Head-direction cells in the rat posterior cortex. II. Contributions of visual and ideothetic information to the directional firing

This study investigated the effects of visual and ideothetic cues on the spatial tuning of head-direction (HD) cells recorded in the rat posterior cortices. Extracellular, single unit responses were recorded from animals performing each of two different tasks, a spatial working memory task on a radial-arm maze and a passive rotation task on a modified "lazy Susan" platform. The influence of visual cues was assessed by manipulating the position of one white and three black cue-cards placed around the maze. We found three major categories of HD cells based on their response to cue manipulations in the maze tasks. Type A cells (10/41) rotated their preferred directions along with the rotation of the cues. The majority (type B, 25/41) of the HD cells were unaffected by the rotation of visual cues, maintaining their established preferred direction. Type C cells (6/41) showed complex responses to cue rotation, with the preferred direction reflecting either a combination of both type A and type B responses or an unpredictable response. The results indicate that the internal representation of directionality can be calibrated by visual cues and that some mnemonic processes may have been involved in the registration of the previous cue locations. Eleven cells were tested in both the maze task and the passive rotation task. Most (9/11) showed a significant directionality in the former task, but showed either no or weak directionality in the latter task, suggesting that movement-related ideothetic cues may be used in supporting the directional firing of these cells. Only two cells showed significant directionality in both tasks. Their established preferred directions did not rotate along with the cues in the maze task, but did rotate with the cues in the passive rotation task. We conclude that the dynamic aspect of the directional tuning in these cortical HD cells may represent on-line calibration of an angular coordinate representation.

[Pharmacological actions of hyphae body of Auricularia auricula (L. ex Hook) Underw and its alcoholic extract]

The percent peripheral blood T lymphocytes were elevated and HC50 reduction induced by cyclophosphamide was recovered after the hyphae body of Auricularia auricula had been ip administered in mice. The action of blood platelet agglutination in rats induced by ADP was inhibited and the time of erythrocytic electrophoresis in mice was shortened after the alcoholic extract had been ig administered.

An accurate impression method for implant prosthesis fabrication

The long-term success of an implant prosthesis depends not only on the development of osseointegration, but also on the maintenance of osseointegration after the prosthetic phase. To achieve this, a passive superstructure must be fabricated. Errors that result from the impression transfer method of implant position during the impression procedures often made it necessary to section and solder metal frameworks repeatedly. This article presents a modified impression technique intended to deal with the problems of more traditional impressions with the aim of achieving a more accurate master cast.

Phospholipid metabolite expression by head and neck squamous cell carcinoma

OBJECTIVE

To characterize the presence and production of various phospholipid metabolites by head and neck squamous cell carcinoma (HNSCC) and squamous cell carcinoma cell lines in vitro and in vivo.

DESIGN

The HNSCC tumor homogenates and supernatants of HNSCC tumor cultures and established squamous cell carcinoma cell lines were assayed for prostaglandin E2 (PGE2), leukotriene B4 (LTB4), and platelet activating factor (PAF). In vitro experiments were carried out under baseline conditions or with exposure to several known immunomodulators (epidermal growth factor, bacterial lipopolysaccharide, and interleukin 1).

PATIENTS

The HNSCC tumor tissue was obtained from primary tumor or cervical lymph node metastasis of surgical resections.

MAIN OUTCOME MEASURES

Prostaglandin E2, LTB4, and PAF were measured in tumor homogenates and cell culture supernatants using standardized radioimmunoassay kits.

RESULTS

All tumor homogenates (eight of eight) contained detectable levels of PGE2 (range, 324 to 2258 pg/g of tumor tissue) and LTB4 (range, 790 to 41,900 pg/g of tumor tissue); PAF was detected in six of eight homogenates (range, 7362 to 40,788 pg/g of tumor tissue). All of the short-term primary HNSCC tumor cultures and squamous carcinoma lines produced PGE2 (range, 90 to 1160 pg/10(6) cells), and half of the cultures produced LTB4 (range, 100 to 1700 pg/10(6) cells); none of the cultures or cell lines produced detectable levels of PAF. Interleukin 1 significantly enhanced production of PGE2 by tumor cultures (P < .02). Characterization of tumor cultures with a fibroblast antibody marker, BR2, revealed that 26% to 64% of tumor culture cells were fibroblasts.

CONCLUSIONS

Prostaglandin E2, LTB4, and PAF are present in the tumor microenvironment, where they may be involved in the local immunosuppression phenomenon seen in HNSCC. Both PGE2 and LTB4 were produced in vitro by tumor cultures and squamous cell carcinoma cell lines; PAF was not produced by tumor cultures in vitro and therefore may be a product of local immune cells in HNSCC in vivo. Interleukin 1 and PGE2 may interact in immunoregulation in the HNSCC tumor microenvironment.

Survival of Psychrotrophic Vibrio mimicus , Vibrio fluvialis and Vibrio parahaemolyticus in Culture Broth at Low Temperatures

Pathogenic vibrios are important etiologic agents in tropical regions and have been frequently recovered from seafoods and aquacultured foods. A number of psychrotrophic vibrios were isolated and selected from frozen seafoods and their survivals in tryptic soy broth (TSB) at 4°C and -30°C were studied. These psychrotrophic strains showed good survival at low temperatures and could probably enhance the risk of vibrios in frozen foods. Vibrio mimicus 70 and 198, Vibrio fluvialis 52 and Vibrio parahaemolyticus 205 survived well at 10°C, 4°C and -30°C, while the non-cold fitter V. fluvialis 28 was completely inactivated in the test periods. These strains were not heat resistant and could be easily inactivated by heat treatment. Effect of phosphates may be different for. various Vibrio species at low temperatures. Survival of V. parahaemolyticus 205 was significantly protected by the heated metaphosphate at 4°C by lowering the lethality of cold injured cells but not by increasing the level of uninjured viable cells. Pyrophosphate was inhibitory to this V. parahaemolyticus strain at -30°C.

[Studies on the isolation of endogenous sleep factors from Tupaia Belangeri Chinensis (TBC) after sleep deprivation]

The present study was undertaken to explore endogenous sleep factors isolated from 48-72 h sleep deprived (SD) male Tupaia belangeri chinensis (TBC). Only drink ad libitum (10% glucose) was available within 24 h before collection of urine. Controlled "clean" urinary samples were pooled and stored at 20 C. Fraction I-V from the urine were determined after ultrafiltration and Sephadex-G15. Amino-acid analysis of each fraction was automatically done by a 835 Amino-acid Analyzer, respectively. Bioassay was performed in 40 adult rabbits weighing 2.5-3.5 kg of either sex. Experiments were undertaken via the mesodiencephalic intraventricular infusion. Results show that S2C (Fraction-III) (50 micrograms/rabbit, i.c.v.) exhibited significant delta-enhancing effect compared to the controls. Further purification was done with Sephadex G-25 and Sephadex LH-20. The more purified S4B (50 micrograms/rabbit, i.c.v.) also exhibited significant delta-enhancing effect compared to the controls. The amino-acid analysis of Fraction-III revealed that the compositional contents of S2C and S4B are different from what have been known with Factor S, DSIP and SPS.

Tat-mediated delivery of heterologous proteins into cells

The Tat protein of human immunodeficiency virus 1 (HIV-1) can enter cells efficiently when added exogenously in tissue culture. To assess if Tat can carry other molecules into cells, we chemically cross-linked Tat peptides (residues 1-72 or 37-72) to beta-galactosidase, horseradish peroxidase, RNase A, and domain III of Pseudomonas exotoxin A (PE) and monitored uptake colorimetrically or by cytotoxicity. The Tat chimeras were effective on all cell types tested, with staining showing uptake into all cells in each experiment. In mice, treatment with Tat-beta-galactosidase chimeras resulted in delivery to several tissues, with high levels in heart, liver, and spleen, low-to-moderate levels in lung and skeletal muscle, and little or no activity in kidney and brain. The primary target within these tissues was the cells surrounding the blood vessels, suggesting endothelial cells, Kupffer cells, and/or splenic macrophages. Tat-mediated uptake may allow the therapeutic delivery of macromolecules previously thought to be impermeable to living cells.

A sequence-specific single-stranded DNA-binding protein that is responsive to epidermal growth factor recognizes an S1 nuclease-sensitive region in the epidermal growth factor receptor promoter

An epidermal growth factor (EGF) responsive DNA-binding protein (ERDBP-1) has been identified. It recognizes with high affinity and specificity a specific single-stranded DNA sequence located in the S1 nuclease-sensitive site of the EGF receptor (EGFR) 5' flanking region. The EGF-responsive element, determined by footprint analysis, is located from -364 to -344 (86-106 base pairs upstream from the major in vivo transcription initiation site). The factor does not recognize the antisense DNA sequence or double-stranded DNA of the EGF-responsive element. Three bands were observed by mobility shift assay using nuclear extracts from normal human keratinocytes. UV cross-linking followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed one major band with molecular weight in the range of 121,000 to 128,000. The induction of ERDBP-1 became evident 3 to 4 h after EGF stimulation and remained elevated as long as EGF was present. HL60 cells are devoid of endogenous EGFR and produce no ERDBP-1. Retroviral gene transfer of EGFR into HL60 cells resulted in induction of ERDBP-1 by EGF to levels comparable to those found in human keratinocytes.

Retroviral gene transfer of epidermal growth factor receptor into HL60 cells results in a partial block of retinoic acid-induced granulocytic differentiation

HL60 cells are devoid of endogenous epidermal growth factor receptor (EGFR). They respond to retinoic acid and undergo terminal granulocytic differentiation. EGFR complementary DNA was introduced into HL60 cells by retroviral gene transfer. Scatchard plot showed that the binding characteristics are identical to those of A431 cells. HL60-EGFR cells were estimated to express 34,000 EGFR/cell (Kd = 5 nM). The tyrosine phosphorylation upon ligand binding is the first step of signal transduction. The dominant phosphotyrosyl proteins in epidermal growth factor-stimulated HL60-EGFR cells include a 170 kDa protein (EGFR itself), and 125 and 53 kDa proteins. The EGFR signal results in the induction of 92 kDa gelatinase/matrix metalloproteinase in HL60-EGFR cells, thereby providing evidence of the function of the exogenous EGFR and a semiquantitative measure of the EGFR signal. These HL60-EGFR cells offer a unique opportunity to examine the potentially important role of EGFR (c-erbB) in maintaining homeostasis between self-renewal and differentiation. c-erbB has been shown to play a physiological role in the self-renewal of the very early avian stem cells which do express EGFR. The v-erbB (double truncated EGFR) has been shown to cause avian erythroblastosis. We found that these HL60-EGFR cells responded to retinoic acid differently from the HL60-control cells. A partial block of only 45% granulocytic differentiation and concomitant proliferation was noted, consistent with a shift of balance between self-renewal and differentiation toward the former.

Pentose phosphate pathway alterations in multi-drug resistant leukemic T-cells: 31P NMR and enzymatic studies

31P NMR studies were carried out on the parental drug-sensitive human T-lymphoblastoid cell line CCRI-CEM (CEM) and its multi-drug-resistant (MDR) CEM-VBL100 variants, to assess the role of the pentose phosphate (PP) in MDR expression. CEM and CEM-VBL100 were incubated in the presence of 2-deoxyglucose, as recently proposed by our group (Clin. Chim. Acta 208: 39, 1992). Accumulation of 2-deoxyglucose 6-phosphate was much lower in the drug-resistant than in sensitive cells, indicating PP shunt activation in the MDR variants. This result was confirmed by enzymatic analyses, which demonstrated that, with respect to the parental line, the MDR variant was characterized by a) unaltered hexokinase activity; b) higher glucose 6-phosphate dehydrogenase activity; c) increased levels of reduced glutathione and marked increase of glutathione peroxidase activity after cell exposure to an oxidizing agent (tert-butylhydroperoxide). These results support the view that cell detoxification mechanisms mediated by the pentose phosphate pathway may contribute to the expression of MDR in tumours.

Altered epidermal growth factor signal transduction in activated Ha-ras-transformed human keratinocytes

Epidermal growth factor (EGF) can stimulate proliferation and 92 kDa gelatinase/matrix metalloproteinase (MMP-9) expression. The induction of MMP-9 is not only pathologically significant for invasion and metastasis, but also serves as a semiquantitative measure of EGF signal transduction. In order to examine the role of mutated ras p21 in EGF signal transduction, an activated Ha-ras-transformed human keratinocyte cell line was developed and characterized. Overexpression of the mutated Ha-ras p21 in these cells was demonstrated. Our results showed that EGF induced 92 kDa MMP-9 secretion was doubled in the ras-transformed keratinocytes in comparison to the parent cells. The karyotype, the expression of EGF receptor (EGFR) and transforming growth factor (TGF) alpha at the mRNA level remained unchanged. These results suggest that the presence of high levels of mutated ras p21 may be responsible for the aberrant EGF signal transduction and contributes to transformation. In addition, a reduction of TGF beta expression at mRNA level by 70% was found in the activated Ha-ras-transformed keratinocytes when compared to the parent cells.

Enflurane inhibits NMDA, AMPA, and kainate-induced currents in Xenopus oocytes expressing mouse and human brain mRNA

Effects of enflurane, an inhalational anesthetic, on NMDA, AMPA, and kainate-gated currents were examined in Xenopus laevis oocytes expressing mouse or human brain mRNA. In oocytes expressing mouse mRNA, enflurane at an anesthetic concentration (1.8 mM) inhibited the NMDA-, AMPA-, and kainate-induced currents by 29-40%, 30-33%, and 20-27%, respectively, suggesting that all three glutamate ionotropic receptors are susceptible to suppression by inhalational anesthetics. Furthermore, inhibition by enflurane was independent of the concentrations of the agonists (NMDA, AMPA, and kainate) or the NMDA-coagonist (glycine). This suggests that enflurane inhibition does not result from a competitive interaction at glutamate or glycine binding sites. Enflurane also suppressed the oscillation and apparent desensitization of NMDA currents, suggesting an inhibition of Ca2+ influx through the NMDA channel. In oocytes expressing human brain mRNA, only kainate produced observable currents. Kainate currents of human channels were smaller in size than those of the mouse; however, the kainate concentration-response curve and percent inhibition (27-29%) by enflurane were similar for mice and humans. The results suggest that human and mouse kainate receptors have similar pharmacological characteristics.

[Efficacy of xiaoxingzhang guttae ophthalmic eye drops in the treatment of experimental herpes simplex keratitis]

The new guttae ophthalmic Xiaoxingzhang (XXZ) was extracted from Radix Actinidiae, a traditional Chinese herbal drug. The 50% inhibition concentration (IC50) of XXZ on type I Herpes Simplex Virus (HSV-1) in virus cell cultures is 165.48-174.73 micrograms/ml. However, XXZ concentrations greater than 400 micrograms/ml did not cause any microscopically visible disruption of vero cells. The efficacy of XXZ in the treatment of experimental Herpes Simplex Keratitis (HSK) in rabbits is higher than that of idoxuridine. The effective doses of XXZ are not toxic to corneal epithelium. The results suggest that XXZ as a new anti-HSV preparation is potentialy useful in the treatment of patients with HSK.

Cytokine expression by head and neck squamous cell carcinomas

Cytokines are known to play an important role in host defense by regulating the function, growth, and differentiation of the cells of the immune system. We hypothesize that, in the tumor microenvironment, tumor cells and resident tissue cells (e.g., fibroblasts) also produce cytokines that may regulate the local immune response to tumors. Initially, homogenates of eight head and neck squamous cell carcinomas (HNSCC) were assayed for the presence of interleukin-1 (IL-1), interleukin-4 (IL-4), interleukin-6 (IL-6), and granulocyte-macrophage colony-stimulating factor (GM-CSF) to establish the presence of these cytokines in the tumors in vivo. We detected IL-1 in all tumor homogenates and IL-4, IL-6, and GM-CSF in some homogenates. To assess the ability of HNSCC to produce these cytokines, supernatants of short-term primary cultures of HNSCC were assayed for the same cytokines. No IL-1 was detected, although baseline levels of IL-4, IL-6, and GM-CSF were present. However, the stimulation of primary tumor cultures with exogenous IL-1 induced or significantly enhanced production of IL-4 (p < 0.01), IL-6 (p < 0.001), and GM-CSF (p < 0.02). These results support our hypothesis that HNSCC secrete cytokines that may influence the response of local immune cells. Our data also suggest that IL-1 may have a central role in regulating the local immune response through the enhancement or induction of cytokine production by tumor and/or resident tissue cells.

General anesthetics potentiate gamma-aminobutyric acid actions on gamma-aminobutyric acidA receptors expressed by Xenopus oocytes: lack of involvement of intracellular calcium

Potentiation of the gamma-aminobutyric acid (GABAA) receptor-gated Cl- channel response has been suggested to be a primary action of some anesthetic agents. We asked whether the GABAA receptor is a target site common for general anesthetics that are chemically and structurally diverse. This hypothesis was tested in Xenopus oocytes expressing mouse cortical mRNA, and GABA-activated Cl- currents were measured using two-electrode voltage clamping. General anesthetics, including inhalational (halothane, diethylether, enflurane and isoflurane), i.v. (3 alpha-hydroxy-5 alpha-dihydroprogesterone, ketamine and propofol) and alcohol (pentanol) anesthetics, enhanced GABA-induced currents by 56 to 1089% at concentrations that were clinically relevant. The results suggest that potentiation of the GABAA receptor/channel response may be a common action for anesthetic agents. Moreover, anesthetic effects were dependent on GABA concentrations; the enhancement was marked with low GABA concentrations and was exponentially decreased as the GABA concentration increased. Also, anesthetic effects were dependent on anesthetic concentrations. The apparent EC50 of halothane was found to be similar to the anesthetic ED50. We also investigated the role of intracellular Ca++ in mediating anesthetic enhancement of the GABA current. We found that intracellular injection of the Ca++ chelator, EGTA, did not change the enhancement by anesthetics. In addition, these anesthetics alone did not produce significant currents, suggesting that the Ca(++)-dependent Cl- current was not activated by these anesthetics per se. Thus, we found that diverse anesthetics potentiate GABA-induced Cl- currents, but this action is not mediated by a release of intracellular Ca++.

Structure/function studies on vascular cell adhesion molecule-1

Vascular cell adhesion molecule-1 (VCAM1) is a member of the immunoglobulin (Ig) superfamily which interacts with the integrin very late antigen-4 (VLA4). The VCAM1/VLA4 interaction mediates both adhesion and signal transduction and is thought to play an important role in inflammatory and immune responses in vivo. The major form of human VCAM1 contains seven extracellular Ig-like domains, with domain 1 designated as the most N-terminal. We have examined the relationship between human VCAM1 structure and function using a combination of domain truncation mutants and proteolytic fragmentation of recombinant soluble VCAM1. We have characterized two regions of VCAM1, localized to domains 4 and 5, which are highly sensitive to proteolytic cleavage, localized the epitope of the blocking monoclonal antibody 4B9 to domain 1, and found that domains 1-3 are sufficient for both its adhesive function and its ability to initiate T cell activation.

Schistosoma mansoni p48 eggshell protein gene: characterization, developmentally regulated expression and comparison to the p14 eggshell protein gene

Egg production by worm pairs is a major cause of pathogenesis in schistosomiasis. To further the understanding of female reproductive development, we have isolated and characterized a complete copy of an eggshell protein precursor gene, p48. Sequence analysis reveals that the gene has 3 open reading frames and does not contain an intron. One of the open reading frames, ORF1, encodes a polypeptide of 50 kDa which shows strong homology to insect chorion proteins. Determination of the position of the mRNA cap-site facilitated identification of putative regulatory elements in the 5' upstream region of the gene. Some of these elements (e.g., TCACGT) have been shown to play a role in the regulation of chorion gene expression in insects. p48 mRNA is detectable only in mature female worms and the ability to detect the mRNA coincides temporally with worm pairing. Quantitative comparisons, during female reproductive development, of p48 transcripts to those from another eggshell protein precursor gene, p14, show that the p48 mRNA is significantly less abundant than p14 mRNA. In mature female worms, p48 mRNA can only be detected in vitelline cells. Antibodies made against the polypeptide sequence deduced from ORF1 of the p48 gene recognize a 50-kDa molecule in extracts from mature female worms, but not in extracts from immature females or males.

Max: functional domains and interaction with c-Myc

The product of the c-myc proto-oncogene is a DNA-binding protein, the deregulated expression of which is associated with a variety of malignant neoplasms. The cDNA for the max gene was recently cloned as a result of the ability of its protein product to interact with the c-Myc protein. We studied bacterially produced Max, c-Myc, and a series of truncated c-Myc proteins. Full-length c-Myc alone cannot bind DNA. However, a truncated c-Myc protein comprising the basic, helix-loop-helix, and leucine zipper regions can bind specifically to DNA bearing the sequence GGGCAC(G/A)TGCCC. Max protein, either alone or in a heteromeric complex with full-length c-Myc, binds to the same core sequence. Using a novel combination of chemical and photo-cross-linking analysis, we demonstrate that either Max or a c-Myc/Max heteromeric complex binds to DNA virtually exclusively in a dimeric structure. Using fusion proteins in cultured cells, we establish a number of functional characteristics of Max. First, we show that Max can interact with c-Myc intracellularly in a manner dependent on the integrity of the helix-loop-helix and leucine zipper motifs. Second, a nuclear localization domain that contains the sequence PQSRKKLR is mapped to the carboxy-terminal region of Max. Third, Max lacks a transcriptional activation domain that is functional in Chinese hamster ovary cells when fused to a heterologous DNA-binding domain. These data suggest that Max may serve as a cofactor for c-Myc in transcriptional activation or, by itself, as a transcriptional repressor.

Identification and characterization of an acyl-CoA:triterpene acyltransferase activity in rabbit and human tissues

Rabbit and human tissues contain substantial amounts of an unusual lipid, a fatty acid ester of a pentacyclic triterpene, that is a potent in vitro inhibitor of acyl-CoA:cholesterol acyltransferase (ACAT). A possible origin of the triterpene ester is via dietary absorption of plant triterpenes (which have a similar structure to the triterpene moiety of the animal triterpene ester), followed by fatty acid esterification of the triterpene in animal tissues. To support this idea, homogenates of rabbit and human enterocytes and liver are now shown to contain an acyl-CoA:triterpene acyltransferase activity (ATAT) which esterifies triterpene to a fatty acid. The enzyme activity was stimulated by exogenous triterpene and required ATP and coenzyme A when fatty acid was used as substrate; ATP and coenzyme A were not required when fatty acyl-CoA was used. ATAT was not inhibited by two structurally different ACAT inhibitors, which may indicate that ACAT and ATAT are different enzymes. Rat enterocytes and liver contained very little ATAT activity, consistent with the finding that rat liver contained very little triterpene ester. To establish that triterpene esterification occurs in vivo, [3H]triterpene was shown to be incorporated into triterpene ester in several organs and tissues from a rabbit given a gastric bolus of the labeled triterpene. These data provide support for the hypothesis that triterpene esters in animal tissues arise from the dietary absorption of triterpenes followed by the esterification of the triterpenes by an enzymatic activity in the animal tissues.

The increased potency of cross-linked lymphocyte function-associated antigen-3 (LFA-3) multimers is a direct consequence of changes in valency

We have used chemically cross-linked dimers, trimers, and tetramers of lymphocyte function-associated antigen-3 (LFA-3) to study the role of multivalency in the interaction of the protein with its receptor, CD2. The cross-linked adducts showed enhanced activity in systems where LFA-3 has been shown to (i) block LFA-3/CD2 interactions in a rosetting assay and (ii) provide through the CD2 on peripheral blood lymphocytes a trigger for T-cell proliferation. The level of increase was directly related to the valency state of the multimers. In the rosetting assay, the dimers, trimers, and tetramers, by weight, exhibited 15-, 150-, and 430-fold increases in activity over monomeric LFA-3. In the proliferation assay, the tetramer produced a 6-fold increase in thymidine incorporation at 0.06 micrograms/ml, the trimer was 100 times less active than the tetramer, and the dimer and monomer were inactive. The LFA-3 multimers were generated using a three-step cross-linking chemistry that was targeted at the carbohydrates on LFA-3. With this procedure over 60% of the starting protein was converted into multimers with no effect on function. The cross-linking approach should be applicable to other surface antigens, providing a simple method for analyzing multivalent interactions.

Production of multimeric forms of CD4 through a sugar-based cross-linking strategy

We have developed a three-step cross-linking procedure that is specifically targeted at the carbohydrate on a protein and applied it to CD4 as a model system for studying the role of multivalent interactions in function. In the first step CD4 was oxidized with periodate, creating aldehydes that served as targets for the subsequent chemistry. Next the aldehydes were modified with cystamine, converting the reactive group into a thiol. Finally cross-linking through the thiol moiety was generated with the homobifunctional cross-linker bismaleimidohexane. With this procedure, approximately 60% of the CD4 was converted into higher molecular weight complexes that were soluble and retained function as assessed by glycoprotein gp120 binding activity. CD4 dimers and tetramers by mass were 4 and 15 times as active as CD4 monomer in blocking virus infection with HTLV-IIIB in an in vitro cellular assay. The cross-linking chemistry provides an efficient method for producing homomultimers of a glycoprotein.

The remodeling of synaptic extracellular matrix and its dynamic relationship with nerve terminals at living frog neuromuscular junctions

The question of whether the synaptic extracellular matrix undergoes remodeling and how this remodeling is related to nerve terminal plasticity was examined in living neuromuscular junctions of adult frogs. Sartorius muscles were double stained with a fluorescent nerve terminal dye 4-(4-diethylamino-styryl)-N-methylpyridinium iodide (4-Di-2-Asp) and rhodamine-tagged peanut agglutinin (PNA) which recognizes synaptic extracellular matrix. Both nerve terminals and synaptic extracellular matrix in 200 identified normal junctions were visualized in vivo two or three times over a period of 2.6-6 months. The majority of neuromuscular junctions (NMJs) showed remodeling of both nerve terminals and synaptic extracellular matrix. Only 2.5% showed no changes in either synaptic element. The most commonly seen remodeling involved correlated changes in both nerve terminals and synaptic extracellular matrix. In this large group, while some junctions (20%) showed overall proportionate changes in all branches, most junctions (68%) showed disproportionate extension and/or retraction of some but not all individual branches. Another group of NMJs (9.5%) showed mismatched changes in the nerve terminal and synaptic extracellular matrix. In this group, some NMJs showed a decrease in the nerve terminal length without a corresponding reduction in synaptic extracellular matrix length. In other junctions that displayed extension of branches, the PNA-stained matrix was longer than the distal tip of the nerve terminal. Morphometric analysis indicated an average increase of 15.6% in total nerve terminal length and 13.6% in total synaptic extracellular matrix length. Although almost all NMJs displayed remodeling in at least one branch, about 50% of the 2201 individual branches examined did not show changes. The average change was 8.9% growth in the length of individual nerve terminal branches and 8.3% growth in the length of individual branches of synaptic extracellular matrix. There was no significant difference in the morphometry between the repeatedly observed junctions and the previously unobserved control junctions. Furthermore, junctions in which the synaptic extracellular matrix was longer than the nerve terminal also were seen in control as well as in experimental muscles. Cases where the nerve terminals were longer than the synaptic extracellular matrix were never observed in newly arising junctional branches. The present study has shown extensive remodeling in not only the nerve terminal but also the synaptic extracellular matrix in adult living frog NMJs. Results suggest that nerve terminals retract before the synaptic extracellular matrix. A hypothesis that extension of synaptic extracellular matrix precedes nerve terminal growth during synaptic remodeling is proposed.

Thermal response of rat fibroblasts stably transfected with the human 70-kDa heat shock protein-encoding gene

The major heat shock protein hsp70 is synthesized by cells of a wide variety of organisms in response to heat shock or other environmental stresses and is assumed to play an important role in protecting cells from thermal stress. We have tested this hypothesis directly by transfecting a constitutively expressed recombinant human hsp70-encoding gene into rat fibroblasts and examining the relationship between the levels of human hsp70 expressed and thermal resistance of the stably transfected rat cells. Successful transfection and expression of the gene for human hsp70 were characterized by RNA hybridization analysis, two-dimensional gel electrophoresis, and immunoblot analysis. When individual cloned cell lines were exposed to 45 degrees C and their thermal survivals were determined by colony-formation assay, we found that the expression of human hsp70 conferred heat resistance to the rat cells. These results reinforce the hypothesis that hsp70 has a protective function against thermal stress.