H1 histones control the epigenetic landscape by local chromatin compaction

H1 linker histones are the most abundant chromatin-binding proteins1. In vitro studies indicate that their association with chromatin determines nucleosome spacing and enables arrays of nucleosomes to fold into more compact chromatin structures. However, the in vivo roles of H1 are poorly understood2. Here we show that the local density of H1 controls the balance of repressive and active chromatin domains by promoting genomic compaction. We generated a conditional triple-H1-knockout mouse strain and depleted H1 in haematopoietic cells. H1 depletion in T cells leads to de-repression of T cell activation genes, a process that mimics normal T cell activation. Comparison of chromatin structure in normal and H1-depleted CD8+ T cells reveals that H1-mediated chromatin compaction occurs primarily in regions of the genome containing higher than average levels of H1: the chromosome conformation capture (Hi-C) B compartment and regions of the Hi-C A compartment marked by PRC2. Reduction of H1 stoichiometry leads to decreased H3K27 methylation, increased H3K36 methylation, B-to-A-compartment shifting and an increase in interaction frequency between compartments. In vitro, H1 promotes PRC2-mediated H3K27 methylation and inhibits NSD2-mediated H3K36 methylation. Mechanistically, H1 mediates these opposite effects by promoting physical compaction of the chromatin substrate. Our results establish H1 as a critical regulator of gene silencing through localized control of chromatin compaction, 3D genome organization and the epigenetic landscape.

Inpatient Neurology Consultations During the Onset of the SARS-CoV-2 New York City Pandemic: A Single Center Case Series

Objective: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) primarily causes respiratory illness. However, neurological sequelae from novel coronavirus disease 2019 (COVID-19) can occur. Patients with neurological conditions may be at higher risk of developing worsening of their underlying problem. Here we document our initial experiences as neurologic consultants at a single center quaternary hospital at the epicenter of the COVID-19 pandemic.

Methods: This was a retrospective case series of adult patients diagnosed with SARS-CoV-2 who required neurological evaluation in the form of a consultation or primary neurological care from March 13, 2020 to April 1, 2020.

Results: Thirty-three patients (ages 17–88 years) with COVID-19 infection who required neurological or admission to a primary neurology team were included in this study. The encountered neurological problems associated with SARS-CoV-2 infection were encephalopathy (12 patients, 36.4%), seizure (9 patients, 27.2%), stroke (5 patients, 15.2%), recrudescence of prior neurological disease symptoms (4 patients, 12.1%), and neuromuscular (3 patients, 9.1%). The majority of patients who required evaluation by neurology had elevated inflammatory markers. Twenty-one (63.6%) patients were discharged from the hospital and 12 (36.4%) died from COVID-19 related complications.

Conclusion: This small case series of our initial encounters with COVID-19 infection describes a range of neurological complications which are similar to presentations seen with other critical illnesses. COVID-19 infection did not change the overall management of neurological problems.

Cross-frequency coupling of alpha oscillatory power to the entrainment rhythm of a spatially attended input stream

Neural entrainment and alpha oscillatory power (8-14 Hz) are mechanisms of selective attention. The extent to which these two mechanisms interact, especially in the context of visuospatial attention, is unclear. Here, we show that spatial attention to a delta-frequency, rhythmic visual stimulus in one hemifield results in phase-amplitude coupling between the delta-phase of an entrained frontal source and alpha power generated by ipsilateral visuocortical regions. The driving of ipsilateral alpha power by frontal delta also correlates with task performance. Our analyses suggest that neural entrainment may serve a previously underappreciated role in coordinating macroscale brain networks and that inhibition of processing by alpha power can be coupled to an attended temporal structure. Finally, we note that the observed coupling bolsters one dominant hypothesis of modern cognitive neuroscience, that macroscale brain networks and distributed neural computation are coordinated by oscillatory synchrony and cross-frequency interactions.

Macronutrient composition of a morning meal and the maintenance of attention throughout the morning

BACKGROUND

At present, the impact of macronutrient composition and nutrient intake on sustained attention in adults is unclear, although some prior work suggests that nutritive interventions that engender slow, steady glucose availability support sustained attention after consumption. A separate line of evidence suggests that nutrient consumption may alter electroencephalographic markers of neurophysiological activity, including neural oscillations in the alpha-band (8-14 Hz), which are known to be richly interconnected with the allocation of attention. It is here investigated whether morning ingestion of foodstuffs with differing macronutrient compositions might differentially impact the allocation of sustained attention throughout the day as indexed by both behavior and the deployment of attention-related alpha-band activity.

METHODS

Twenty-four adult participants were recruited into a three-day study with a cross-over design that employed a previously validated sustained attention task (the Spatial CTET). On each experimental day, subjects consumed one of three breakfasts with differing carbohydrate availabilities (oatmeal, cornflakes, and water) and completed blocks of the Spatial CTET throughout the morning while behavioral performance, subjective metrics of hunger/fullness, and electroencephalographic (EEG) measurements of alpha oscillatory activity were recorded.

RESULTS

Although behavior and electrophysiological metrics changed over the course of the day, no differences in their trajectories were observed as a function of breakfast condition. However, subjective metrics of hunger/fullness revealed that caloric interventions (oatmeal and cornflakes) reduced hunger across the experimental day with respect to the non-caloric, volume-matched control (water). Yet, no differences in hunger/fullness were observed between the oatmeal and cornflakes interventions.

CONCLUSION

Observation of a relationship between macronutrient intervention and sustained attention (if one exists) will require further standardization of empirical investigations to aid in the synthesis and replicability of results. In addition, continued implementation of neurophysiological markers in this domain is encouraged, as they often produce nuanced insight into cognition even in the absence of overt behavioral changes. ClinicalTrials.gov Identifier: NCT03169283.

A single 60-min bout of peristaltic pulse external pneumatic compression transiently upregulates phosphorylated ribosomal protein s6

We investigated whether a single 60-min bout of whole leg, peristaltic pulse external pneumatic compression (EPC) altered select growth factor-related mRNAs and/or various phospho(p)-proteins related to cell growth, proliferation, inflammation and apoptosis signalling (e.g. Akt-mTOR, Jak-Stat). Ten participants (8 males, 2 females; aged 22·2 ± 0·4 years) reported to the laboratory 4 h post-prandial, and vastus lateralis muscle biopsies were obtained prior to (PRE), 1 h and 4 h post-EPC treatment. mRNA expression was analysed using real-time RT-PCR and phosphophorylated and cleaved proteins were analysed using an antibody array. No changes in selected growth factor-related mRNAs were observed following EPC. All p-proteins significantly altered by EPC decreased, except for p-rps6 (Ser235/236) which increased 31% 1 h post-EPC compared to PRE levels (P = 0·016). Notable decreases also included p-BAD (Ser112; -28%, P = 0·004) at 4 h post-EPC compared to PRE levels. In summary, an acute bout of EPC transiently upregulates p-rps6 as well as affecting other markers in the Akt-mTOR signalling cascade. Future research should characterize whether chronic EPC application promotes alterations in lower-limb musculature and/or enhances exercise-induced training adaptations.

Large-volume blood patch to multiple sites in the epidural space through a single-catheter access site for treatment of spontaneous intracranial hypotension

BACKGROUND AND PURPOSE

Spontaneous intracranial hypotension can be a therapeutic challenge to the treating physician. In this study, we present our experience with the administration of a large-volume blood patch to multiple sites in the epidural space through a single-catheter access site.

MATERIALS AND METHODS

A retrospective review was conducted of patients with spontaneous intracranial hypotension who underwent a large-volume blood patch to multiple sites in the epidural space through a single-catheter access site from 2010 to 2012. Patient demographic data, clinical charts, indications for treatment, radiographic images, procedure notes, and postprocedure hospital course were reviewed.

RESULTS

Overall, 9 patients were identified who underwent 20 blood patch procedures. Patients were selected to undergo the large-volume procedure either because they had a failed site-directed epidural blood patch or if imaging demonstrated multiple possible leak sites. There were 6 women and 3 men, with an average age of 33.5 years. The mean volume of blood injected per procedure was 54.1 mL (median=55 mL; range=38-70 mL). All patients had an orthostatic headache as one of their presenting symptoms; 22% also presented with neurocognitive decline and behavioral changes; 89% of patients had improvement or resolution of their symptoms; and 80% of patients who had a previously failed site-directed epidural blood or fibrin glue patch improved with a large volume catheter-directed blood patch.

CONCLUSIONS

Our experience supports the use of a large-volume blood patch to multiple sites in the epidural space through a single-catheter access site for the treatment of spontaneous intracranial hypotension. Additionally, our results indicate a role for this procedure in refractory cases of spontaneous intracranial hypotension.

Abstract WP75: Dual Antiplatelet Therapy in Addition to Post-Operative Heparin and Dextran Reduces Clinically Symptomatic Thromboembolic Events During Elective Aneurysm Coiling

BACKGROUND: Thromboembolism is a feared complication of coiling a cerebral aneurysm. The purpose of this study was to compare the thromboembolic events between cerebral aneurysms coiled with an anti-thromboembolic regimen versus those with no regimen.

METHODS: This retrospective cohort study included all adult patients who underwent elective coiling of an intracranial aneurysm between January 1, 2005 and February 1, 2012. All aneurysms were treated with conventional coiling. Patients were started on aspirin and clopidogrel for seven days prior to treatment with aspirin continued indefinitely and clopidogrel for 4 weeks post-coiling. During the coiling procedure patients were given heparin to maintain an activated clotting time 2.5x baseline. Additionally, dextran-40 and heparin were infused for 24 hours post coil placement. The primary endpoint was the presence of a clinically significant thromboembolic event as determine by physical exam and/or MRI diffusion weighted imaging. Each variable was analyzed for its independent association with the occurrence of an embolic event.

RESULTS: 312 aneurysms were electively treated. 261 of 312 aneurysms received our anti-thromboembolic regimen versus 51 who did not. There were a total of 6 (1.9%) embolic events. Patients who received the anti-thromboembolic regimen had 3 (1.1%) embolic events versus 3 (5.9%) in those not receiving the regimen ( p = 0.024). Patients receiving the anti-thromboembolic regimen had significantly more active tobacco use but the two groups did not differ in age, sex, or the presence of obesity, diabetes, or hypercoagulable state. There was no difference in the occurrence of central nervous system or systemic hemorrhages between the two groups. In univariate analysis, the presence of a hypercoagulable state ( p = 0.014) and the lack of anti-embolic regimen ( p = 0.043) were associated with the occurrence of an embolic event. Both remained significant in multivariate analysis ( p = 0.016 and p = 0.048, respectively).

CONCLUSION: An anti-thromboembolic regimen consisting of dual antiplatelet therapy plus post-operative heparin and dextran reduced the risk of embolic events during elective aneurysm coiling. This regimen was safe, with no observed increase in hemorrhagic complications.

A study of the killer cell immunoglobulin-like receptor gene KIR2DS1 in a Caucasoid Brazilian population with psoriasis vulgaris

Psoriasis is a chronic inflammatory skin disease whose pathogenesis and genetic background remain unclear. Considering that previous studies have suggested an association of psoriasis vulgaris (PV) and killer cell immunoglobulin-like receptors (KIRs), we typed 15 KIR genes and human leukocyte antigen (HLA)-Cw in 79 Brazilian Caucasoid patients with PV and 110 healthy controls by polymerase chain reaction (PCR) using sequence-specific oligonucleotides and sequence-specific primers. We did not observe a relevant increase in the frequency of the activating KIR2DS1 gene in the PV group [KIR2DS1, 46 of 79 cases (58.2%) vs 40 of 110 controls (36.4%)]. However, an association of KIR2DS1 with Cw*0602+ in 26.5% of PV patients was observed, while it was present in only 5.4% of controls. These results suggest that activating KIR2DS1 gene may not confer susceptibility to PV, and an association of KIR2DS1 gene with the HLA-Cw*0602+ was observed in these patients.

Folding and catalysis of the hairpin ribozyme

The active form of the hairpin ribozyme is brought about by the interaction of two formally unpaired loops. In a natural molecule, these are present on two adjacent arms of a four-way junction. Although activity can be obtained in molecules lacking this junction, the junction is important in the promotion of the folded state of the ribozyme under physiological conditions, at a rate that is faster than the chemical reaction. Single-molecule fluorescence resonance energy transfer studies show that the junction introduces a discrete intermediate into the folding process, which repeatedly juxtaposes the two loops and thus promotes their docking. Using single-molecule enzymology, the cleavage and ligation rates have been measured directly. The pH dependence of the rates is consistent with a role for nucleobases acting in general acid-base catalysis.

A new Fc receptor homolog, FREB2, found in germinal center B cells

Fc receptor homologs are a recently identified family of proteins homologous to FcgammaRI, found on human and mouse B cells. One of these, FREB/FcRX/FCRL, was found to be unique since it lacks a transmembrane domain and is expressed intracellularly within germinal center B cells. We have identified in humans and mice a new Fc receptor homolog, FREB2, that blends conserved elements of the classical Fc gamma receptors with structural motifs previously thought to be unique to FREB1. This protein is comprised of three immunoglobulin-like domains with high homology to those in FcgammaRI, and a C-terminus containing a proline-rich stalk region followed by a leucine-rich amphipathic alpha helix. Like FREB1, FREB2 is expressed as an intracellular protein. In murine splenocytes, RNA transcripts for each of the two proteins can be amplified from germinal center B cells. However, immunohistochemical analysis of human tonsils indicates that expression of FREB1 and FREB2 is mutually exclusive in non-neoplastic cells. Importantly, FREB2 expression within human tonsils appears to be limited to a small subset of nonproliferating germinal center B cells, suggesting that it may play a role in regulating clonal expansion or differentiation of B cells during the germinal center reaction.

Single-molecule studies of DNA and RNA four-way junctions

Branched helical junctions are common in nucleic acids. In DNA, the four-way junction (Holliday junction) is an essential intermediate in homologous recombination and is a highly dynamic structure, capable of stacking conformer transitions and branch migration. Our single-molecule fluorescence studies provide unique insight into the energy landscape of Holliday junctions by visualizing these processes directly. In the hairpin ribozyme, an RNA four-way junction is an important structural element that enhances active-site formation by several orders of magnitude. Our single-molecule studies suggest a plausible mechanism for how the junction achieves this remarkable feat; the structural dynamics of the four-way junction bring about frequent contacts between the loops that are needed to form the active site. The most definitive evidence for this is the observation of three-state folding in single-hairpin ribozymes, the intermediate state of which is populated due to the intrinsic properties of the junction.

ETS2 overexpression in transgenic models and in Down syndrome predisposes to apoptosis via the p53 pathway

ETS2 is a transcription factor encoded by a gene on human chromosome 21 and alterations in its expression have been implicated in the pathophysiological features of Down syndrome (DS). This study demonstrates that overexpression of ETS2 results in apoptosis. This is shown in a number of circumstances, including ETS2-overexpressing transgenic mice and cell lines and in cells from subjects with DS. Indeed we report for the first time that the ETS2 overexpression transgenic mouse develops a smaller thymus and lymphocyte abnormalities similar to that observed in DS. In all circumstances of ETS2 overexpression, the increased apoptosis correlated with increased p53 and alterations in downstream factors in the p53 pathway. In the human HeLa cancer cell line, transfection with functional p53 enables ETS2 overexpression to induce apoptosis. Furthermore, crossing the ETS2 transgenic mice with p53(-/-) mice genetically rescued the thymic apoptosis phenotype. Therefore, we conclude that overexpression of human chromosome 21-encoded ETS2 induces apoptosis that is dependent on p53. These results have important consequences for understanding DS and oncogenesis and may provide new insights into therapeutic interventions.

Transformation induced by Ewing's sarcoma associated EWS/FLI-1 is suppressed by KRAB/FLI-1

Ewing's sarcoma is a childhood bone tumour with poor prognosis, most commonly associated with a t(11;22)(q24;q12) reciprocal translocation that fuses the EWS and FLI-1 genes, resulting in the production of an aberrant chimeric transcription factor EWS/FLI-1. To elucidate the mechanisms by which EWS/FLI-1 mediates transformation in mouse models, we have generated a murine Ews/Fli-1 fusion protein. We demonstrate that this protein transforms fibroblast cells in vitro similar to human EWS/FLI-1 as demonstrated by serum and anchorage-independent growth, the formation of tumours in nude mice and elevation of the oncogenic marker c-myc. Furthermore, transformation of these cells was inhibited by a specific repressor, KRAB/FLI-1. The KRAB/FLI-1 repressor also suppressed the tumorigenic phenotype of a human Ewing's sarcoma cell line. These findings suggest that the transformed phenotype of Ewing's sarcoma cells can be reversed by using the sequence-specific FLI-1-DNA-binding domain to target a gene repressor domain. The inhibition of EWS/FLI-1 is the first demonstration of the KRAB domain suppressing the action of an ETS factor. This approach provides potential avenues for the elucidation of the biological mechanisms of EWS/FLI-1 oncogenesis and the development of novel therapeutic strategies.

The A730 loop is an important component of the active site of the VS ribozyme

The core of the VS ribozyme comprises five helices, that act either in cis or in trans on a stem-loop substrate to catalyse site-specific cleavage. The structure of the 2-3-6 helical junction indicates that a cleft is formed between helices II and VI that is likely to serve as a receptor for the substrate. Detailed analysis of sequence variants suggests that the base bulges of helices II and VI play an architectural role. By contrast, the identity of the nucleotides in the A730 loop is very important for ribozyme activity. The base of A756 is particularly vital, and substitution by any other nucleotide or ablation of the base leads to a major reduction in cleavage rate. However, variants of A756 bind substrate efficiently, and are not defective in global folding. These results suggest that the A730 loop is an important component of the active site of the ribozyme, and that A756 could play a key role in catalysis.

Lewis antigen expression by Helicobacter pylori

Although Helicobacter pylori express Lewis antigens as a component in the lipopolysaccharide, their role in the infectious process is not well understood. Lewis antigen expression with growth phase was investigated, as well as the distribution of Lewis antigens among isolates from asymptomatic and symptomatic individuals. Lewis antigens are expressed by H. pylori in a growth phase-dependent manner, with the greatest expression occurring in the logarithmic phase of growth. As growth proceeds, an increasing amount of Lewis antigens are shed into the culture supernatant. Lewis antigen expression among H. pylori isolates from asymptomatic individuals is characterized by an absence of type I Lewis antigens, a decrease in Le(x) expression, and an increase in nontypeable H. pylori, as compared with that among H. pylori isolates from symptomatic patients. The data support a role for Lewis antigens in the pathogenesis associated with symptomatic H. pylori infection in colonized individuals.

Spontaneous mutations that confer antibiotic resistance in Helicobacter pylori

In this study, we systematically examined in vitro frequencies and spectra of the spontaneous mutations in Helicobacter pylori that confer resistance to clarithromycin (Cla(r)), metronidazole (Mtz(r)), amoxicillin (Amx(r)), ciprofloxacin (Cip(r)), and rifampin (Rif(r)). The mutation rate of Rif(r) or Cip(r) determined in a fluctuation assay is 1 x 10(-8) to 2 x 10(-8) per cell per division. In contrast, the mutation rates of Cla(r), Mtz(r), and Amx(r) are much lower (<10(-9)). However, Mtz(r) mutants could be readily selected in vitro by using the serial passage method, suggesting that the mutagenic effect and selective effect of a sublethal dose of metronidazole contribute to the rapid development of Mtz(r). Analysis of spontaneous Rif(r), Cla(r), and Cip(r) mutants confirmed previous results indicating that mutations within the rpoB gene, the 23S rRNA gene, and the gyrA gene, respectively, are responsible; also, several new mutant alleles were identified. Mtz(r) mutants resulted most frequently, but not always, from mutations in the rdxA gene. DNA fragments containing each mutant allele could readily transform susceptible H. pylori strains to resistance, confirming that each mutant allele is responsible for the resistance phenotype.

Importance of specific nucleotides in the folding of the natural form of the hairpin ribozyme

The hairpin ribozyme in its natural context consists of two loops in RNA duplexes that are connected as arms of a four-way helical junction. Magnesium ions induce folding into the active conformation in which the two loops are in proximity. In this study, we have investigated nucleotides that are important to this folding process. We have analyzed the folding in terms of the cooperativity and apparent affinity for magnesium ions as a function of changes in base sequence and functional groups, using fluorescence resonance energy transfer. Our results suggest that the interaction between the loops is the sum of a number of component interactions. Some sequence variants such as A10U, G+1A, and C25U exhibit loss of cooperativity and reduced affinity of apparent magnesium ion binding. These variants are also very impaired in ribozyme cleavage activity. Nucleotides A10, G+1, and C25 thus appear to be essential in creating the conformational environment necessary for ion binding. The double variant G+1A/C25U exhibits a marked recovery of both folding and catalytic activity compared to either individual variant, consistent with the proposal of a triple-base interaction among A9, G+1, and C25 [Pinard, R., Lambert, D., Walter, N. G., Heckman, J. E., Major, F., and Burke, J. M. (1999) Biochemistry 38, 16035-16039]. However, substitution of A9 leads to relatively small changes in folding properties and cleavage activity, and the double variant G+1DAP/C25U (DAP is 2,6-diaminopurine), which could form an isosteric triple-base interaction, exhibits folding and cleavage activities that are both very impaired compared to those of the natural sequence. Our results indicate an important role for a Watson--Crick base pair between G+1 and C25; this may be buttressed by an interaction with A9, but the loss of this has less significant consequences for folding. 2'-Deoxyribose substitution leads to folding with reduced magnesium ion affinity in the following order: unmodified RNA > dA9 > dA10 > dC25 approximately dA10 plus dC25. The results are interpreted in terms of an interaction between the ribose ring of C25 and the ribose and base of A10, in agreement with the proposal of Ryder and Strobel [Ryder, S. P., and Strobel, S. A. (1999) J. Mol. Biol. 291, 295-311]. In general, there is a correlation between the ability to undergo ion-induced folding and the rate of ribozyme cleavage. An exception to this is provided by G8, for which substitution with uridine leads to severe impairment of cleavage but folding characteristics that are virtually unaltered from those of the natural species. This is consistent with a direct role for the nucleobase of G8 in the chemistry of cleavage.

The folding of the hairpin ribozyme: dependence on the loops and the junction

In its natural context, the hairpin ribozyme is constructed around a four-way helical junction. This presents the two loops that interact to form the active site on adjacent arms, requiring rotation into an antiparallel structure to bring them into proximity. In the present study we have compared the folding of this form of the ribozyme and subspecies lacking either the loops or the helical junction using fluorescence resonance energy transfer. The complete ribozyme as a four-way junction folds into an antiparallel structure by the cooperative binding of magnesium ions, requiring 20-40 microM for half-maximal extent of folding ([Mg2+]1/2) and a Hill coefficient n = 2. The isolated junction (lacking the loops) also folds into a corresponding antiparallel structure, but does so noncooperatively (n = 1) at a higher magnesium ion concentration ([Mg2+]1/2 = 3 mM). Introduction of a G + 1A mutation into loop A of the ribozyme results in a species with very similar folding to the simple junction, and complete loss of ribozyme activity. Removal of the junction from the ribozyme, replacing it either with a strand break (serving as a hinge) or a GC5 bulge, results in greatly impaired folding, with [Mg2+]1/2 > 20 mM. The results indicate that the natural form of the ribozyme undergoes ion-induced folding by the cooperative formation of an antiparallel junction and loop-loop interaction to generate the active form of the ribozyme. The four-way junction thus provides a scaffold in the natural RNA that facilitates the folding of the ribozyme into the active form.

Fluorescence resonance energy transfer as a structural tool for nucleic acids

Fluorescence resonance energy transfer is a spectroscopic method that provides distance information on macromolecules in solution in the range 20-80 A. It is particularly suited to the analysis of the global structure of nucleic acids because the long-range distance information provides constraints when modelling these important structures. The application of fluorescence resonance energy transfer to nucleic acid structure has seen a resurgence of interest in the past decade, which continues to increase. An especially exciting development is the recent extension to single-molecule studies.

Early growth response (Egr)-1 gene induction in the thymus in response to TCR ligation during early steps in positive selection is not required for CD8 lineage commitment

The early growth response gene 1 (Egr-1) is induced during positive selection in the thymus and has been implicated in the differentiation of CD4+ thymocytes. Here, we show that signals that specifically direct CD8 lineage commitment also induce Egr-1 DNA-binding activity in the nucleus. However, we find that pharmacological inhibition of mitogen-activated protein kinase/extracellular signal-related kinase kinase activity potently inhibits Egr-1 DNA-binding function at concentrations that promote differentiation of CD8+ thymocytes, suggesting Egr-1 activity is not essential for CD8 commitment. To further determine the role of Egr-1 in thymocyte development, we compare steady-state Egr-1 DNA-binding activity in thymocytes from mice with defined defects in positive selection. The data indicate that the appearance of functional Egr-1 is downstream of signals induced by TCR/MHC engagement, whereas it is less sensitive to alterations in Lck-mediated signals, and does not correlate directly with proficient positive selection. Egr-1 is one of the earliest transcription factors induced upon TCR ligation on immature thymocytes, and plays a potential role in the transcription of genes involved in thymocyte selection.

Lewis antigen expression and stability in Helicobacter pylori isolated from serial gastric biopsies

The expression of Lewis antigens by the gastric pathogen Helicobacter pylori in serial biopsy isolates was investigated to assess antigen distribution and stability. A total of 26 asymptomatic subjects were given various doses of 3' sialyllactose for up to 56 days. Gastric biopsies were performed during the dosing period, as well as 30 days after dosing, which provided 127 H. pylori isolates that were examined by use of ELISA and immunoblot. A large proportion of subjects (14/26) yielded sequential H. pylori isolates, which appeared genetically identical but had variable Lewis antigen expression. The proportion of subjects with H. pylori isolates not expressing any Lewis antigens was greater than that previously reported (10/26). Thus, the expression of the Lewis antigens by H. pylori does not appear to be a requirement for colonization, whereas the antigen expression after human infection is more variable than the previously reported rate observed with in vitro cultures.

Analysis of a ptsH homologue from Streptomyces coelicolor A3(2)

A ptsH homologue of Streptomyces coelicolor A3(2) was identified in the emerging genome sequence, cloned in Escherichia coli and the S. coelicolor HPr over-produced and purified. The protein was phosphorylated in vitro in a phosphoenolpyruvate (PEP)-dependent manner by purified enzyme I (EI) from Bacillus subtilis, and much less efficiently in an ATP-dependent manner by purified HPr kinase, also from B. subtilis. There was no indication of ATP-dependent phosphorylation of the purified protein by cell extracts of either S. coelicolor or Streptomyces lividans. Deletion of the ptsH homologue from the S. coelicolor and S. lividans chromosomes had no effect on growth when fructose was supplied as sole carbon source, and in S. coelicolor it had no effect on glucose repression of agarase and galactokinase synthesis, suggesting that the HPr encoded by this gene does not play an essential role in fructose transport nor a general role in carbon catabolite repression.

Elevated immunoglobulin E (IgE) levels in children with exposure to environmental lead

Lead has been reported to be an immunosuppressive agent in animal systems at levels far below those recognized as overtly toxic. Little data exist on lead's effects on the human immune system, especially in young children who are at greatest risk for exposure to this environmental hazard. The effects of environmental lead exposure on the human immune system were examined in a population of young children, age 9 months-6 years, from the urban population of Springfield-Greene County, Missouri. Reported here are data from 279 children with blood lead levels ranging from 1 to 45 microg/dl. White blood cell populations have been enumerated and examined for cell surface expression of activation markers. Serum has been analyzed for IgE, specific titers to Rubella vaccine, sCD25 (the soluble form of the IL2 receptor), sCD27 (the soluble form of the lymphocyte specific member of the tumor necrosis factor receptor family), and IL4 (the cytokine interleukin 4). Variation of these assays with age of the child was considered in statistical analysis of data. A statistically significant relationship of IgE and blood lead level was found in this population; as blood lead (PbB) level increases, IgE level increases. No other statistically significant differences between risk categories or other associations with blood lead level were found. The exact mechanism for this apparent stimulus of IgE-producing B cells remains to be elucidated. The development of allergic symptoms is often preceded by an increase in IgE. These data indicate that ingested lead could play a role in this process by stimulating IgE production.

Visualizing ion relaxation in the transport of short DNA fragments

Ion relaxation plays an important role in a wide range of phenomena involving the transport of charged biomolecules. Ion relaxation is responsible for reducing sedimentation and diffusion constants, reducing electrophoretic mobilities, increasing intrinsic viscosities, and, for biomolecules that lack a permanent electric dipole moment, provides a mechanism for orienting them in an external electric field. Recently, a numerical boundary element method was developed to solve the coupled Navier-Stokes, Poisson, and ion transport equations for a polyion modeled as a rigid body of arbitrary size, shape, and charge distribution. This method has subsequently been used to compute the electrophoretic mobilities and intrinsic viscosities of a number of model proteins and DNA fragments. The primary purpose of the present work is to examine the effect of ion relaxation on the ion density and fluid velocity fields around short DNA fragments (20 and 40 bp). Contour density as well as vector field diagrams of the various scalar and vector fields are presented and discussed at monovalent salt concentrations of 0.03 and 0.11 M. In addition, the net charge current fluxes in the vicinity of the DNA fragments at low and high salt concentrations are briefly examined and discussed.

Two beta-tubulin genes, TUB1 and TUB8, of Arabidopsis exhibit largely nonoverlapping patterns of expression

Chimeric reporter genes were used to investigate the patterns of expression of two beta-tubulin genes, TUB1 and TUB8, in Arabidopsis thaliana. The TUB1 chimeric gene was preferentially expressed in epidermal and cortical cells of primary roots, whereas the TUB8 chimeric gene was preferentially expressed in the endodermal and phloem cells of primary roots and in the vascular tissues of leaves, stems, and flowers of transgenic plants.

An apparatus for membrane-confined analytical electrophoresis

A membrane-confined analytical electrophoresis apparatus for measuring the solution charge of macromolecules has been described previously (T. M. Laue et al., Anal. Biochem. 1989, 182, 377-382). Presented here is a design for this apparatus, which permits the on-line acquisition and display of absorbance data from up to 512 positions along an analysis chamber. Concentration distributions of macromolecules in solution can be monitored in the chamber to provide steady-state electrophoresis, electrophoretic mobility and diffusion measurements. Buffer chambers press semipermeable membranes against the open ends of a fused-silica cuvette to form the analysis chamber. This configuration permits both the flow of buffer and the establishment of an electric field across the cuvette, while retaining macromolecules in the field of view. Though a gel may be included in the analysis chamber, none is required for gradient stabilization. The volume of sample required for analysis is 8 microL, most of which is recoverable. Experimental conditions can be varied during study by simply changing the circulating buffer and/or the electric field. The analysis and buffer chambers are held in an aluminum housing that sits in an aluminum water jacket. The water jacket provides temperature control, shielding from external electrical noise and also serves as an optical mask. Plans for the cell assembly, optical system and the computer interface for data acquisition are provided. The assembly and operation of the apparatus and the analysis of data are described.

The rpfA gene of Xanthomonas campestris pathovar campestris, which is involved in the regulation of pathogenicity factor production, encodes an aconitase

Xanthomonas campestris pv campestris (Xcc) is a plant pathogenic bacterium that controls the production of pathogenicity factors in part by a cluster of genes designated rpf (regulation of pathogenicity factors). Sequence analysis of one of these genes (rpfA) revealed an open reading frame with amino acid sequence similarity to aconitases from other bacteria. Aconitase activity was lower in cellular extracts of an rpfA::Tn5 mutant than in those from the wild type. A zymogram of aconitase activity after native gel electrophoresis showed the presence of two distinct aconitases in Xcc; the major aconitase was absent in the rpfA::Tn5 mutant. This mutant also had reduced levels of extracellular enzymes and extracellular polysaccharide (EPS). Supplying rpfA in trans to the rpfA::Tn5 mutant restored both the major aconitase activity and the synthesis of these pathogenicity factors. The transcription of the genes for two extracellular enzymes (prtA, encoding a serine protease, and engXCA, encoding endoglucanase) was reduced in the rpfA mutant background. Because some eukaryotic aconitases are also involved in iron regulation, we explored a possible connection between rpfA and iron metabolism. Intracellular iron levels in the mutants were lower than in the wild type as assessed by sensitivity to the iron-activated antibiotic, streptonigrin. Wild-type bacteria grown in iron-deficient conditions had a similar sensitivity to streptonigrin as the aconitase mutant. Overall, these results suggest that a prokaryotic aconitase can also act as a regulator of gene expression and that the regulation is possibly related to changes in intracellular iron levels.

A novel regulatory system required for pathogenicity of Xanthomonas campestris is mediated by a small diffusible signal molecule

Mutations in the seven clustered rpf genes cause downregulated synthesis of extracellular enzymes and reduced virulence of Xanthomonas campestris pathovar campestris (Xcc). The phenotype of mutants in one of the genes, rpfF, can be restored by a diffusible extracellular factor (DSF) produced by all Xcc strains tested, apart from rpfF and rpfB mutants. DSF accumulates in early stationary phase (when synthesis of enzymes is maximal), but levels decline subsequently. Addition of DSF to exponentially-growing wild-type bacteria does not cause precocious enzyme synthesis. rpfB and rpfF are expressed throughout growth, but the rate increases in early stationary phase. RpfB is predicted to be a long-chain fatty acyl CoA ligase, and RpfF shows some relatedness to enoyl CoA hydratases. The properties of DSF suggest that it may be a fatty-acid derivative, and certain lipid preparations possess DSF activity at higher concentrations. These include lipid extracts and acid-hydrolysed lipoplysaccharide and lipid A from Xcc, and purified dodecanoic and hydroxydodecanoic acid. DSF production is confined to certain xanthomonads. We propose a model for the DSF system, which represents a novel mechanism for regulating virulence factor synthesis in response to physiological or environmental changes.

Effector-induced self-association and conformational changes in the enhancer-binding protein NTRC

The Klebsiella pneumoniae nitrogen regulatory protein NTRC is a response regulator which activates transcription in response to nitrogen limitation, and is a member of the family of sigma N-dependent enhancer-binding proteins. Using limited trypsin digestion, two domains of NTRC were detected and conformational changes within the protein in response to the binding of ligands were also observed. In the absence of ligands, the major digestion products were 42, 36 and 12.5 kDa bands corresponding to the central plus C-terminal domain, the central domain, and the N-terminal domains, respectively. Upon binding of purine but not pyrimidine nucleotides, the 36 kDa band was insensitive to further proteolysis, indicative of a conformational change in the central domain. Analysis of the dependence of this insensitivity on ATP gamma S concentration suggested an apparent dissociation constant (Kd) for ATP gamma S of 150 microM. In the presence of DNA, both the central and C-terminal domains of NTRC were insensitive to proteolytic cleavage, indicative of a further conformational change. NTRC S160F, a mutant form of NTRC that is active in the absence of phosphorylation, was more stable to proteolysis than the wild-type protein. This mutant protein is apparently locked in a conformation resembling the DNA-bound form of wild-type NTRC. The involvement of ligands in self-association was studied using sedimentation equilibrium analysis. In the absence of ligand, wild-type NTRC displayed a monomer-dimer equilibrium with a Kd of 6 microM. In the presence of ATP gamma S the equilibrium was shifted towards the dimer form (Kd = 0.8 microM). A similar dissociation constant for the monomer-dimer interaction was observed with NTRC S160F in the absence of ATP gamma S (Kd = 0.5 microM). The addition of ATP gamma S induced a significant association of NTRC S160F to higher-order states with a dimer-octamer model producing a slightly, but not significantly better fit to the data than a dimer-hexamer model. We propose that ligand-mediated self-association provides a common mechanism for activation of this class of transcriptional regulatory proteins.

Insights from a new analytical electrophoresis apparatus

Charge is a fundamental property of macromolecules that is inextricably linked to their structure, solubility, stability, and interactions. Progress has been made on the theoretical and structural aspects of these relationships. However, for several reasons, charge is difficult to measure in solution. Consequently, there is a lack of experimental data that, independent of other macro-ion properties, determines the effective charge. To overcome this problem, novel instrumentation and methods are being developed in our laboratory. Described here is an analytical electrophoresis apparatus that permits both the measurement of electrophoretic mobilities and the determination of steady-state electrophoresis concentration distributions. The latter provides a different-perspective on the processes that influence macro-ion behavior in an electric field. In addition, the apparatus permits the determination of diffusion coefficients either from boundary spreading during transport or from the decay of a concentration gradient. All of these determinations can be made with a single, 8-microL sample in a variety of solvents, thus providing unique insights into the charge properties of a macro-ion. Presented here is a progress report about this emerging technology, including the description of a prototype apparatus and examples of its use with a DNA oligonucleotide.

Cloning and characterization of the rpfC gene of Xanthomonas oryzae pv. oryzae: involvement in exopolysaccharide production and virulence to rice

rpfC is one of a cluster of genes which coordinately regulate the synthesis of extracellular enzymes and exopolysaccharide and pathogenicity in Xanthomonas campestris pv. campestris, the black rot pathogen of brassicas. An rpfC homolog which could functionally complement an rpfC mutant of X. campestris pv. campestris was identified in Xanthomonas oryzae pv. oryzae and the gene was characterized. Mutation of this gene in X. oryzae pv. oryzae had no effect on extracellular enzymes, but exopolysaccharide synthesis and virulence to rice were substantially reduced.

A gene for superoxide dismutase from Xanthomonas campestris pv. campestris and its expression during bacterial-plant interactions

A recombinant plasmid selected from a library of Xanthomonas campestris pv. campestris genomic DNA by functional complementation of a superoxide dismutase (SOD)-deficient strain of Escherichia coli contained a gene encoding the major SOD activity of X. campestris pv. campestris. Inhibition and renaturation studies suggested that manganese was the metal cofactor for this SOD. Examination of the nucleotide sequence of an active subclone revealed a 612-bp open reading frame that encodes a protein with high amino acid sequence homology to a range of SOD enzymes. The sod gene was mutagenized with Tn5-lacZ. None of the insertions that abolished SOD-conferring activity were in the correct orientation for lacZ expression. Repeated attempts to introduce these insertions into the chromosome of X. campestris pv. campestris were unsuccessful and it was concluded that the sod gene may be essential for viability. In order to monitor the expression of the sod gene, a sod-gus transcriptional fusion was constructed. Expression of the sod gene varied according to the growth stage of the organism in culture. In planta, the sod gene was induced within 3 to 4 h of inoculation, with similar kinetics during compatible and incompatible interactions with turnip and pepper, respectively.

Down's syndrome-like skeletal abnormalities in Ets2 transgenic mice

Expression of Ets2, a proto-oncogene and transcription factor, occurs in a variety of cell types. During murine development it is highly expressed in newly forming cartilage, including in the skull precursor cells and vertebral primordia. Ets2 is located on human chromosome 21 (ref. 8) and is overexpressed in Down's syndrome (trisomy 21). Here we generate transgenic mice to investigate the consequences of overexpression of Ets2. We find that mice with less than 2-fold Ets2 overexpression in particular organs develop neurocranial, viscerocranial and cervical skeletal abnormalities. These abnormalities have similarities with the skeletal anomalies found in trisomy-16 mice and humans with Down's syndrome, in which the gene dosage of Ets2 is increased. Our results indicate that Ets2 has a role in skeletal development and implicate the overexpression of Ets2 in the genesis of some skeletal abnormalities that occur in Down's syndrome.

Phytochrome A and phytochrome B mediate the hypocotyl-specific downregulation of TUB1 by light in arabidopsis

Arabidopsis contains six alpha-tubulin and nine beta-tubulin genes that are expressed in a tissue-specific and developmentally regulated manner. We analyzed the effects of light on tubulin mRNA abundance in Arabidopsis seedlings using RNA gel blot hybridizations and gene-specific probes. Transcript levels of all 15 tubulin genes were decreased by continuous white light, although to different degrees. Detailed analysis was performed with the beta-tubulin TUB1 gene. The transcript level of TUB1 was high in etiolated seedlings and decreased to approximately 20% of the dark mRNA level after 2 to 6 hr of white light treatment. We showed that this downregulation requires high-irradiance light treatment and that multiple photoreceptors are involved. In particular, using phytochrome mutants and narrow wave band light, we demonstrated that both the phytochrome A (phyA)-mediated far-red light high-irradiance response and the phytochrome B (phyB)-mediated red light high-irradiance response are involved in the downregulation of TUB1 expression by white light. Histochemical analysis of transgenic plants expressing a TUB1-beta-glucuronidase chimeric transgene indicated that the downregulation observed only in hypocotyls and not in roots is controlled transcriptionally.

A locus determining pathogenicity of Xanthomonas campestris is involved in lipopolysaccharide biosynthesis

A pathogenicity locus in Xanthomonas campestris pv. campestris has been shown to comprise two genes which mediate biosynthesis of the bacterial lipopolysaccharide (LPS) but not extracellular polysaccharide. Mutants with Tn5 insertions in either gene showed alterations in the electrophoretic patterns of both water-soluble and phenol-soluble LPS forms, which suggested defects in the biosynthesis of the core oligosaccharide component. On gel chromatography, core oligosaccharides of the mutants were of apparently lower molecular weight than those from the wild type. Furthermore, the content of mannose and glucose, sugars characteristic of the core oligosaccharide, were significantly lower in the water-soluble LPS of the mutants. Because of their role in LPS core biosynthesis, the two genes were called rfaX and rfaY. rfaX mutants show altered behavior in a range of host and non-host plants such that the number of recoverable bacteria drop within the first 24 h after inoculation. In contrast, the behavior of rfaY mutants only differed from the wild type in Datura, a non-host plant in which the growth of the wild type is severely attenuated. The predicted protein RfaY showed significant sequence homology to a sub-family of RNA polymerase sigma factors which are involved in extracytoplasmic functions.

Evidence for two aromatic amino acid-binding sites, one ATP-dependent and the other ATP-independent, in the Escherichia coli regulatory protein TyrR

In Escherichia coli, genetic regulation of aromatic amino acid biosynthesis and uptake is effected by the protein TyrR, which acts via ligand-mediated repression and activation. Characterization of the interactions of tyrosine, phenylalanine and tryptophan with TyrR revealed the presence of two separate aromatic amino acid-binding sites, one ATP-dependent, the other ATP-independent. Binding to the ATP-dependent site induces the self-association of TyrR. Using sedimentation equilibrium analyses, dissociation constants for this site in the dimeric and hexameric forms of TyrR were determined to be 330 microM and 24 microM, respectively, for tyrosine, and 55 mM and 3.7 mM, respectively, for phenylalanine. Tryptophan bound with a strength similar to that of phenylalanine, and both phenylalanine and tryptophan competed with the binding of tyrosine. The ATP-independent site, which has not been observed previously, was characterized by ultraviolet (u.v.) difference spectroscopy and a sedimentation-velocity meniscus-depletion method. Phenylalanine bound co-operatively to this site, exhibiting half-saturation at 260 microM. Tryptophan competed weakly with phenylalanine, half-saturation occurring at 1.2 mM. No binding of tyrosine to this site could be detected. We propose that the binding of phenylalanine or tryptophan to this ATP-independent site is responsible for phenylalanine- and tryptophan-mediated regulation by TyrR.

Analysis of an Escherichia coli mutant TyrR protein with impaired capacity for tyrosine-mediated repression, but still able to activate at sigma 70 promoters

In Escherichia coli, TyrR represses and activates transcription of operons required for tyrosine, phenylalanine and tryptophan biosynthesis and uptake. The TyrR central domain is homologous with NtrC and some other bacterial regulatory proteins, although TyrR regulates sigma 70, not sigma 54, promoters. We isolated a central domain TyrR mutant (TyrR E274Q) by substitution of a normally conserved amino acid. The mutant was unable to bring about tyrosine-mediated repression of aroF, aroL, tyrB, and tyrP and had diminished capability for tyrosine- and phenylalanine-mediated repression of aroP. In contrast, it was able to effect wild-type levels of phenylalanine-mediated repression of aroG, tryptophan-mediated repression of aroP and transcriptional activation of mtr and tyrP. The binding of purified TyrR E274Q to ATP (a requirement for tyrosine binding) and to the strong TyrR box of tyrP operator DNA were normal, but tyrosine binding and tyrosine-dependent hexamerization were significantly impaired. These properties are consistent with the proposal that self association is essential for tyrosine-mediated repression by TyrR but not for tyrosine- or phenylalanine-mediated activation. E274 of TyrR must participate in either the binding of tyrosine, or the coupling of ATP binding with a conformational change that alters the affinity of the ATP-dependent aromatic amino acid-binding site.

Decreased natural killer cell activity in endometriosis patients: relationship to disease pathogenesis

A number of reports have measured NK cell activity in patients with endometriosis with varied results. Therefore we have examined the NK activity of PBL from 44 gynecological patients undergoing laparoscopy. This analysis has demonstrated a significant reduction in NK activity only in more severe stages of endometriosis (stages III and IV) relative to patients with milder disease and controls. These data indicate that decreased NK activity is unlikely to be a primary etiological factor in the development of endometriosis but may indicate that decreased NK activity is related to the development of the more frequent and/or larger lesions characteristic of severe endometriosis. These data could indicate potential for immunotherapy of patients with advanced endometriosis by the upregulation of NK activity in vivo.

Ligand-induced self-association of the Escherichia coli regulatory protein TyrR

Analyses of the sedimentation properties of the Escherichia coli regulatory protein TyrR indicated that it undergoes a ligand-induced hexamerization. This phenomenon was observed at protein concentrations approximating to those found in vivo. In the absence of added ligands, TyrR sedimented as a single molecular species with a sedimentation coefficient of 5.3 S and a relative molecular mass of 113,000. Given a subunit relative molecular mass of 57,640 for TyrR, it was concluded that this species is a dimer. Similar sedimentation properties were observed when TyrR was sedimented in the presence of either tyrosine, phenylalanine, ATP or ATP gamma S, a non-hydrolysable analogue of ATP. However, in the presence of saturating ATP gamma S and 500 microM tyrosine or 25 mM phenylalanine the sedimentation behaviour of TyrR yielded relative molecular masses of 340,000 and 310,000, respectively, indicative of hexamer formation. The sedimentation data obtained across a range of TyrR concentrations fitted equally well to dimer-hexamer and dimer-tetramer-hexamer models. For the latter model, the predicted overall association constant was 3.2 x 10(13) M-2 at saturating tyrosine, while the relative values of the association constants for the two individual steps indicated a concerted mechanism with the tetramer a minor component. There was no indication of dimer dissociation when dilute TyrR solutions (100 nM) were sedimented. A model to explain the role of hexamerization in tyrosine-mediated repression of transcription by TyrR is proposed. It is suggested that the hexameric form of TyrR is the active repressing species, interacting with two or three specific sequences (TyrR boxes) in the targeted regulatory DNA. The hexamerization reaction that takes place when the tyrosine concentration rises is envisaged as occurring in situ on the DNA, with a TyrR dimer that permanently occupies one of the TyrR boxes acting as a nucleation site for the development of the hexamer-DNA complex.

Purification of the Escherichia coli regulatory protein TyrR and analysis of its interactions with ATP, tyrosine, phenylalanine, and tryptophan

A plasmid that directs the overexpression of the Escherichia coli regulatory protein TyrR was constructed. Cell extracts of an E. coli strain harboring the plasmid were used to develop a two-step procedure for purifying homogeneous TyrR. The weight-average molecular weight of the pure protein was determined by sedimentation equilibrium analyses to be 110,000 +/- 5,000, indicating that native TyrR is a homodimer. The binding of ligands to TyrR was investigated by the techniques of sedimentation velocity meniscus depletion and steady state dialysis. One mol of ATP bound per mol of TyrR subunit with half-maximal saturation at 5-7 microM ATP. ATP binding curves exhibited positive cooperativity, with a value of 1.3 for the Hill constant, nH. The binding was not significantly affected by the presence of either 500 microM tyrosine or 2 mM phenylalanine. Binding of tyrosine to TyrR (40 microM subunit) could not be detected in the absence of ATP, indicating that the TyrR-tyrosine complex has a dissociation constant (Kd) in excess of 180 microM. However, binding was observed in the presence of saturating ATP (200 microM), where 1 mol of tyrosine bound per mol of TyrR subunit with half-maximal saturation at 50 microM tyrosine. The binding exhibited positive cooperativity (nH of 1.2). There was no detectable binding of either phenylalanine or tryptophan to TyrR (40 microM) in the absence or presence of 200 microM ATP, indicating that any binding of these amino acids to TyrR or TyrR.ATP also has a Kd in excess of 180 microM. Each of these amino acids was found to inhibit the binding of tyrosine by TyrR.ATP when present in large molar excess (20 microM tyrosine and 2 or 10 mM phenylalanine or tryptophan), indicating that TyrR binds each of these amino acids, albeit more weakly than it binds tyrosine.

gamma-Tubulin in Arabidopsis: gene sequence, immunoblot, and immunofluorescence studies

gamma-Tubulin is a protein associated with microtubule (Mt)-organizing centers in a variety of eukaryotic cells. Unfortunately, little is known about such centers in plants. Genomic and partial cDNA clones encoding two gamma-tubulins of Arabidopsis were isolated and sequenced. Comparisons of genomic and cDNA sequences showed that both genes, TubG1 and TubG2, contain nine introns at conserved locations. The sequences of the two genes both predict proteins containing 474 amino acids, with molecular masses of 53,250 and 53,280 D, respectively. The predicted gamma 1- and gamma 2-tubulins exhibit 98% amino acid identity with each other and approximately 70% amino acid identity with the gamma-tubulins of animals and fungi. RNA gel blot results demonstrated that both genes are transcribed in suspension culture cells, seedlings, and roots and flowers of mature plants. Immunoblots of Arabidopsis proteins using an antibody specific to a conserved peptide of gamma-tubulin showed a major cross-reacting polypeptide with an M(r) of 58,000. The same antibody stained all Mt arrays in tissue and suspension culture cells of this species. Binding was inhibited by the homologous oligopeptide in the gamma-tubulins predicted by the two Arabidopsis gene sequences. Antibody staining avoided the plus ends of Mts at the kinetochores and cell plate, but unlike the case in animal cells, seemed to be localized over broad stretches of the kinetochore fibers and phragmoplast toward the minus ends. We concluded that at least two gamma-tubulin protein homologs are present in Arabidopsis and that at least one of them is localized along Mt arrays. Its distribution is correlated with and may help explain unique characteristics of Mt organization in plants.

Cultured fibroblasts in avian scleroderma, an autoimmune fibrotic disease, display an activated phenotype

University of California, Davis, line 200 and 206 chickens spontaneously develop an autoimmune syndrome that has many features analogous to human scleroderma, including dermal fibrosis, antinuclear antibodies and antibodies to type II collagen. These birds also have thymic subcapsular epithelial defects and an abnormality in T cell calcium influx and proliferation in response to both T cell receptor-dependent and -independent activators. To determine whether fibroblast activation is a contributing factor to development of skin fibrosis in line 200/206 chickens, as it is in human scleroderma, we studied the collagen, non-collagenous protein and glycosaminoglycan (GAG) production of 34 separate fibroblast lines derived from the normal and fibrotic skin of line 200 and 206 chickens and from the skin of control chicken lines 058 and 254. The mean +/- SEM 24-h incorporation of 3H-proline or 3H-glucosamine into extracellular collagen, non-collagenous protein or GAG by first passage fibroblast lines derived from the fibrotic skin of diseased birds was 1,526 +/- 136, 859 +/- 82 and 25.7 +/- 1.3 dpm/10(3) cells, respectively, while fibroblast lines derived from the skin of control birds produced only 341 +/- 36, 343 +/- 42 and 15.2 +/- 1.4 dpm/10(3) cells. Similar differences in results were recorded for cell-associated production, and when collagen and non-collagenous protein production were assessed using non-radioactive electrophoretic methods. The activated phenotype of the fibroblast lines derived from the fibrotic skin of diseased birds persisted through 10 cell doublings in tissue culture. However, the ratio of type I:III collagen and the profile of GAG types produced were similar in all fibroblast lines studied. These results suggest that fibroblast activation is responsible for the skin fibrosis observed in this avian model of scleroderma.

Avian scleroderma: evidence for qualitative and quantitative T cell defects

T cell activation is dependent upon calcium influx and protein kinase C activation, with subsequent lymphocyte proliferation dependent upon IL-2. Abnormalities in T cell proliferation, including abnormal calcium influx and defective protein kinase C activation, have been identified in aged mice and humans and many autoimmune diseases including diabetes, lupus and scleroderma. Since UCD line 200 chickens, which spontaneously develop a scleroderma-like disease, have both thymic defects and a diminished peripheral blood lymphocyte response to IL-2, we have further investigated T cell function in these birds. Interestingly, line 200 T cells respond poorly in vitro to a variety of diversely acting T cell mitogens including concanavalin A, phytohemagglutinin and anti-chicken CD3 monoclonal antibody. Moreover, they do not respond well even to phorbol myristate acetate in conjunction with ionomycin. Addition of exogenous IL-2-containing supernatant concurrently with mitogenic stimulation also had no significant effect. Analysis of intracellular free calcium demonstrated that the lymphocytes from diseased birds had a reduced influx of calcium (or release for intracellular stores) following stimulation. These data clearly reflect a unique defect in T cell activation associated with avian scleroderma. Analysis of chicken CD3, CD4 and CD8 expression revealed a 39% decrease in peripheral blood CD4+ cells in scleroderma birds, although this decrease was not sufficient to explain the 80-90% decrease observed in proliferation assays and calcium influx. Our data support the hypothesis that avian scleroderma is mediated via abnormal function of lymphocyte co-stimulatory molecules or intracellular calcium regulators.

The 14 kDa beta-galactoside binding lectin in myoblast and myotube cultures: localization by confocal microscopy

The endogenous 14 kDa beta-galactoside-specific lectin has been localised in myoblasts and myotubes by indirect immunofluorescence using confocal microscopy. The antibodies used in these experiments suggest that in myoblast cultures the lectin is abundant on the cell surface and concentrated at ruffled edges of migrating cells. The quantity and distribution of cell surface lectin is independent of the nature of the substratum and undiminished by brief trypsinisation or lactose-washing of the cell suspension. The lectin is also abundant intracellularly, apparently relatively free in the cytoplasm until the cells approach confluency, when the lectin is concentrated into particular areas of cytoplasm resulting in a ‘patchy’ appearance of stained cells. After fusion to form multinucleate myotubes, intracellular lectin is less abundant and concentrated at the periphery of myotubes, from where lectin appears to be released in vesicles packed with lectin which ‘bud off’ from the myotube surface. In recolonising cultures, lectin is apparently more abundant and lectin-packed vesicles can also be seen ‘budding off’ from myoblasts. In differentiated cultures, extracellular lectin is detected both on the myotube surface and in fibrillar arrays of extracellular material.