate peptide, staurosporine, and depletion of protein kinase C from the cells by long-term phorbol ester treatment--all diminished neurite retraction by interfering with LPA-induced Ca2+ mobilization, which was required for the withdrawal of neurites. A brief 15-min treatment with 4 beta-phorbol 12-myristate 13-acetate also blocked retraction and Ca2+ mobilization, by inactivating the LPA receptor. Inhibition of protein tyrosine phosphorylation by herbimycin diminished retraction. Although activation of the PIP-Ca2+ second messenger system appears necessary for the Rho-mediated rearrangements of the actin cytoskeleton, bradykinin, which activates similar signaling events, failed to cause retraction, indicating that a yet unidentified novel mechanism is also involved in the LPA-induced morphoregulatory response.

A role for CREB binding protein and p300 transcriptional coactivators in Ets-1 transactivation functions

The Ets-1 transcription factor plays a critical role in cell growth and development, but the means by which it activates transcription are still unclear (J. C. Bories, D. M. Willerford, D. Grevin, L. Davidson, A. Camus, P. Martin, D. Stehelin, F. W. Alt, and J. C. Borles, Nature 377:635-638, 1995; N. Muthusamy, K. Barton, and J. M. Leiden, Nature 377:639-642, 1995). Here we show that Ets-1 binds the transcriptional coactivators CREB binding protein (CBP) and the related p300 protein (together referred to as CBP/p300) and that this interaction is required for specific Ets-1 transactivation functions. The Ets-1- and c-Myb-dependent aminopeptidase N (CD13/APN) promoter and an Ets-1-dependent artificial promoter were repressed by adenovirus E1A, a CBP/p300-specific inhibitor. Furthermore, Ets-1 activity was potentiated by CBP and p300 overexpression. The transactivation function of Ets-1 correlated with its ability to bind an N-terminal cysteine- and histidine-rich region spanning CBP residues 313 to 452. Ets-1 also bound a second cysteine- and histidine-rich region of CBP, between residues 1449 and 1892. Both Ets-1 and CBP/p300 formed a stable immunoprecipitable nuclear complex, independent of DNA binding. This Ets-1-CBP/p300 immunocomplex possessed histone acetyltransferase activity, consistent with previous findings that CBP/p300 is associated with such enzyme activity. Our results indicate that CBP/p300 may mediate antagonistic and synergistic interactions between Ets-1 and other transcription factors that use CBP/p300 as a coactivator, including c-Myb and AP-1.

Segregation of human neural stem cells in the developing primate forebrain

Many central nervous system regions at all stages of life contain neural stem cells (NSCs). We explored how these disparate NSC pools might emerge. A traceable clone of human NSCs was implanted intraventricularly to allow its integration into cerebral germinal zones of Old World monkey fetuses. The NSCs distributed into two subpopulations: One contributed to corticogenesis by migrating along radial glia to temporally appropriate layers of the cortical plate and differentiating into lamina-appropriate neurons or glia; the other remained undifferentiated and contributed to a secondary germinal zone (the subventricular zone) with occasional members interspersed throughout brain parenchyma. An early neurogenetic program allocates the progeny of NSCs either immediately for organogenesis or to undifferentiated pools for later use in the "postdevelopmental" brain.

Crystal structure of human mitochondrial single-stranded DNA binding protein at 2.4 A resolution

We solved the crystal structure of the homotetrameric single-stranded DNA binding (SSB) protein from human mitochondria at a resolution of 2.4 A. The tetramer is formed by two dimers interacting head-to-head and shows D2 symmetry. Sequence-related tetrameric SSB proteins occur in prokaryotes and eukaryotic mitochondria; this is the first report of an atomic resolution structure of this type of protein. Using biochemical data and analysis of sequence homologies, we were able to correlate the functional properties with structure. We propose that ssDNA wraps around the tetrameric HsmtSSB protein through electropositive channels guided by flexible loops.

Dynamic positioning of mitotic spindles in yeast: role of microtubule motors and cortical determinants

In the budding yeast Saccharomyces cerevisiae, movement of the mitotic spindle to a predetermined cleavage plane at the bud neck is essential for partitioning chromosomes into the mother and daughter cells. Astral microtubule dynamics are critical to the mechanism that ensures nuclear migration to the bud neck. The nucleus moves in the opposite direction of astral microtubule growth in the mother cell, apparently being "pushed" by microtubule contacts at the cortex. In contrast, microtubules growing toward the neck and within the bud promote nuclear movement in the same direction of microtubule growth, thus "pulling" the nucleus toward the bud neck. Failure of "pulling" is evident in cells lacking Bud6p, Bni1p, Kar9p, or the kinesin homolog, Kip3p. As a consequence, there is a loss of asymmetry in spindle pole body segregation into the bud. The cytoplasmic motor protein, dynein, is not required for nuclear movement to the neck; rather, it has been postulated to contribute to spindle elongation through the neck. In the absence of KAR9, dynein-dependent spindle oscillations are evident before anaphase onset, as are postanaphase dynein-dependent pulling forces that exceed the velocity of wild-type spindle elongation threefold. In addition, dynein-mediated forces on astral microtubules are sufficient to segregate a 2N chromosome set through the neck in the absence of spindle elongation, but cytoplasmic kinesins are not. These observations support a model in which spindle polarity determinants (BUD6, BNI1, KAR9) and cytoplasmic kinesin (KIP3) provide directional cues for spindle orientation to the bud while restraining the spindle to the neck. Cytoplasmic dynein is attenuated by these spindle polarity determinants and kinesin until anaphase onset, when dynein directs spindle elongation to distal points in the mother and bud.