Variability in neuronal activity in primate cortex during working memory tasks

Persistent elevated neuronal activity has been identified as the neuronal correlate of working memory. It is generally assumed in the literature and in computational and theoretical models of working memory that memory-cell activity is stable and replicable; however, this assumption may be an artifact of the averaging of data collected across trials, and needs experimental verification. In this study, we introduce a classification scheme to characterize the firing frequency trends of cells recorded from the cortex of monkeys during performance of working memory tasks. We examine the frequency statistics and variability of firing during baseline and memory periods. We also study the behavior of cells on individual trials and across trials, and explore the stability of cellular firing during the memory period. We find that cells from different firing-trend classes possess markedly different statistics. We also find that individual cells show substantial variability in their firing behavior across trials, and that firing frequency also varies markedly over the course of a single trial. Finally, the average frequency distribution is wider, the magnitude of the frequency increases from baseline to memory smaller, and the magnitude of frequency decreases larger than is generally assumed. These results may serve as a guide in the evaluation of current theories of the cortical mechanisms of working memory.

Patterned firing of parietal cells in a haptic working memory task

Abstract Cells in the somatosensory cortex of the monkey are known to exhibit sustained elevations of firing frequency during the short-term mnemonic retention of tactile information in a haptic delay task. In this study, we examine the possibility that those firing elevations are accompanied by changes in firing pattern. Patterns are identified by the application of a pattern-searching algorithm to the interspike intervals of spike trains. By sequential use of sets of pattern templates with a range of temporal resolutions, we find patterned activity in the majority of the cells investigated. In general, the degree of patterning significantly increases during active memory. Surrogate analysis suggests that the observed patterns may not be simple linear stochastic functions of instantaneous or average firing frequency. Therefore, during the active retention of a memorandum, the activity of a 'memory cell' may be characterized not only by changes in frequency but also by changes in pattern.

FMRI study relevant to the Mozart effect: brain areas involved in spatial-temporal reasoning

Behavioral studies, motivated by columnar cortical model predictions, have given evidence for music causally enhancing spatial-temporal reasoning. A wide range of behavioral experiments showed that listening to a Mozart Sonata (K.448) gave subsequent enhancements. An EEG coherence study gave evidence for a carryover from that Mozart Sonata listening condition to the subsequent spatial-temporal task in specific cortical regions. Here we present fMRI studies comparing cortical blood flow activation by the Mozart Sonata vs. other music. In addition to expected temporal cortex activation, we report dramatic statistically significant differences in activation by the Mozart Sonata (in comparison to Beethoven's Fur Elise and 1930s piano music) in dorsolateral pre-frontal cortex, occipital cortex and cerebellum, all expected to be important for spatial-temporal reasoning. It would be of great interest to explicitly test this expectation. We propose an fMRI study comparing (subject by subject) brain areas activated in music listening conditions and in spatial-temporal tasks.

Reliable short-term memory in the trion model: toward a cortical language and grammar

It has previously been shown that Hebb learning in a single column in the trion model of cortical organization occurs by selection. Motivated by von Neumann's solution for obtaining reliability and by models of circulating cortical activity, we introduce Hebb intercolumnar couplings to achieve dramatic enhancements in reliability in the firing of connected columns. In order for these enhancements to occur, specific temporal phase differences must exist between the same inherent spatial-temporal memory patterns in connected columns. We then generalize the criteria of large enhancements in the global firing of the entire connected columnar network to investigate the case when different inherent memory patterns are in the columns. The spatial rotations as well as the temporal phases now are crucial. Only certain combinations of inherent memory patterns meet these criteria with the symmetry properties playing a major role. The columnar order of these memory patterns not in the same symmetry family can be extremely important. This yields the first higher-level architecture of a cortical language and grammar within the trion model. The implications of this result with regard to an innate human language and grammar are discussed.

Generation of retroviral packaging and producer cell lines for large-scale vector production and clinical application: improved safety and high titer

For many applications, human clinical therapies using retroviral vectors still require many technological improvements in key areas of vector design and production. These improvements include higher unprocessed manufacturing titers, complement-resistant vectors, and minimized potential to generate replication-competent retrovirus (RCR). To address these issues, we have developed a panel of human packaging cell lines (PCLs) with reduced homology between retroviral vector and packaging components. These reduced-homology PCLs allowed for the use of a novel high multiplicity of transduction ("high m.o. t.") method to introduce multiple copies of provector within vector-producing cell lines (VPCLs), resulting in high-titer vector without the generation of RCR. In a distinct approach to increase vector yields, we integrated manufacturing parameters into screening strategies and clone selection for large-scale vector production. Collectively, these improvements have resulted in the development of diverse VPCLs with unprocessed titers exceeding 2 x 10(7) CFU/ml. Using this technology, human Factor VIII VPCLs yielding titers as high as 2 x 10(8) CFU/ml unprocessed supernatant were generated. These cell lines produce complement-resistant vector particles (N. J. DePolo et al., J. Virol. 73: 6708-6714, 1999) and provide the basis for an ongoing Factor VIII gene therapy clinical trial.

Cross-modal and cross-temporal association in neurons of frontal cortex

The prefrontal cortex is essential for the temporal integration of sensory information in behavioural and linguistic sequences. Such information is commonly encoded in more than one sense modality, notably sight and sound. Connections from sensory cortices to the prefrontal cortex support its integrative function. Here we present the first evidence that prefrontal cortex cells associate visual and auditory stimuli across time. We gave monkeys the task of remembering a tone of a certain pitch for 10 s and then choosing the colour associated with it. In this task, prefrontal cortex cells responded selectively to tones, and most of them also responded to colours according to the task rule. Thus, their reaction to a tone was correlated with their subsequent reaction to the associated colour. This correlation faltered in trials ending in behavioural error. We conclude that prefrontal cortex neurons are part of integrative networks that represent behaviourally meaningful cross-modal associations. The orderly and timely activation of neurons in such networks is crucial for the temporal transfer of information in the structuring of behaviour, reasoning and language.

Increasing epithelial junction permeability enhances gene transfer to airway epithelia In vivo

Gene transfer to airway epithelia is the most direct approach for treating the progressive lung disease associated with cystic fibrosis. However, the transduction efficiency is poor when viral vectors are applied to the mucosal surface. We reported previously that gene transfer via the apical surface of human airway epithelia in vitro was improved by formulating vectors with ethyleneglycol-bis-(2-aminoethyl ether)- N,N,N',N'-tetraacetic acid (EGTA) in a hypotonic buffer. First, we investigated the mechanism for this enhancement. When 100-nm fluorescent beads were applied to the apical surface in the presence of EGTA, paracellular deposition of the particles was noted. Transmission electron microscopy verified that the epithelial junction complex was disrupted under these conditions. The Ca(2+) chelators EGTA, 1,2-bis (2-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid (BAPTA), and ethylenediaminetetraacetic acid all caused a rapid, reversible drop in transepithelial resistance and facilitated gene transfer with retrovirus or adenovirus in vitro. When Ca(2+) chelators were applied to rabbit tracheal epithelia or human nasal epithelia in vivo, the transepithelial voltage decreased, and amiloride sensitivity was lost, suggesting that epithelial junctions opened. Importantly, this novel formulation enhanced both retroviral- and adenoviral-mediated gene transfer to rabbit tracheal epithelia in vivo. This technique may have applications for vector or drug delivery to airway epithelia and other polarized cells.

Music enhances spatial-temporal reasoning: towards a neurophysiological basis using EEG

Motivated by predictions from the structured trion model of the cortex, based on Mountcastle's columnar organizational principle, behavioral experiments have demonstrated a causal short-term enhancement of spatial-temporal reasoning in college students following listening to a Mozart Sonata (K.448) but not in control conditions. An EEG coherence study reported presence of right frontal and left temporoparietal activity induced by listening to the Mozart Sonata, which carried over into the spatial-temporal tasks in three of the seven subjects. In this paper, we present further predictions from the trion model and discuss how the new SYMMETRIC analysis method can be used in EEG recordings to help determine the neurophysiological basis of specific music enhancing spatial-temporal reasoning. We conclude with potential clinical applications of major significance.

Detecting symmetric patterns in EEG data: a new method of analysis

Theoretical models of higher cognitive function predict that cortical activity will exhibit families of spatial-temporal patterns of activity whose individual members are related to each other by specific symmetry transformations. In the trion model, it is suggested that these inherent symmetries play a vital role in how we think and reason. We have developed a method of analysis (SYMMETRIC analysis), which detects families of patterns in EEG data, and characterizes the symmetry relationships between members of those pattern families. Using this analysis, significant symmetry families have been found in EEG and single unit spike train data. If symmetry is a crucial aspect of brain function, it is possible that different pathologies are associated with specific types of symmetry relationships in brain activity that could be detected in EEG data by a SYMMETRIC analysis.

The resistance of retroviral vectors produced from human cells to serum inactivation in vivo and in vitro is primate species dependent

The ability to deliver genes as therapeutics requires an understanding of the vector pharmacokinetics similar to that required for conventional drugs. A first question is the half-life of the vector in the bloodstream. Retroviral vectors produced in certain human cell lines differ from vectors produced in nonhuman cell lines in being substantially resistant to inactivation in vitro by human serum complement (F. L. Cosset, Y. Takeuchi, J. L. Battini, R. A. Weiss, and M. K. Collins, J. Virol. 69:7430-7436, 1995). Thus, use of human packaging cell lines (PCL) may produce vectors with longer half-lives, resulting in more-efficacious in vivo gene therapy. However, survival of human PCL-produced vectors in vivo following systemic administration has not been explored. In this investigation, the half-lives of retroviral vectors packaged by either canine D17 or human HT1080 PCL were measured in the bloodstreams of macaques and chimpanzees. Human PCL-produced vectors exhibited significantly higher concentrations of circulating biologically active vector at the earliest time points measured (>1, 000-fold in chimpanzees), as well as substantially extended half-lives, compared to canine PCL-produced vectors. In addition, the circulation half-life of human PCL-produced vector was longer in chimpanzees than in macaques. This was consistent with in vitro findings which demonstrated that primate serum inactivation of vector produced from human PCL increased with increasing phylogenetic distance from humans. These results establish that in vivo retroviral vector half-life correlates with in vitro resistance to complement. Furthermore, these findings should influence the choice of animal models used to evaluate retroviral-vector-based therapies.

Keratinocyte growth factor induced epithelial proliferation facilitates retroviral-mediated gene transfer to distal lung epithelia in vivo

BACKGROUND

Cell proliferation, vector titer and accessibility of target cells represent hurdles for efficient gene transfer to lung epithelia in vivo using recombinant murine leukemia (MuLV)-based retroviruses. We tested the hypothesis that the pulmonary epithelium is susceptible to retroviral-mediated gene transfer when stimulated to proliferate by a mitogen, keratinocyte growth factor (KGF).

METHODS

Rats received keratinocyte growth factor (KGF, 2.5 micrograms/g x 4 doses, two consecutive days) intratracheally followed by high titer amphotropic retrovirus expressing beta-galactosidase. Gene transfer was assessed five days later.

RESULTS

KGF stimulated transient proliferation in the bronchiolar and alveolar epithelia (30-40% PCNA positive cells at peak) which decreased to background levels seven days after administration. Gene transfer to epithelia (X-Gal positive cells) occurred more frequently in KGF treated rats, but proliferation exceeded the level of gene transfer. X-gal positive cells were noted in the alveolar epithelium and occasionally in the bronchiolar epithelium. In order to understand the discrepancy between the number of proliferating and transduced cells, primary rat tracheal epithelium cultured at the air-liquid interface was infected from either the apical or basolateral side. Gene transfer was achieved only through basolateral application of vector, suggesting that epithelial polarity represents a barrier to MuLV-based lung gene transfer in vivo.

CONCLUSIONS

KGF transiently stimulates epithelial proliferation in vivo, facilitating MuLV-based gene transfer. Retroviral vectors may encounter multiple barriers which have evolved to defend the lung from infections.

Influence of cell polarity on retrovirus-mediated gene transfer to differentiated human airway epithelia

Gene transfer with recombinant murine leukemia viruses (MuLV) provides the potential to permanently correct inherited lung diseases, such as cystic fibrosis (CF). Several problems prevent the application of MuLV-based recombinant retroviruses to lung gene therapy: (i) the lack of cell proliferation in mature pulmonary epithelia, (ii) inefficient gene transfer with a vector applied to the apical surface, and (iii) low titers of many retroviral preparations. We found that keratinocyte growth factor (KGF) stimulated proliferation of differentiated human tracheal and bronchial epithelia. Approximately 50% of epithelia divided in response to KGF as assessed by bromodeoxyuridine histochemistry. In airway epithelia stimulated to divide with KGF, high-titer ampho- and xenotropic enveloped vectors preferentially infected cells from the basal side. However, treatment with hypotonic shock or EGTA transiently increased transepithelial permeability, enhancing gene transfer with the vector applied to the mucosal surfaces of KGF-stimulated epithelia. Up to 35% of cells expressed the transgene after gene transfer. By using this approach, cells throughout the epithelial sheet, including basal cells, were targeted. Moreover, the Cl- transport defect in differentiated CF airway epithelia was corrected. These findings suggest that barriers to apical infection with MuLV can be overcome.

High-frequency transitions in cortical spike trains related to short-term memory

Single-unit spike trains recorded from parietal cortex of monkeys performing a tactile short-term memory task show characteristic fluctuations (transitions) in their firing frequency that are related to memory. Spike trains recorded during the memory period, when the animal must retain information for the short term, show a higher rate of such transitions than spike trains recorded during intertrial baseline periods. In the present study, an analysis of multiple temporal resolutions over which these transitions are observed reveals that the memory-related transitions occur most prominently in the 25-50 Hz range. The results of this study suggest that, in the monkey, high frequency fluctuations of neuronal discharge in the parietal cortex are correlated with haptic short-term memory. The presence of such fluctuations are also consistent with theoretical models of short-term memory.

Effects of keratinocyte and hepatocyte growth factor in vivo: implications for retrovirus-mediated gene transfer to liver

We have previously shown that intravenous administration of keratinocyte growth factor (KGF) induces hepatocyte proliferation, allowing for efficient and noninvasive in vivo gene transfer with high-titer retroviral vectors in mice. The distinctive periportal distribution of transduced cells led us to investigate the ability of virus-sized particles to perfuse the liver adequately after growth factor treatment. We found that perfusion was adequate, and that transduction was limited to the periportal region because only those cells were stimulated to divide. Cells in this region also showed increased expression of Ram-1, the receptor for the murine Moloney leukemia virus (MoMLV) amphotropic envelope, after KGF treatment. In further studies we found that recombinant hepatocyte growth factor (HGF) induces a different population of hepatocytes to divide and upregulate Ram-1. The differential pattern of induction suggested that combining KGF and HGF would improve gene transfer efficiency further. Indeed, simultaneous delivery of both growth factors leads to an overall increase in the number of proliferating cells. Importantly, when coupled with MoMLV delivery, efficiency of gene transfer increased. These results confirm the utility of growth factors for noninvasive hepatic gene transfer in mice, and demonstrate how experiments to define the mechanism of transduction can be taken advantage of to develop improved gene transfer protocols.

Symmetric temporal patterns in cortical spike trains during performance of a short-term memory task

The trion model is a highly structured representation of cortical organization, which predicts families of symmetric spatial-temporal firing patterns inherent in cortical activity. The symmetries of these inherent firing patterns are used by the brain in short-term memory to perform higher level computations. In the present study, symmetric temporal patterns were searched for in spike trains recorded from cells in parietal cortex of a monkey performing a short-term memory task. A new method of analysis was used to map neuronal firing into sequences of integers representing relative levels of firing rate about the mean (i.e. -1, 0 and 1). The results of this analysis show families of patterns related by symmetry operations. These operations are: i. the interchanging of all the +1's and -1's in a given pattern sequence (C symmetry), ii. the inverting of the temporal sequence of the mapping (T symmetry), and iii. the combination of the two previous operations (CT symmetry). Patterns of a given family are found across cells, especially in the memory periods of the task; in most cases they reoccur within a given spike train. The pattern families predicted by the model and reported here should be further investigated in multiple microelectrode and EEG recordings.

Binary mapping of cortical spike trains in short-term memory

Microelectrode studies in monkeys performing short-term memory tasks show the sustained elevated discharge of cortical neurons during the retention of recalled sensory information. Cortical cells that are part of memory networks are assumed to receive numerous inputs of excitatory as well as inhibitory nature and local as well as remote. Thus it is reasonable to postulate that the temporal and spatial summation of diverse inputs on any cell in an activated network will result in temporally discrete groups of spikes in its firing. The activation of a network in active memory supposedly increases the magnitude and diversity of those inputs and thus increases the discontinuities and frequency fluctuations in the firing of cells in the network. In this study we use a new method of analysis that allows the quantification of firing discontinuities in a spike train. We apply it to parietal cells recorded from monkeys during the performance of a tactile short-term memory task. In our method, time is divided into bins of equal duration and the measure of discontinuities is the total count of the number of transitions between consecutive time bins with and without spikes. The results of the analysis show that in many of the cells studied, discontinuities (transitions between spiking and nonspiking) reflect memory-related activity obscured in the measures of raw spike frequency over a wide range of frequencies. These cells show more firing transitions in active short-term memory than in baseline (intertrial) conditions.

Auditory memory cells in dorsolateral prefrontal cortex

The activity of single neurons was recorded extracellularly from dorsolateral prefrontal cortex (DPC) of monkeys during the performance of a cross-modal audio-visual short-term memory task. Cells in DPC show sustained elevated firing levels (higher than spontaneous discharge) during the retention of the auditory stimulus. In some cells this elevated firing was significantly different depending on the particular auditory memorandum of each trial. These results support the notion that DPC participates in auditory short-term memory and the integration of auditory and visual information for prospective action.

Photosynthetic strategies in leaves and stems of Egeria densa

Photosynthetic mechanisms have been compared in leaves and, separately, in stems of Egeria densa Planch. In order to correlate the structural and functional characteristics of the two organs (1) the ultrastructural features of leaves and stems have been studied and (2) their photosynthetic activity has been evaluated by measuring in vivo both oxygen evolution and the kinetics of chlorophyll fluorescence. The results confirm the aquatic behaviour of the leaf which is able to utilize inorganic C supplied both as CO2 and HCO 3 (-) . In this respect, the different wall organization found in the two cell layers of the leaf is particularly interesting, since it could be related to the known polar mechanism of inorganic-C uptake. The stem, by contrast, behaves rather as an aerial organ, needing very high CO2 concentrations in the aquatic environment in order to carry out photosynthesis. In the stem, the aerenchyma plays a role in supplying the green cells with gaseous respiratory CO2, thus facilitating the photosynthetic activity of the submerged stems.

Antiemetic efficacy of ondansetron after outpatient laparoscopy

The safety and efficacy of ondansetron were evaluated for the treatment of postoperative nausea and vomiting after laparoscopic surgical procedures. Seventy-one healthy, consenting outpatients were randomly assigned to one of two treatment groups according to a double-blind, placebo-controlled protocol. A standardized anesthetic technique consisting of alfentanil-thiopental-succinylcholine for induction and alfentanil-nitrous oxide-succinylcholine for maintenance of anesthesia was used. Patients in whom postoperative nausea and/or vomiting developed and persisted for greater than or equal to 10 min received equivolemic intravenous injections of either ondansetron (8 mg) or saline (placebo) over a 2-5 min period. Ondansetron significantly decreased the posttreatment nausea scores (vs placebo) without increasing sedation or producing changes in cardiorespiratory parameters. In the placebo-treated group, 92% of the patients experienced subsequent episodes of vomiting in the postanesthesia care unit compared with 51% of the patients in the ondansetron group. Finally, only 43% of the ondansetron-treated patients required a "rescue" antiemetic compared with 86% in the placebo group. Thus, ondansetron (8 mg IV) was associated with a decreased incidence of nausea and vomiting after outpatient laparoscopic procedures.

Purification of growth hormone-specific transcription factor GHF-1 containing homeobox

Pituitary-specific expression of the growth hormone (GH) gene is governed by a transcription factor, GHF-1, that binds to two sites within its promoter. Recently, GHF-1 was shown to be a member of the homeobox family of DNA-binding proteins. An important question is whether GHF-1 controls the expression of other pituitary specific genes, such as prolactin (Prl), expressed in closely related cell types. To this end, GHF-1 was purified from extracts of GH- and Prl-expressing pituitary tumor cells and identified as a 33-kilodalton polypeptide. Although GHF-1 bound to and activated the GH promoter, it did not recognize the Prl promoter. However, at least one other factor in the same extracts, which was easily separated from GHF-1, bound to several sites within the Prl but not the GH promoter. Antibodies to GHF-1 did not react with the Prl binding activity. These results imply that the pituitary-specific expression of GH and Prl is governed by two distinct trans-acting factors.

The pituitary-specific transcription factor GHF-1 is a homeobox-containing protein

Growth hormone factor 1 (GHF-1) is a pituitary-specific transcription factor that plays a critical role in cell type-specific expression of the growth hormone (GH) gene. Here, we describe the isolation of bovine and rat GHF-1 cDNA clones. These cDNAs encode proteins whose molecular mass, 33K, is identical to purified GHF-1 and whose sequence agrees with a partial GHF-1 peptide sequence. The predicted GHF-1 sequence contains a region, near its C-terminus, that exhibits considerable similarity to a homeobox consensus sequence. DNAase I footprinting with bacterially expressed fusion protein containing a fragment of GHF-1 encompassing the homeobox indicates that this region of the protein functions as its DNA binding domain. Expression of GHF-1 is restricted to cells of the somatotropic lineage in the pituitary. This remarkable specificity of GHF-1 expression correlates with the selective transcription of its target, the GH gene. Other mammalian homeobox-containing proteins may function similarly as transcription factors controlling cell type-specific expression in other locations.

A pituitary-specific trans-acting factor can stimulate transcription from the growth hormone promoter in extracts of nonexpressing cells

The growth hormone (GH) gene is specifically expressed in the anterior pituitary. The first 289 bp of the human (h)GH 5' region contains a promoter that is active only in pituitary-derived cell lines. These cell lines also contain a specific factor, GHF-1, that binds to two sites upstream to the hGH TATA box. Using in vitro transcription systems we demonstrate greater hGH promoter activity in extracts of GH-expressing GC cells than in extracts of nonexpressing HeLa cells. The two GHF-1 binding sites are essential promoter elements in GC extracts. Addition of GHF-1-containing fractions to HeLa extracts stimulates hGH promoter activity. Thus, GHF-1 appears to be a positively acting, cell-type- and promoter-specific transcription factor. Furthermore, the tissue specificity of the hGH promoter appears to be positively controlled by the abundance or activity of GHF-1.

Effect of supercooling and freezing on photosynthesis in freezing tolerant leaves of Afroalpine 'giant rosette' plants

The effect of supercooling and freezing on the photosynthetic capability of representatives of the permanent frost hardy giant rosette plants Dendrosenecio keniodendron, D. brassica and Lobelia telekii, of the tropical alpine regions was investigated with the non-invasive chlorophyll a fluorescence technique. While supercooling, normal chlorophyll a fluorescence kinetics exhibiting the sequence 0, I, (D), P, S, M, were recorded, however with some retardation of both, the fast and the slow characteristics as compared to those obtained at day-time temperature. As long as the leaves remained unfrozen, the rise of the variable fluorescence F _ν from the level 0 to P was inversely related to a drop of the temperature from about 0°C to-8°C. The increase of F _ν with lower temperature is understood to result from a decrease of the velocity of the quenching reactions while photoreduction of the primary electron acceptor appeared to be unimpeded. The second fluorescence maximum (M), usually interpreted to indicate the commencement of the biochemical reactions of photosynthesis was consistenly to be observed during supercooling. Fluoescence induction kinetics of frozen leaves showed only fast rise to presumably F _max which was not followed by a significant decay for as long as 4 min. The lack of substantial quenching indicates that in the freeze-dehydrated state neither reoxidation of the primary acceptor nor energetization of the thylakoid membrane was accomplished. This effect however was immediately and fully reserved upon thawing of the leaves when the usual fluorescence induction kinetics as well as normal rates of CO₂-uptake were observed. Thus the permanent frost-hardy afroalpine plants do not exhibit any even short-term memory effect of the nocturnal frost on such a delicate process as is photosynthesis.

Tissue-specific expression of the human growth hormone gene is conferred in part by the binding of a specific trans-acting factor

The molecular basis for the pituitary-specific expression of the human growth hormone (hGH) gene was investigated, by gene transfer and protein footprinting experiments. Plasmid constructs in which CAT or Neo transcription units are fused to a 0.5 kb fragment of the hGH 5' sequences were efficiently expressed in GC and GH3 cells, derived from a pituitary tumor, but not in cell lines of other origins, indicating the presence of a tissue-specific promoter. DNaseI footprinting experiments have identified at least three factors that specifically bind to the hGH 5' region. While two of these factors were also detected in extracts of non-expressing cells, the third factor, GHF-1, was detected only in extracts of GH expressing pituitary tumor cells. Mutagenesis experiments suggest that binding of GHF-1 and some of the other more ubiquitous factors is required for optimal hGH promoter activity in vivo. Tissue specificity of the hGH promoter therefore seems to be determined by the binding of at least one tissue-specific trans-acting factor, acting in concert with several other more ubiquitous, yet specific, DNA binding proteins.

Curved DNA: design, synthesis, and circularization

Curved DNA molecules and unusually small circles have been obtained by ligation of synthetic 21-base precursors: (sequence in text). The ligation resulted in the formation of double-stranded oligo-(precursor)s possessing a strong 10.5-base-pair (bp) periodicity of the runs of adenines. Two-dimensional polyacrylamide gel electrophoresis of the ligation products showed two distinct families of spots: (i) noncircular oligo(precursor)s of 21 to 231 bp (1- to 11-mers) and (ii) four circles from 105 to 168 bp (eluted and analyzed by denaturing gel electrophoresis). The noncircular oligomers exhibited anomalously slow migration, as if they were as much as three times longer than they actually are. The amount of circular products peaked sharply at approximately equal to 126 bp, near which size the circles have been estimated to be nonconstrained both torsionally and in terms of bending. The nonconstrained circularization provides a technique for the direct measurement of the inherent curvature of DNA in solution. From the size of the circles, an estimate of 8.7 degrees is obtained for the absolute value of the AA X TT wedge angle (roll and tilt combined).

Structure and expression of the vasoactive intestinal peptide (VIP) gene in a human tumor

To identify the VIP biosynthetic pathways, we have isolated the human VIP gene, using synthetic oligodeoxynucleotides. These specific hybridization probes were constructed according to the neuroblastoma VIP-cDNA sequence and contained up to 39 bases. The gene structure was deduced by direct chemical nucleotide sequencing. Six exons were thus far discovered; among them two short exons, one encoding VIP and the second encoding PHM-27 (a peptide having a N-terminal histidine and C-terminal methionine amide, closely related in sequence and activity to VIP). As a model system for VIP gene expression, we used a human buccal tumor producing elevated amounts of VIP. In these cells, a major transcript of the VIP-gene was identified as a long RNA containing intron sequences. The occurrence of elevated quantities of a high molecular weight, intron containing, gene transcript which is not processed directly into mature RNA suggests that VIP gene expression may be regulated at the RNA processing level.

Studies toward the biosynthesis of vasoactive intestinal peptide (VIP)

In view of the potential biological importance of VIP, we have begun to examine the regulation of its biosynthesis. For this purpose we have, as a first step, searched for an enriched source of VIP biosynthesis. By a combination of chromatographic procedures and radioimmunoassays we discovered an as yet unknown source for VIP production, namely a human buccal tumor, containing 0.67 +/- 0.05 ng VIP/micrograms protein which is greater than the richest source in brain (the cerebral cortex). Thus, we decided to use the tumor tissue for VIP-mRNA purification and characterization. To identify VIP-mRNA we are using as hybridization probes, synthetic oligodeoxynucleotides with relatively unambiguous nucleotide sequence complementary to the predicted VIP-mRNA sequence. These probes are synthesized, using the deoxynucleoside phosphoramidite approach, to a length of 17 bases each, and contain all the possible DNA sequences according to the genetic code. These specific probes are then radioactively labelled using the reaction catalyzed by the enzyme polynucleotide kinase and afterwards hybridized to mRNA, which had been resolved on denaturing agarose gels. Employing this approach, we identified a single putative VIP-mRNA band which was then partially purified by sucrose gradient centrifugation. Upon in vitro translation in a rabbit reticulocyte lysate cell free system, this mRNA was found to code for VIP immunoreactive proteins. In conclusion, our studies suggest the existence of high molecular weight precursors to VIP cross-reactive with anti-VIP antibodies, that are coded for by a partially purified mRNA containing VIP sequences.

Detection of mRNAs containing regulatory peptide coding sequences using synthetic oligodeoxynucleotides

To understand the regulation of the production of peptide hormones, it is vital to elucidate their biosynthetic pathways. We chose to study a major regulatory peptide, vasoactive intestinal peptide (VIP), a peptide possessing both neurotransmitter and neurohormone actions. To identify the specific peptide mRNA we are using, as hybridization probes, radiolabeled synthetic oligodeoxynucleotides with sequence complementary to the predicted peptide mRNA sequence. Employing this approach, we identified and partially purified a approximately 1600-base long mRNA containing VIP related sequences which can be translated in vitro into VIP-immunoreactive polypeptides. Such mRNA was detected in normal VIP producing tissue (rat brain), as well as in a tumor producing VIP (human buccal tumor). This mRNA differs in size from a known VIP-mRNA identified in human neuro-blastoma cells, suggesting the possibility of different VIP-mRNAs in different cell types.