Defining the condensate landscape of fusion oncoproteins

Fusion oncoproteins (FOs) arise from chromosomal translocations in ~17% of cancers and are often oncogenic drivers. Although some FOs can promote oncogenesis by undergoing liquid-liquid phase separation (LLPS) to form aberrant biomolecular condensates, the generality of this phenomenon is unknown. We explored this question by testing 166 FOs in HeLa cells and found that 58% formed condensates. The condensate-forming FOs displayed physicochemical features distinct from those of condensate-negative FOs and segregated into distinct feature-based groups that aligned with their sub-cellular localization and biological function. Using Machine Learning, we developed a predictor of FO condensation behavior, and discovered that 67% of ~3000 additional FOs likely form condensates, with 35% of those predicted to function by altering gene expression. 47% of the predicted condensate-negative FOs were associated with cell signaling functions, suggesting a functional dichotomy between condensate-positive and -negative FOs. Our Datasets and reagents are rich resources to interrogate FO condensation in the future.

Phase Separation Mediates NUP98 Fusion Oncoprotein Leukemic Transformation

NUP98 fusion oncoproteins (FO) are drivers in pediatric leukemias and many transform hematopoietic cells. Most NUP98 FOs harbor an intrinsically disordered region from NUP98 that is prone to liquid-liquid phase separation (LLPS) in vitro. A predominant class of NUP98 FOs, including NUP98-HOXA9 (NHA9), retains a DNA-binding homeodomain, whereas others harbor other types of DNA- or chromatin-binding domains. NUP98 FOs have long been known to form puncta, but long-standing questions are how nuclear puncta form and how they drive leukemogenesis. Here we studied NHA9 condensates and show that homotypic interactions and different types of heterotypic interactions are required to form nuclear puncta, which are associated with aberrant transcriptional activity and transformation of hematopoietic stem and progenitor cells. We also show that three additional leukemia-associated NUP98 FOs (NUP98-PRRX1, NUP98-KDM5A, and NUP98-LNP1) form nuclear puncta and transform hematopoietic cells. These findings indicate that LLPS is critical for leukemogenesis by NUP98 FOs.

SIGNIFICANCE

We show that homotypic and heterotypic mechanisms of LLPS control NUP98-HOXA9 puncta formation, modulating transcriptional activity and transforming hematopoietic cells. Importantly, these mechanisms are generalizable to other NUP98 FOs that share similar domain structures. These findings address long-standing questions on how nuclear puncta form and their link to leukemogenesis. This article is highlighted in the In This Issue feature, p. 873.

C9orf72 Poly(PR) Dipeptide Repeats Disturb Biomolecular Phase Separation and Disrupt Nucleolar Function

Repeat expansion in the C9orf72 gene is the most common cause of the neurodegenerative disorder amyotrophic lateral sclerosis (C9-ALS) and is linked to the unconventional translation of five dipeptide-repeat polypeptides (DPRs). The two enriched in arginine, poly(GR) and poly(PR), infiltrate liquid-like nucleoli, co-localize with the nucleolar protein nucleophosmin (NPM1), and alter the phase separation behavior of NPM1 in vitro. Here, we show that poly(PR) DPRs bind tightly to a long acidic tract within the intrinsically disordered region of NPM1, altering its phase separation with nucleolar partners to the extreme of forming large, soluble complexes that cause droplet dissolution in vitro. In cells, poly(PR) DPRs disperse NPM1 from nucleoli and entrap rRNA in static condensates in a DPR-length-dependent manner. We propose that R-rich DPR toxicity involves disrupting the role of phase separation by NPM1 in organizing ribosomal proteins and RNAs within the nucleolus.

Methods for Physical Characterization of Phase-Separated Bodies and Membrane-less Organelles

Membrane-less organelles are cellular structures which arise through the phenomenon of phase separation. This process enables compartmentalization of specific sets of macromolecules (e.g., proteins, nucleic acids), thereby regulating cellular processes by increasing local concentration, and modulating the structure and dynamics of their constituents. Understanding the connection between structure, material properties and function of membrane-less organelles requires inter-disciplinary approaches, which address length and timescales that span several orders of magnitude (e.g., Ångstroms to micrometer, picoseconds to hours). In this review, we discuss the wide variety of methods that have been applied to characterize the morphology, rheology, structure and dynamics of membrane-less organelles and their components, in vitro and in live cells.

Selection Signatures Underlying Dramatic Male Inflorescence Transformation During Modern Hybrid Maize Breeding

Inflorescence capacity plays a crucial role in reproductive fitness in plants, and in production of hybrid crops. Maize is a monoecious species bearing separate male and female flowers (tassel and ear, respectively). The switch from open-pollinated populations of maize to hybrid-based breeding schemes in the early 20th century was accompanied by a dramatic reduction in tassel size, and the trend has continued with modern breeding over the recent decades. The goal of this study was to identify selection signatures in genes that may underlie this dramatic transformation. Using a population of 942 diverse inbred maize accessions and a nested association mapping population comprising three 200-line biparental populations, we measured 15 tassel morphological characteristics by manual and image-based methods. Genome-wide association studies identified 242 single nucleotide polymorphisms significantly associated with measured traits. We compared 41 unselected lines from the Iowa Stiff Stalk Synthetic (BSSS) population to 21 highly selected lines developed by modern commercial breeding programs, and found that tassel size and weight were reduced significantly. We assayed genetic differences between the two groups using three selection statistics: cross population extended haplotype homozogysity, cross-population composite likelihood ratio, and fixation index. All three statistics show evidence of selection at genomic regions associated with tassel morphology relative to genome-wide null distributions. These results support the tremendous effect, both phenotypic and genotypic, that selection has had on maize male inflorescence morphology.

Genotype-by-environment interactions affecting heterosis in maize

The environment can influence heterosis, the phenomena in which the offspring of two inbred parents exhibits phenotypic performance beyond the inbred parents for specific traits. In this study we measured 25 traits in a set of 47 maize hybrids and their inbred parents grown in 16 different environments with varying levels of average productivity. By quantifying 25 vegetative and reproductive traits across the life cycle we were able to analyze interactions between the environment and multiple distinct instances of heterosis. The magnitude and rank among hybrids for better-parent heterosis (BPH) varied for the different traits and environments. Across the traits, a higher within plot variance was observed for inbred lines compared to hybrids. However, for most traits, variance across environments was not significantly different for inbred lines compared to hybrids. Further, for many traits the correlations of BPH to hybrid performance and BPH to better parent performance were of comparable magnitude. These results indicate that inbred lines and hybrids show similar trends in environmental response and both are contributing to observed genotype-by-environment interactions for heterosis. This study highlights the degree of heterosis is not an inherent trait of a specific hybrid, but varies depending on the trait measured and the environment where that trait is measured. Studies that attempt to correlate molecular processes with heterosis are hindered by the fact that heterosis is not a consistent attribute of a specific hybrid.

The intervertebral disc contains intrinsic circadian clocks that are regulated by age and cytokines and linked to degeneration

OBJECTIVES

The circadian clocks are internal timing mechanisms that drive ∼24-hour rhythms in a tissue-specific manner. Many aspects of the physiology of the intervertebral disc (IVD) show clear diurnal rhythms. However, it is unknown whether IVD tissue contains functional circadian clocks and if so, how their dysregulation is implicated in IVD degeneration.

METHODS

Clock gene dynamics in ex vivo IVD explants (from PER2:: luciferase (LUC) reporter mice) and human disc cells (transduced with lentivirus containing Per2::luc reporters) were monitored in real time by bioluminescence photon counting and imaging. Temporal gene expression changes were studied by RNAseq and quantitative reverse transcription (qRT)-PCR. IVD pathology was evaluated by histology in a mouse model with tissue-specific deletion of the core clock gene Bmal1.

RESULTS

Here we show the existence of the circadian rhythm in mouse IVD tissue and human disc cells. This rhythm is dampened with ageing in mice and can be abolished by treatment with interleukin-1β but not tumour necrosis factor α. Time-series RNAseq revealed 607 genes with 24-hour patterns of expression representing several essential pathways in IVD physiology. Mice with conditional knockout of Bmal1 in their disc cells demonstrated age-related degeneration of IVDs.

CONCLUSIONS

We have established autonomous circadian clocks in mouse and human IVD cells which respond to age and cytokines, and control key pathways involved in the homeostasis of IVDs. Genetic disruption to the mouse IVD molecular clock predisposes to IVD degeneration. These results support the concept that disruptions to circadian rhythms may be a risk factor for degenerative IVD disease and low back pain.

Primitive Neuroectodermal Neoplasia in Coho Salmon, Oncorhynchus kisutch

Twelve coho salmon, approximately 8 weeks old, were each observed to have a single neoplasm involving the dorsolateral axial skeletal musculature. The neoplasm was closely associated with the vertebrae in all cases. The neoplasm was composed of islands containing small cells with round and occasional spindeloid morphology. Neoplastic cells had basophilic cytoplasm and vesicular nuclei. These cells exhibited immunopositivity only for vimentin and S-100 protein. Ultrastructurally, neoplastic cells had nuclei with a predominance of euchromatin, cytoplasm containing marked amounts of rough endoplasmic reticulum, scant amounts of smooth endoplasmic reticulum, and scattered mitochondria. Rudimentary cell junctions were occasionally observed between adjacent neoplastic cells. Based on the close association of these neoplasms with the vertebrae as well as the histologic, ultrastructural, and immunohistochemical findings, these neoplasms were considered to all be primitive neuroectodermal neoplasms.

The sweet side of RNA regulation: glyceraldehyde-3-phosphate dehydrogenase as a noncanonical RNA-binding protein

The glycolytic protein, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), has a vast array of extraglycolytic cellular functions, including interactions with nucleic acids. GAPDH has been implicated in the translocation of transfer RNA (tRNA), the regulation of cellular messenger RNA (mRNA) stability and translation, as well as the regulation of replication and gene expression of many single-stranded RNA viruses. A growing body of evidence supports GAPDH-RNA interactions serving as part of a larger coordination between intermediary metabolism and RNA biogenesis. Despite the established role of GAPDH in nucleic acid regulation, it is still unclear how and where GAPDH binds to its RNA targets, highlighted by the absence of any conserved RNA-binding sequences. This review will summarize our current understanding of GAPDH-mediated regulation of RNA function. WIREs RNA 2016, 7:53-70. doi: 10.1002/wrna.1315 For further resources related to this article, please visit the WIREs website.

Small-angle X-ray scattering method to characterize molecular interactions: Proof of concept

Characterizing biomolecular interactions is crucial to the understanding of biological processes. Existing characterization methods have low spatial resolution, poor specificity, and some lack the capability for deep tissue imaging. We describe a novel technique that relies on small-angle X-ray scattering signatures from high-contrast molecular probes that correlate with the presence of biomolecular interactions. We describe a proof-of-concept study that uses a model system consisting of mixtures of monomer solutions of gold nanoparticles (GNPs) as the non-interacting species and solutions of GNP dimers linked with an organic molecule (dimethyl suberimidate) as the interacting species. We report estimates of the interaction fraction obtained with the proposed small-angle X-ray scattering characterization method exhibiting strong correlation with the known relative concentration of interacting and non-interacting species.

A dimer interface mutation in glyceraldehyde-3-phosphate dehydrogenase regulates its binding to AU-rich RNA

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is an enzyme best known for its role in glycolysis. However, extra-glycolytic functions of GAPDH have been described, including regulation of protein expression via RNA binding. GAPDH binds to numerous adenine-uridine rich elements (AREs) from various mRNA 3'-untranslated regions in vitro and in vivo despite its lack of a canonical RNA binding motif. How GAPDH binds to these AREs is still unknown. Here we discovered that GAPDH binds with high affinity to the core ARE from tumor necrosis factor-α mRNA via a two-step binding mechanism. We demonstrate that a mutation at the GAPDH dimer interface impairs formation of the second RNA-GAPDH complex and leads to changes in the RNA structure. We investigated the effect of this interfacial mutation on GAPDH oligomerization by crystallography, small-angle x-ray scattering, nano-electrospray ionization native mass spectrometry, and hydrogen-deuterium exchange mass spectrometry. We show that the mutation does not significantly affect GAPDH tetramerization as previously proposed. Instead, the mutation promotes short-range and long-range dynamic changes in regions located at the dimer and tetramer interface and in the NAD(+) binding site. These dynamic changes are localized along the P axis of the GAPDH tetramer, suggesting that this region is important for RNA binding. Based on our results, we propose a model for sequential GAPDH binding to RNA via residues located at the dimer and tetramer interfaces.

Linear alkaline earth metal phosphinate coordination polymers: synthesis and structural characterization

Reaction of alkaline earth metal salts with diphenylphosphinic acid in dimethylformamide solvent afforded four coordination polymers: [Mg3(O2PPh2)6(DMF)2]·2DMF (I), [Ca(O2PPh2)2(DMF)2] (II), [Sr(O2PPh2)2(DMF)2] (III) and [Ba(O2PPh2)2(DMF)2] (IV) (where DMF is N,N-dimethylformamide). Single-crystal X-ray diffraction revealed that all four compounds produce linear chain structures in the solid state, with the Ca, Sr and Ba forming isostructural crystals. The bulk materials were characterized by FT-IR and (1)H NMR spectroscopy and elemental analyses.

Increasing antiviral activity of surfactant protein d trimers by introducing residues from bovine serum collectins: dissociation of mannan-binding and antiviral activity

Collectins contribute to host defence through interactions with glycoconjugates on pathogen surfaces. We have prepared recombinant trimeric neck and carbohydrate recognition domains (NCRD) of collectins, and we now show that the NCRD of bovine conglutinin and CL-46 (like that of CL-43) have greater intrinsic antiviral activity for influenza A virus (IAV) than the human SP-D NCRD (hSP-D-NCRD). The three serum collectins differ from SP-D by having insertions adjacent to amino acid 325 and substitution of hydrophobic residues for arginine 343. We previously showed that a three amino acid (RAK) insertion, as found in CL-43, increases antiviral activity and mannan-binding activity of the hSP-D-NCRD, while the substitution of valine at 343, as in conglutinin, more strongly increased these activities. Mannan-binding activity of collectins has been considered to predict for ability to bind to high mannose glycans on viruses or other pathogens. We now show, however, that combined mutants containing the RAK insertion and R343V or R343I substitutions have greatly increased mannan-binding ability, but lower IAV binding or inhibiting activity than mutants containing R343V or R343I substitutions only. These findings indicate differences in the recognition of glycan structures of mannan and IAV by the NCRD and emphasize the importance of the flanking sequences in determining the differing interactions of human SP-D and bovine serum collectins with mannose-rich glycoconjugates on IAV and other pathogens. Of interest, we show conservation of some monoclonal antibody-binding epitopes between bovine collectin NCRD and hSP-D, suggesting shared structural motifs.

Multiple components contribute to ability of saliva to inhibit influenza viruses

INTRODUCTION

Saliva is a potentially important barrier against respiratory viral infection but its mechanism of action is not well studied.

METHODS

We tested the antiviral activities of whole saliva, specific salivary gland secretions, and purified salivary proteins against strains of influenza A virus (IAV) in vitro.

RESULTS

Whole saliva or parotid or submandibular/sublingual secretions from healthy donors inhibited IAV based on hemagglutination inhibition and neutralization assays. This differs from human immunodeficiency virus (HIV), for which only submandibular/sublingual secretions are reported to be inhibitory. Among purified salivary proteins, MUC5B, scavenger receptor cysteine-rich glycoprotein 340 (salivary gp-340), histatins, and human neutrophil defensins (HNPs) inhibited IAV at the concentrations present in whole saliva. In contrast, some abundant salivary proteins (acidic proline-rich proteins and amylase) had no activity, nor did several other less abundant salivary proteins with known activity against HIV (e.g. thrombospondin or serum leukocyte protease inhibitor). Whole saliva and MUC5B did not inhibit neuraminidase activity of IAV and viral neutralizing and aggregating activity of MUC5B was potentiated by the neuraminidase inhibitor oseltamivir. Hence, MUC5B inhibits IAV by presenting a sialic acid ligand for the viral hemagglutinin. The mechanism of action of histatins requires further study.

CONCLUSIONS

These findings indicate that saliva represents an important initial barrier to IAV infection and underline the complexity of host defense activity of oral secretions. Of interest, antiviral activity of saliva against IAV and HIV differs in terms of specific glandular secretions and proteins that are inhibitory.

Inhibition of influenza viral neuraminidase activity by collectins

The collectins, lung surfactant proteins A and D (SP-A and SP-D), contribute to innate host defense against influenza A virus (IAV) in vivo. Although collectins bind to the viral hemagglutinin (HA) and inhibit early stages of viral infection in vitro, they also bind to the neuraminidase (NA) and inhibit NA activity. We used a variety of NA functional assays, viral strains and recombinant (mutant or wild type) collectins to characterize the mechanism of NA inhibition. NA inhibition by SP-D correlates with binding of its carbohydrate recognition domain (CRD) to oligomannose oligosaccharides on the viral hemagglutinin (HA). The effects of SP-D are additive with oseltamivir, consistent with differences in mechanism of action. NA inhibition was observed using fetuin or MDCK cells as a substrate, but not in assays using a soluble sialic acid analogue. Collectin multimerization and CRD binding properties are key determinants for NA inhibition. SP-D had greater NA inhibitory activity than mannose-binding lectin, which in turn had greater activity than SP-A. The markedly greater NA inhibitory activity of SP-D compared to SP-A may partly account for the finding that deletion of the SP-D gene in mice has a greater effect on viral replication in vivo.

Influenza A Viruses Upregulate Neutrophil Toll-Like Receptor 2 Expression and Function

Neutrophils are involved in the initial host response to influenza A virus (IAV) infection and exhibit both activation and depressed function after exposure to the virus. We demonstrate that IAV causes rapid upregulation of Toll-like receptor 2 (TLR2) expression on neutrophils. The neutrophil agonists, formyl-methylpleucyl-alanine (fMLP), C5a and lipopolysaccharide did not alter neutrophil TLR2 expression, whereas PMA and the microbial TLR2 ligands, peptidoglycan (PGN) and zymosan, reduced it. To determine the functional significance of IAV-induced increase in TLR2 expression, IAV-treated neutrophils were exposed to PGN, Staphylococcus aureus (S. aureus) and zymosan. Pretreatment with IAV resulted in significantly increased uptake of S. aureus and zymosan and accelerated neutrophil apoptosis when combined with S. aureus. IAV-treated cells generated significantly more H(2)O(2) in response to PGN. These results indicate that IAV increases neutrophil surface expression of TLR2 and modulates functional responses to ligands that bind TLR2. These findings may clarify IAV-induced perturbation of neutrophil functions in vivo.

Evaluation of nested polymerase chain reaction, pepsin/trypsin digest, and histology for the detection of Myxobolus cerebralis in salmonid fishes of Indiana and Michigan

The objectives of this study were to survey fish from state hatcheries in Indiana and Michigan and to compare the nested polymerase chain reaction (PCR) test with pepsin/trypsin digest (PTD) and histopathology for the diagnosis of whirling disease (WD). One group of 40 and 9 groups of 60 fish heads, for a total of 580 samples, were submitted from hatcheries in Indiana and Michigan. These samples were examined for myxozoan spores using histopathology, PTD, and PCR tests. The heads were hemisectioned, and one half was fixed in 10% neutral-buffered formalin for histopathologic examination. The other half was processed for PTD. Some of the sediment was examined for the presence of myxozoan spores, and the rest was prepared for the nested PCR. Histologic examinations did not reveal Myxobolus cerebralis in any of the 580 samples. One hundred serial step sections, taken at 5-microm intervals, were evaluated for samples with positive spore identification by PTD. Histologic examination of these sections failed to reveal any myxozoan parasites. Myxozoan spores were observed in 16.9% (98/580) of samples in sediment after PTD. Spores morphologically similar to those of M. cerebralis were observed in 1.0% of PTD samples (n = 6). The nested PCR indicated that M. cerebralis spores were present in 0.5% of samples (n = 3). All 3 nested PCR-positive samples came from the same hatchery, however, spores of M. cerebralis were seen in 1 sample, spores of other myxozoan species were seen in the second sample, and spores were not seen in the third sample. When comparing the PTD to the nested PCR test, the PTD diagnosed 1 true positive, 5 false positives, 2 false negatives, and 572 true negatives, for a sensitivity of 33% and a specificity of 99.1%. Screening for M. cerebrallis infection in this study indicated a low prevalence of the disease. Histopathology was a very insensitive indicator of WD. The PCR test was highly specific and was used to differentiate spores of M. cerebralis from similar spores of other species.

Hyperadrenocorticism associated with excessive sex hormone production by an adrenocortical tumor in two dogs

An 11-year-old spayed female Labrador Retriever and a 9-year-old castrated male miniature Poodle were evaluated because of clinical signs of hyperadrenocorticism. Cortisol testing did not support a diagnosis of hypercortisolemia in either dog; however, imaging studies revealed unilateral adrenal tumors in both dogs. Serum concentrations of 17-hydroxyprogesterone, progesterone, and estradiol were high in both dogs, and androstenedione concentrations were also high in 1 dog. It is suspected that sex hormone secretion by the adrenal tumors in these dogs resulted in clinical signs of hyperadrenocorticism. Clinical signs and hormonal abnormalities resolved in the male dog after surgical resection of the tumor. There was no improvement in clinical signs after treatment with mitotane in the female dog, which died 2 months after diagnosis. Histologic evaluation confirmed the presence of adrenocortical carcinoma in both dogs.

BCL-2 family expression in human neutrophils during delayed and accelerated apoptosis

The human neutrophil spontaneously undergoes apoptosis, but this type of cell death can be delayed or accelerated by a wide variety of agents. There are wide discrepancies in the literature regarding the expression of the Bcl-2 family of proteins in human neutrophils. Here, we show that A1, Mcl-1, Bcl-X(L), and Bad are major transcripts in human neutrophils and that levels of these transcripts are cytokine regulated. However, no Bcl-X(L) protein was detected in Western blots. Protein levels for the proapoptotic proteins Bad, Bax, Bak, and Bik remained constant during culture, despite changes in the levels of mRNA for these gene products. These proapoptotic proteins were extremely stable, having very long half-lives. In contrast, A1 and Mcl-1 transcripts were extremely unstable (with approximately 3-h half-lives), and Mcl-1 protein was also subject to rapid turnover. These results indicate that neutrophil survival is regulated by the inducible expression of the short-lived Mcl-1 and possibly the A1 gene products. In the absence of their continued expression, these prosurvival gene products are rapidly turned over, and then the activity of the stable death proteins predominates and promotes apoptosis.

Characterization of the ethanol-inducible alc gene-expression system in Arabidopsis thaliana

Controlled expression of transgenes in plants is key to the characterization of gene function and the regulated manipulation of growth and development. The alc gene-expression system, derived from the filamentous fungus Aspergillus nidulans, has previously been used successfully in both tobacco and potato, and has potential for use in agriculture. Its value to fundamental research is largely dependent on its utility in Arabidopsis thaliana. We have undertaken a detailed function analysis of the alc regulon in A. thaliana. By linking the alcA promoter to beta-glucuronidase (GUS), luciferase (LUC) and green fluorescent protein (GFP) genes, we demonstrate that alcR-mediated expression occurs throughout the plant in a highly responsive manner. Induction occurs within one hour and is dose-dependent, with negligible activity in the absence of the exogenous inducer for soil-grown plants. Direct application of ethanol or exposure of whole plants to ethanol vapour are equally effective means of induction. Maximal expression using soil-grown plants occurred after 5 days of induction. In the majority of transgenics, expression is tightly regulated and reversible. We describe optimal strategies for utilizing the alc system in A. thaliana.

Increased antiviral and opsonic activity of a highly multimerized collectin chimera

Altering the carbohydrate binding properties of surfactant protein D (SP-D) [e.g., by replacing its carbohydrate recognition domain (CRD) with that of either mannose binding lectin (MBL) or conglutinin] can increase its activity against influenza A virus (IAV). The current study demonstrates that the degree of multimerization of SP-D is another independent determinant of antiviral activity. A chimeric collectin containing the N-terminus and collagen domain of human SP-D and the CRD of MBL formed high-molecular-weight multimers similar to those previously described for human SP-D. Using several complementary assays, and diverse viral strains, the chimeric multimers showed greater anti-IAV activity than similarly multimerized preparations of SP-D or incompletely oligomerized preparations of the chimera. More highly multimerized preparations of the chimera also caused greater increases in uptake of IAV by neutrophils. These studies may have implications for development of collectins as therapeutic agents and understanding of natural variations in susceptibility to IAV infection.

Persistent synchronized oscillations in prolactin gene promoter activity in living pituitary cells

PRL gene expression in the anterior pituitary gland responds rapidly to different hormonal signals. We have investigated the long-term timing of transcriptional activation from the PRL, GH, and cytomegalovirus promoters in response to different stimulus duration, using real-time imaging of luciferase expression in living stably transfected GH3 cells. Long-term stimulation of serum-starved cells with 50% serum induced a homogeneous rise in PRL promoter activity, with subsequent heterogeneous fluctuations in luciferase activity in individual cells. When cells were subjected to a 2-h pulse of 50% serum, followed by serum-free medium, there were long-term (approximately 50 h) synchronized, homogeneous oscillations in PRL promoter activity. This response was PRL-specific, because in GH3 cells expressing luciferase from the GH or cytomegalovirus promoters, a serum pulse elicited no oscillations in luciferase expression after an initial transient response to serum. The PRL promoter may therefore be a template for an unstable transcription complex subject to stochastic regulation, allowing an oscillatory transcriptional response to physiological signals. This suggests that precise timing and coordination of cell responses to different signal-duration may represent a novel mechanism for coordinating long-term dynamic changes in transcription in cell populations.

Precursor cystatin C in cultured retinal pigment epithelium cells: evidence for processing through the secretory pathway

Evidence was recently reported that the cysteine proteinase inhibitor, cystatin C, is highly expressed by cultured human retinal pigment epithelial (RPE) cells. As a step towards understanding possible functions of this protein associated with the RPE, the localization, targetting and trafficking of cystatin C were investigated. Constructs encoding an enhanced variant of green fluorescent protein (EGFP) fused to precursor cystatin C and to mature cystatin C were made and transfected into cultured human RPE cells. Expression of fusion proteins was monitored in vivo by fluorescence confocal microscopy. In cells transfected with precursor cystatin C-EGFP, fluorescence was initially targetted to the perinuclear zone, co-localizing with the Golgi apparatus. Transfected cells were observed at intervals over a period of up to 3 weeks, during which time fluorescent vesicles developed peripherally and basally while fluorescence continued to be detected in the Golgi region. Immunochemical analysis of cell lysates confirmed the expression of a fusion protein recognized by antibodies to both cystatin C and EGFP. Cells transfected with the construct lacking the leader peptide of precursor cystatin C presented a diffuse and weak fluorescence. Together, these results imply a leader sequence-dependent processing of cystatin C through the secretory pathway of RPE cells. This was confirmed by the detection, by Western blotting, of the chimaeric protein alongside endogenous cystatin C in the medium of transfected RPE cells.

Transcription inhibition induced by modified triple helix-forming oligonucleotides: a quantitative assay for evaluation in cells

Oligonucleotides can bind to double-stranded DNA in a sequence-specific manner to form triple helices. Uniformly modified, pyrimidine-rich oligodeoxyribonuclotides containing internucleosidic N3'-P5' phosphoramidate linkages are known to form very stable triplexes with their DNA target. Psoralen-conjugated triple helix-forming oligonucleotides (Pso-TFOs) can additionally be photo-induced to become irreversibly bound to their targeted DNA sequence. Here, we have examined the ability of various 15-mer phosphoramidate TFOs targeted to the HIV-1 polypurine tract (PPT) sequence to prevent transcription elongation in cell cultures; the PPT sequence has been cloned in the transcribed region of a reporter firefly luciferase gene (luc) and transient expression experiments performed. We show that the level of transcription inhibition of the reporter gene in cells perfectly correlates with the amount of covalent triplex at the PPT site. The efficacy of non-covalent triplexes (either omitting the irradiation step with the psoralen conjugate, or using the unsubstituted oligonucleotide) has been studied in our expression system; the oligonucleotides were introduced into living cells by cationic lipid-mediated delivery or directly into the cell nucleus by microinjection. This experimental approach allowed us to evaluate the intrinsic activity of triplexes as transcriptional inhibitors; transcription elongation was inhibited in cells in a sequence-dependent and concentration-dependent manner. This experimental system is convenient for quantitative and fast evaluation of new chemistries of antigene oligonucleotides as inhibitors of gene expression in cells and in vivo.

Photoperiodic regulation of prolactin gene expression in the Syrian hamster by a pars tuberalis-derived factor

Syrian hamsters exhibit a marked seasonal variation in prolactin secretion. The aim of this study was to analyse the nature of the photoperiodic regulation of prolactin gene expression, and to define the role of melatonin and the pars tuberalis of the anterior pituitary in this process. Pituitary prolactin gene expression, restricted to the pars distalis, was increased in hamsters maintained in long daylengths (16 h : 8 h, light : dark) compared to hamsters exposed to short daylengths (8 h : 16 h, light : dark) for 8-12 weeks. Analysis of single cells by in situ hybridization showed that photoperiod had no effect on the percentage of pars distalis cells expressing prolactin mRNA, but shifted the frequency distribution of prolactin mRNA expression per cell, such that in long photoperiods a greater proportion of cells were recruited to a higher expressing population. In vitro coculture of hamster pars tuberalis fragments increased prolactin promoter-driven luciferase activity in stably transfected GH3 cells in a dose- and duration-dependent manner. Conditioned medium from hamster and ovine pars tuberalis also activated the prolactin promoter. Furthermore, basal and forskolin-stimulated conditioned medium from hamster pars tuberalis increased prolactin mRNA expression in primary cultures of pars distalis cells. Melatonin attenuated the activity of pars tuberalis-conditioned medium but had no direct effect on either prolactin mRNA expression or secretion in pars distalis cell cultures. Finally, pars tuberalis fragments from long photoperiod hamsters stimulated prolactin gene promoter activity to a greater extent than those from short photoperiod hamsters. In conclusion, this study provides the first evidence in a seasonal mammal that the synthesis of prolactin depends on photoperiodic modulation of a pars tuberalis-derived factor. Our data support further the hypothesis that seasonal modulation of prolactin gene expression depends upon a melatonin-dependent paracrine action of the pars tuberalis on pars distalis lactotrophic cells.

Phosphoramidate oligonucleotides as potent antisense molecules in cells and in vivo

Antisense oligonucleotides are designed to specifically hybridize to a target messenger RNA (mRNA) and interfere with the synthesis of the encoded protein. Uniformly modified oligonucleotides containing N3'-P5' phosphoramidate linkages exhibit (NP) extremely high-affinity binding to single-stranded RNA, do not induce RNase H activity, and are resistant to cellular nucleases. In the present work, we demonstrate that phosphoramidate oligonucleotides are effective at inhibiting gene expression at the mRNA level, by binding to their complementary target present in the 5'-untranslated region. Their mechanism of action was demonstrated by comparative analysis of three expression systems that differ only by the composition of the oligonucleotide target sequence (HIV-1 polypurine tract or PPT sequence) present just upstream from the AUG codon of the firefly luciferase reporter gene: the experiments have been done on isolated cells using oligonucleotide delivery mediated by cationic molecules or streptolysin O (SLO), and in vivo by oligonucleotide electrotransfer to skeletal muscle. In our experimental system phosphoramidate oligonucleotides act as potent and specific antisense agents by steric blocking of translation initiation; they may prove useful to modulate RNA metabolism while maintaining RNA integrity.

Mechanism of binding of surfactant protein D to influenza A viruses: importance of binding to haemagglutinin to antiviral activity

Collectins are important in the initial containment of a variety of pathogens, including influenza A virus (IAV). We provide the first systematic evaluation of the oligosaccharide-binding sites for pulmonary surfactant protein D (SP-D) on specific IAV coat glycoproteins and define the relationship between this binding and antiviral activity. With the use of several techniques, SP-D was found to bind via its carbohydrate-recognition domain (CRD) to mannosylated, N-linked carbohydrates on the HA(1) domain of the haemagglutinin (HA) and on the neuraminidase of IAV. Using a set of IAV strains that differed in the level and site of glycosylation, and a panel of recombinant collectins, we found that binding of SP-D to the globular domain of the HA was critical in mediating the inhibition of viral haemagglutination activity and infectivity. We also demonstrated that the pattern of binding of a collectin to IAV glycoproteins can be modified by altering the monosaccharide-binding affinity of its CRD or by linking the CRD to a different N-terminal/collagen domain. These studies clarify the mechanisms of viral neutralization by collectins and might be useful in engineering collectins for enhanced antiviral activity.

Apoptosis is rapidly triggered by antisense depletion of MCL-1 in differentiating U937 cells

Mcl-1 is a member of the Bcl-2 protein family, which has been shown to delay apoptosis in transfection and/or overexpression experiments. As yet no gene knockout mice have been engineered, and so there is little evidence to show that loss of Mcl-1 expression is sufficient to trigger apoptosis. U937 cells constitutively express the antiapoptotic protein Bcl-2; but during differentiation, in response to the phorbol ester PMA (phorbol 12 beta-myristate 13 alpha-acetate), Mcl-1 is transiently induced. The purpose of this investigation was to determine the functional role played by Mcl-1 in this differentiation program. Mcl-1 expression was specifically disrupted by chimeric methylphosphonate/phosphodiester antisense oligodeoxynucleotides to just 5% of control levels. The depletion of Mcl-1 messenger RNA (mRNA) and protein was both rapid and specific, as indicated by the use of control oligodeoxynucleotides and analysis of the expression of other BCL2 family members and PMA-induced tumor necrosis factor-alpha (TNF-alpha). Specific depletion of Mcl-1 mRNA and protein, in the absence of changes in cellular levels of Bcl-2, results in a rapid entry into apoptosis. Levels of the proapoptotic protein Bax remained unchanged during differentiation, while Bak expression doubled within 24 hours. Apoptosis was detected within 4 hours of Mcl-1 antisense treatment by a variety of parameters including a novel live cell imaging technique allowing correlation of antisense treatment and apoptosis in individual cells. The induction of Mcl-1 is required to prevent apoptosis during differentiation of U937 cells, and the constitutive expression of Bcl-2 is unable to compensate for the loss of Mcl-1. (Blood. 2000;96:1756-1763)

Enhanced antiviral and opsonic activity of a human mannose-binding lectin and surfactant protein D chimera

The carbohydrate recognition domains (CRDs) of human serum mannose-binding lectin (MBL) and pulmonary surfactant protein D (SP-D) have distinctive monosaccharide-binding properties, and their N-terminal and collagen domains have very different quaternary structures. We produced a chimeric protein containing the N terminus and collagen domain of human SP-D and the neck region and CRD of human MBL (SP-D/MBLneck+CRD) to create a novel human collectin. The chimera bound to influenza A virus (IAV), inhibited IAV hemagglutination activity and infectivity, and induced aggregation of viral particles to a much greater extent than MBL. Furthermore, SP-D/MBLneck+CRD caused much greater increases in neutrophil uptake of, and respiratory burst responses to, IAV than MBL. These results indicate that pathogen interactions mediated by the MBL CRD are strongly influenced by the N-terminal and collagen-domain backbone to which it is attached. The presence of the CRD of MBL in the chimera resulted in altered monosaccharide binding properties compared with SP-D. As a result, the chimera caused greater aggregation and neutralization of IAV than SP-D. Distinctive functional properties of collectin collagenous domains and CRDs can be exploited to generate novel human collectins with potential for therapy of influenza.

In vivo localisation and stability of human Mcl-1 using green fluorescent protein (GFP) fusion proteins

Mcl-1 is an anti-apoptotic member of the Bcl-2 family of proteins. We have expressed full length and mutated GFP:Mcl-1 fusion proteins to define structural motifs that control protein localisation and stability. When expressed in U-937 cells, full length Mcl-1 locates primarily within mitochondria and its half-life was approximately 3 h, which was identical to the native, endogenously expressed protein. When the terminal 20 amino acids from the C-terminus of the protein were detected, the protein was diffused in the cytoplasm, but its stability was unaffected. This confirms that this region is responsible for efficient targeting to mitochondria. Surprisingly, deletion of 104 amino acids (residues 79-183) that contain putative PEST sequences and other stability regulating motifs, did not affect protein stability.

Interaction in vivo and in vitro of the metastasis-inducing S100 protein, S100A4 (p9Ka) with S100A1

The calcium-binding protein S100A4 (p9Ka) has been shown to cause a metastatic phenotype in rodent mammary tumor cells and in transgenic mouse model systems. mRNA for S100A4 (p9Ka) is present at a generally higher level in breast carcinoma than in benign breast tumor specimens, and the presence of immunocytochemically detected S100A4 correlates strongly with a poor prognosis for breast cancer patients. Recombinant S100A4 (p9Ka) has been reported to interact in vitro with cytoskeletal components and to form oligomers, particularly homodimers in vitro. Using the yeast two-hybrid system, a strong interaction between S100A4 (p9Ka) and another S100 protein, S100A1, was detected. Site-directed mutagenesis of conserved amino acid residues involved in the dimerization of S100 proteins abolished the interactions. The interaction between S100A4 and S100A1 was also observed in vitro using affinity column chromatography and gel overlay techniques. Both S100A1 and S100A4 can occur in the same cultured mammary cells, suggesting that in cells containing both proteins, S100A1 might modulate the metastasis-inducing capability of S100A4.

Targeted inhibition of transcription elongation in cells mediated by triplex-forming oligonucleotides

Triple-helix-forming oligonucleotides (TFOs) bind in the major groove of double-stranded DNA at oligopyrimidine small middle dotoligopurine sequences and therefore are candidate molecules for artificial gene regulation, in vitro and in vivo. We recently have described oligonucleotide analogues containing N3'-P5' phosphoramidate (np) linkages that exhibited efficient inhibition of transcription elongation in vitro. In the present work we provide conclusive evidence that np-modified TFOs targeted to the HIV-1 polypurine tract (PPT) sequence can inhibit transcriptional elongation in cells, either in transient or stable expression systems. The same constructs were used in transient expression assays (target sequence on transfected plasmid) and in the generation of stable cell lines (target sequence integrated into cellular chromosomes). In both cases the only distinguishable feature between the cellular systems is the presence of an insert containing the wild-type PPT/HIV-1 sequence, a mutated version with two mismatches, or the absence of the insert altogether. The inhibitory action induced by np-TFOs was restricted to the cellular systems containing the complementary wild-type PPT/HIV-1 target, and consequently can be attributed only to a triple-helix-mediated mechanism. As a part of this study we also have applied an imaging technique to quantitatively investigate the dynamics of TFO-mediated specific gene silencing in single cells.

Functional analysis of the human MCL-1 gene

We have isolated a 6.5-kb human genomic fragment that encodes the MCL-1 gene. Comparison of the coding region with the published full-length cDNA reveals that the gene contains three exons and two introns, and that our clone contains 370 bp of the 3'-untranslated region. We have mapped a major transcriptional start site to 80 residues upstream of the translation initiation codon. Reporter gene assays indicate that regulatory sequences responsible for phorbol ester (PMA)-stimulated activity and granulocyte-macrophage-colony-stimulating factor (GM-CSF)-stimulated activity were located within the first 294 bp of the 5'-flanking region upstream from the transcription start site. A deletion mutant was generated that lacked 47 bp between residues --215 and -- 168: in this mutant, six out of seven GGCCCC repeats and two GCTCA repeats were deleted. Serum-stimulated and GM-CSF-stimulated reporter activity were greatly decreased in this deletion mutant and PMA-stimulated activity was slightly decreased. While the coding and 3'-untranslated regions of the human and mouse genes have significant sequence similarity, there was very little sequence similarity in the 5'-flanking regions of the genes from these two species. Nevertheless, some consensus sequences for a number of transcription-factor-binding sites were detected in the two genes, indicating that transcription may be regulated by similar signalling pathways in these different species.

Choline is required by tilapia when methionine is not in excess

Choline is essential in diets fed to most young vertebrates, but previous studies did not confirm the essentiality of choline in diets fed to tilapia. Two experiments were conducted to evaluate the essentiality of dietary choline in such diets. The basal diet used in both experiments contained 32 g crude protein/100 g diet (10.1 g crude protein from casein and gelatin, and 21.9 g from a crystalline L-amino acid mixture). The total sulfur amino acid (TSAA) concentration of the basal diet was 0.28 g/100 g diet, Met:Cys 89:11. In Experiment 1, a 4x2 design was used in which crystalline L-methionine was added to the basal diet resulting in four levels of TSAA (0.28, 0.50, 0.75 or 1.0 g/100 g diet, Met:Cys 89:11, 94:6, 96:4, or 97:3, respectively). At each level of TSAA, diets also contained either 0 or 1 g choline/kg diet supplied as choline chloride. Weight gain, feed efficiency (FE) and serum methionine concentrations were significantly affected by dietary TSAA concentration, but not by dietary choline concentration or the interaction between TSAA and choline. Weight gain, feed efficiency and serum methionine concentrations indicated that the TSAA requirement was 0.5 g/100 g diet. In the second experiment, diets were formulated to contain either 0.28 or 0.5 g TSAA/100 g diet, Met:Cys 89:11 or 94:6, respectively, and graded levels of choline ranging from 1 to 4 g/kg diet in gradations of 1 g/kg. Dietary methionine significantly affected weight gain and FE, whereas dietary choline significantly affected weight gain, FE and survival, and the interaction of methionine and choline significantly affected weight gain. Fish fed diets containing 0.5 g TSAA/100 g diet and 3 g choline chloride/kg diet exhibited the highest weight gain, feed efficiency and survival. On the basis of these data, it seems clear that juvenile tilapia require choline in certain dietary formulations.

Enhanced anti-influenza activity of a surfactant protein D and serum conglutinin fusion protein

We previously demonstrated that bovine serum conglutinin has markedly greater ability to inhibit influenza A virus (IAV) infectivity than other collectins. We now show that recombinant conglutinin and a chimeric protein containing the NH(2) terminus and collagen domain of rat pulmonary surfactant protein D (rSP-D) fused to the neck region and carbohydrate recognition domain (CRD) of conglutinin (termed SP-D/Cong(neck+CRD)) have markedly greater ability to inhibit infectivity of IAV than wild-type recombinant rSP-D, confirming that the potent IAV-neutralizing activity of conglutinin resides in its neck region and CRD. Furthermore, by virtue of incorporation of the NH(2) terminus and collagen domain of SP-D, SP-D/Cong(neck+CRD) caused substantially greater aggregation of IAV particles and enhancement of neutrophil binding of, and H(2)O(2) responses to, IAV than recombinant conglutinin or recombinant rSP-D. Hence, SP-D/Cong(neck+CRD) combined favorable antiviral and opsonic properties of conglutinin and SP-D. This study demonstrates an association of specific structural domains of SP-D and conglutinin with specific functional properties and illustrates that antimicrobial activities of wild-type collectins can be enhanced through recombinant strategies.

Inhibition of denitrification by ultraviolet radiation

It has been shown that UV-A (lambda=320-400 nm) and UV-B (lambda=280-320 nm) inhibit photosynthesis, nitrogen fixation and nitrification. The purpose of this study was to determine the effects, if any, on denitrification in a microbial community inhabiting the intertidal. The community studied is the microbial mat consisting primarily of Lyngbya that inhabits the Pacific marine intertidal, Baja California, Mexico. Rates of denitrification were determined using the acetylene blockage technique. Pseudomonas fluorescens (ATCC #17400) was used as a control organism, and treated similarly to the mat samples. Samples were incubated either beneath a PAR transparent, UV opaque screen (OP3), or a mylar screen to block UV-B, or a UV transparent screen (UVT) for 2 to 3 hours. Sets of samples were also treated with nitrapyrin to inhibit nitrification, or DCMU to inhibit photosynthesis and treated similarly. Denitrification rates were greater in the UV protected samples than in the UV exposed samples the mat samples as well as for the Ps fluorescens cultures. Killed controls exhibited no activity. In the DCMU and nitrapyrin treated samples denitrification rates were the same as in the untreated samples. These data indicate that denitrification is directly inhibited by UV radiation.

Necropsy and histopathologic findings in 14 African hedgehogs (Atelerix albiventris): a retrospective study

From fiscal years 1992 through 1996, 14 African hedgehog (Atelerix albiventris) cases were submitted to the Animal Disease Diagnostic Laboratory at Purdue University. The most common diagnoses were splenic extramedullary hematopoiesis (91%), hepatic lipidosis (50%), renal disease (50%), and neoplastic disease (29%). Other less frequent necropsy findings were myocarditis (21%), colitis (14%), bacterial septicemia (14%), and pneumonia (14%). The data indicate that splenic extramedullary hematopoiesis, hepatic lipidosis, renal disease, and neoplasms are frequent postmortem findings in hedgehogs.

Influenza A virus up-regulates neutrophil adhesion molecules and adhesion to biological surfaces

Influenza A virus (IAV) binds to sialylated neutrophil surface components (e.g., CD43 and sialyl Lewisx antigen) and induces both activation and functional depression of neutrophils. We report that IAV enhanced neutrophil adhesion to surfaces coated with serum or serum components, but not to uncoated plastic. IAV up-regulated expression of integrins (CD11b and CD11c) and carcinoembryonic-related antigens on neutrophils, while reducing expression of CD43, L-selectin, and P-selectin glycoprotein ligand (PSGL). Although treatment of neutrophils with elastase or Osialoglycoprotease decreased surface CD43 and PSGL, they did not reduce binding of IAV to neutrophils, implying that IAV can bind to alternate binding sites in the absence of CD43. Pretreatment of neutrophils with elastase also did not prevent IAV from increasing expression of integrins and enhancing adhesion. Up-regulation of adhesion molecules and adhesion are important, previously unrecognized, features of neutrophil activation by IAV. Further studies will be needed to clarify the mechanism of these effects.

Influenza A virus accelerates neutrophil apoptosis and markedly potentiates apoptotic effects of bacteria

Neutrophils are recruited into the airway in the early phase of uncomplicated influenza A virus (IAV) infection and during the bacterial superinfections that are a significant cause of morbidity and mortality in IAV-infected subjects. In this report, we show that IAV accelerates neutrophil apoptosis. Unopsonized Escherichia coli had similar effects, although apoptotic effects of opsonized E coli were greater. When neutrophils were treated with both IAV and unopsonized E coli, a marked enhancement of the rate and extent of neutrophil apoptosis occurred as compared with that caused by either pathogen alone. Treatment of neutrophils with IAV markedly increased phagocytosis of E coli. Simultaneous treatment of neutrophils with IAV and E coli also elicited greater hydrogen peroxide production than did either pathogen alone. IAV increased neutrophil expression of Fas antigen and Fas ligand, and it also increased release of Fas ligand into the cell supernatant. These findings may have relevance to the understanding of inflammatory responses to IAV in vivo and of bacterial superinfection of IAV-infected subjects.

Edible mushroom (Agaricus bisporus) lectin, which reversibly inhibits epithelial cell proliferation, blocks nuclear localization sequence-dependent nuclear protein import

The Galbeta1-3GalNAcalpha (TF antigen)-binding lectin (ABL) from the common edible mushroom (Agaricus bisporus) has a potent anti-proliferative effect without any apparent cytotoxicity. This unusual combination of properties prompted investigation of its mechanism of action. In contrast to soluble lectin, agarose-immobilized, and hence noninternalizable ABL had no effect on proliferation of HT29 colon cancer cells. Electron microscopy of HT29 cells incubated with fluorescein- and gold-conjugated ABL showed internalization of the lectin into endocytotic vesicles and multivesicular bodies. Confocal microscopy showed perinuclear accumulation of fluorescein isothiocyanate-conjugated lectin, which also inhibits HT29 cell proliferation, raising the possibility that the lectin might interfere with nuclear pore function. Transport of heat shock protein 70 into the nucleus in response to heat shock was blocked by preincubation of HT29 cells for 6 h with 40 micrograms/ml ABL. In digitonin-permeabilized cells, nuclear uptake of bovine albumin conjugated to a nuclear localization sequence (NLS)-containing peptide was also inhibited by a 15-min preincubation with 40-100 micrograms/ml ABL. In contrast, serum-stimulated nuclear translocation of mitogen-activated protein kinase, which is NLS-independent, was not affected by pretreatment of cells with the lectin. These results suggest that the anti-proliferative effect of ABL is likely to be a consequence of the lectin trafficking to the nuclear periphery, where it blocks NLS-dependent protein uptake into the nucleus.

Controlling denitrification in closed artificial ecosystems

Denitrification, the dissimilatory reduction of NO3- to N2O and N2, is found in a wide variety of organisms. In closed artificial systems, especially closed plant growth chambers, a significant loss of fixed-N occurs through denitrification, thereby decreasing the efficiency of the system and fouling the atmosphere with N2O. Denitrification is a form of anaerobic respiration. Whenever available, however, denitrifiers preferentially use O2 as their terminal electron acceptor. As a result, rates of denitrification and growth are a function of O2. Typically, in closed systems O2 consumption is greater than the diffusion of O2 through the medium to the cell, decreasing the O2 level near the cell and denitrification occurs. Using Pseudomonas fluorescens (ATCC # 17400) as a model organism grown in a two L bioreactor under varying levels of O2 we studied its effects on population growth and its ability to mitigate denitrification in closed systems. The results indicate that denitrification occurs in a closed system even when it is considered aerobic, that is well mixed and sparged with either air, or sufficient pure O2 to cause a complete turnover in the gaseous atmosphere in the bioreactor vessel every five minutes.

Real-time imaging of gene expression in single living cells

Recent advances in reporter gene technologies are now allowing us to image gene transcription at the single cell level, using either fluorescence or luminescence microscopy. Here, the basis of these techniques is outlined and their advantages and disadvantages in various biological systems are discussed.

Pulmonary surfactant proteins A and D enhance neutrophil uptake of bacteria

The collectins are a class of collagenous lectin proteins present in serum and pulmonary secretions [pulmonary surfactant protein (SP) A and SP-D] that are believed to participate in innate immune responses to various pathogens. With the use of flow cytometric and fluorescent-microscopic assays, SP-A and SP-D were shown to increase calcium-dependent neutrophil uptake of Escherichia coli, Streptococcus pneumoniae, and Staphylococcus aureus. Evidence is provided that the collectins enhanced bacterial uptake through a mechanism that involved both bacterial aggregation and direct actions on neutrophils. The degree of multimerization of SP-D preparations was a critical determinant of both aggregating activity and potency in enhancing bacterial uptake. The mechanisms of opsonizing activity of SP-D and SP-A differed in important respects from those of opsonizing antibodies. These results provide the first evidence that surfactant collectins may promote neutrophil-mediated clearance of bacteria in the lung independently of opsonizing antibody.

Dynamic changes in prolactin promoter activation in individual living lactotrophic cells

The firefly luciferase gene has become widely used as a convenient reporter for studies of gene promoter regulation. Very recently, the development of ultralow-light imaging cameras has enabled the quantitative digital imaging of light signals resulting from luciferase activation in the presence of luciferin substrate. We have applied this technology to the study of PRL promoter activation in individual pituitary tumor cells to study the temporal and spatial characteristics of the expression of a well-characterized pituitary hormone gene. Rat pituitary GH3 cells were transfected by lipofection with a luciferase reporter gene linked to 5000 bp from the human PRL gene 5'-flanking region. A series of stably transfected cell clones were generated, and one of these was chosen for detailed study on the basis of appropriate regulation of high-level luciferase expression by a series of known stimuli including TRH, forskolin, the calcium channel agonist Bay K8644, and basic fibroblast growth factor (bFGF). These cells were subjected to direct imaging of luciferase activity using a Hamamatsu photon-counting camera linked to a Zeiss Axiovert microscope with an Argus-50 image processor. Cells were exposed to 1 mM luciferin, and images were integrated over 30-min periods for up to 72 h. The total photon count over a given field settled to steady levels within 10 h and then remained constant for over 55 h. Addition of forskolin, TRH, or bFGF increased the total photon count of fields of 20-100 cells by 2- to 4-fold consistent with previous data from transient expression assays using the human PRL promoter. Individual cells, on the other hand, showed marked marked temporal and spatial heterogeneity and variability of luciferase expression when studied at 3-h intervals. Unstimulated cells showed variable luciferase expression with up to 40-fold excursions in photon counts per single cell area within 12-h periods. Stimulation of cells with either TRH, forskolin, or bFGF resulted in smooth increases in photon output over fields of 20-100 cells, but again individual cell responses differed widely, with some cells showing slow progressive rises in photon output, others showing phasic or transient responses, and yet others showing no response. In conclusion, we found a surprising degree of heterogeneity and temporal variability in the level of gene expression in individual living pituitary tumor cells over long periods of time, with markedly divergent responses to hormonal or intracellular stimulation. The use of stably transfected clonal cell lines with extended periods of reporter gene imaging offers a valuable insight into control of gene expression in living cells in real time.

Hospitalization rates of tuberculosis in U.S. Navy enlisted personnel: a 15-year perspective

The epidemiology of tuberculosis in this country is changing because of a combination of biological and social factors. The recent use of DNA fingerprinting of Mycobacterium tuberculosis using restriction-fragment-length polymorphism analysis has suggested that nearly one-third of new cases of tuberculosis being reported in a large metropolitan city is a result of recent infection. The immunosuppression of individuals with the human immunodeficiency virus and the prevalence of multiple drug-resistant tuberculosis has resulted in a renewed interest in the epidemiology and prevention of this disease. To determine the magnitude of the problem in the U.S. Navy enlisted population, a computer search of more than one million inpatient hospitalization records from January 1980 to December 1994 was performed. Total first hospitalization rates for all cases of tuberculosis during this period ranged from 2.2 per 100,000 person-years at risk in white females to 27.5 per 100,000 person-years in males, race "other" (includes mostly Filipinos and Asian-Americans). First hospitalization rates across all cases of tuberculosis declined during this period from a high of 8.7 per 100,000 in 1980 to a low of 2.2 per 100,000 in 1994.