[Compartment syndrome caused by rhabdomyolysis in the context of pychogenic polydipsia]

Psychogenic polydipsia leading to severe hyponatremia is well documented in the literature. This electrolyte disorder can result in encephalopathy, cerebral edema and epileptic seizures. Another rare effect is rhabdomyolysis with all its well known complications (e.g. renal failure, hyperkalemia and cardiac arrhythmia) and even resulting in compartment syndrome due to severe muscle edema. We present the case of a patient with severe hyponatremia caused by psychogenic polydipsia leading to rhabdomyolysis and compartment syndrome.

Reflection coefficient and permeability of urea in the proximal convolution of the rat kidney : An application of non-equilibrium thermodynamics for a multicomponent system with active transport

The transport theory of Kedem and Katchalsky which was derived for passive transport in a two-compartment system is generalized for a multicomponent system with active transport, so that it can be applied to more complicated biological membranes.Equations have been derived to describe the transport of urea through the proximal convolution of the rat kidney and the permeability and the reflection coefficient have been determined. The permeability coefficient[Formula: see text] measured with the microperfusion and stop flow microperfusion methods, was found to be 6.0 and 5.2×10(-5) mm(2)/sec, respectively.The reflection coefficient (σ) was determined in a stationary state situation and found to be 0.68. Earlier free flow micropuncture results together with theP u andσ u of this study indicate that 50% of the filtered urea is reabsorbed proximally and that approximately half of this amount is reabsorbed by solvent drag and the rest by diffusion.In the Appendix, a theoretical treatment of nonelectrolyte transport in a multicomponent system with active transport is given.

Coherent transients in the femtosecond photoassociation of ultracold molecules

We demonstrate the photoassociation of ultracold rubidium dimers using coherent femtosecond pulses. Starting from a cloud of ultracold rubidium atoms, electronically excited rubidium molecules are formed with shaped photoassociation pump pulses. The excited state molecules are projected with a time-delayed probe pulse onto molecular ion states which are detected in a mass spectrometer. Coherent transient oscillations of the excited state population are observed in the wings of the pump pulse, in agreement with the time-dependent solution of the Schrödinger equation of the excitation process.

An integrated gene annotation and transcriptional profiling approach towards the full gene content of the Drosophila genome

A novel Drosophila microarray constructed on the basis of an integrated in silico/wet biology approach provides evidence for the transcription of approximately 2,600 additional genes. Validation indicates a lower limit of 2,000 novel annotations, thus raising the number of genes that make a fly.

Background

While the genome sequences for a variety of organisms are now available, the precise number of the genes encoded is still a matter of debate. For the human genome several stringent annotation approaches have resulted in the same number of potential genes, but a careful comparison revealed only limited overlap. This indicates that only the combination of different computational prediction methods and experimental evaluation of such in silico data will provide more complete genome annotations. In order to get a more complete gene content of the Drosophila melanogaster genome, we based our new D. melanogaster whole-transcriptome microarray, the Heidelberg FlyArray, on the combination of the Berkeley Drosophila Genome Project (BDGP) annotation and a novel ab initio gene prediction of lower stringency using the Fgenesh software.

Results

Here we provide evidence for the transcription of approximately 2,600 additional genes predicted by Fgenesh. Validation of the developmental profiling data by RT-PCR and in situ hybridization indicates a lower limit of 2,000 novel annotations, thus substantially raising the number of genes that make a fly.

Conclusions

The successful design and application of this novel Drosophila microarray on the basis of our integrated in silico/wet biology approach confirms our expectation that in silico approaches alone will always tend to be incomplete. The identification of at least 2,000 novel genes highlights the importance of gathering experimental evidence to discover all genes within a genome. Moreover, as such an approach is independent of homology criteria, it will allow the discovery of novel genes unrelated to known protein families or those that have not been strictly conserved between species.

[A head-mounted display system for augmented reality: initial evaluation for interventional MRI]

PURPOSE

To discuss the technical details of a head mounted display with an augmented reality (AR) system and to describe a first pre-clinical evaluation in interventional MRI.

METHOD

The AR system consists of a video-see-through head mounted display (HMD), mounted with a mini video camera for tracking and a stereo pair of mini cameras that capture live images of the scene. The live video view of the phantom/patient is augmented with graphical representations of anatomical structures from MRI image data and is displayed on the HMD. The application of the AR system with interventional MRI was tested using a MRI data set of the head and a head phantom.

RESULTS

The HMD enables the user to move around and observe the scene dynamically from various viewpoints. Within a short time the natural hand-eye coordination can easily be adapted to the slightly different view. The 3D perception is based on stereo and kinetic depth cues. A circular target with a diameter of 0.5 square centimeter was hit in 19 of 20 attempts. In a first evaluation the MRI image data augmented reality scene of a head phantom allowed good planning and precise simulation of a puncture.

CONCLUSION

The HMD in combination with AR provides a direct, intuitive guidance for interventional MR procedures.

[Effect of extracorporeal shockwave therapy on vascular regulation. Infrared thermography in epicondylitis humeri radialis]

BACKGROUND

Extracorporeal shockwave therapy (ESWT) is recommended as an alternative treatment for lateral epicondylitis (LE). An influence on the blood perfusion is considered to be one possible effect. Infrared thermography is used in this trial to measure effects of ESWT on the thermal regulation in the target area.

METHODS

33 patients with chronic LE were examined in a prospective, placebo-controlled single blind study with an independent observer. 3 x 2000 impulses of an energy flux density ED+ 0.22 mJ/mm2 were applied under local anaesthesia as verum-ESWT. Placebo-ESWT was performed under the same conditions. One elbow was treated, the other served as control. Before and after each shockwave application and after 12 weeks skin temperature was measured on both elbows at three predefined points by infrared thermography.

RESULTS

While a significant decrease in the skin temperature was found on the treated and sham-treated sides opposed to the contralateral side, there was no difference between the real shockwave treatment and placebo therapy. Responder and Non-responder to the treatment could not be distinguished during the therapy.

DISCUSSION

Infrared thermography was proved to be a valuable additional technical instrument for diagnosis of LE, but is not an appropriate instrument to predict the clinical outcome in patients treated with ESWT. A noted reduction of skin temperature on the treated side is not due to specific effects of the shockwaves. It is unlikely that ESWT as applied has an influence on thermal regulation in the target area. These findings are supported by negative results of experimental and clinical trials.

Towards an internet civil defence against bioterrorism

Approaches towards the public-health prevention of bioterrorism are too little, and too late. New information-based approaches could yield better homeland protection. An internet civil defence is presented where millions of eyes could help to identify suspected cases of bioterrorism, with the internet used to report, confirm, and prevent outbreaks.

TAFII250

Activation of RNA-polymerase-II-dependent transcription involves conversion of signals provided by gene-specific activator proteins into the synthesis of messenger RNA. This conversion requires dynamic structural changes in chromatin and assembly of general transcription factors (GTFs) and RNA polymerase II at core promoter sequence elements surrounding the transcription start site of genes. One hallmark of transcriptional activation is the interaction of DNA-bound activators with coactivators such as the TATA-box binding protein (TBP)-associated factors (TAFIIs) within the GTF TFIID. TAFII250 possesses a variety of activities that are likely to contribute to the initial steps of RNA polymerase II transcription. TAFII250 is a scaffold for assembly of other TAFIIs and TBP into TFIID, TAFII250 binds activators to recruit TFIID to particular promoters, TAFII250 regulates binding of TBP to DNA,TAFII250 binds core promoter initiator elements,TAFII250 binds acetylated lysine residues in core histones, and TAFII250 possesses protein kinase, ubiquitin-activating/conjugating and acetylase activities that modify histones and GTFs. We speculate that these activities achieve two goals - (1) they aid in positioning and stabilizing TFIID at particular promoters, and (2) they alter chromatin structure at the promoter to allow assembly of GTFs - and we propose a model for how TAFII250 converts activation signals into active transcription.

[European Agency for the Evaluation of Medicinal Products: five years experience]

The "European Agency for the Evaluation of Medicinal Products" (EMEA) is since 1995 primarily responsible for the scientific evaluation of applications for a European marketing authorisation for medicinal products derived from biotechnology and other high technology (centralised procedure). For other products, the EMEA arbitrates where mutual recognition of national marketing authorisations between the Member States is not possible (decentralised procedure). European patients are now able to have speedier access to new drugs, usually within one year. The new system also helps to reinforce the safety of medicines for humans and animals, particularly through a pharmacovigilance network and the establishment of safe limits for residues in food-producing animals.

Oxygenation during one-lung ventilation: the effects of inhaled nitric oxide and increasing levels of inspired fraction of oxygen

We studied whether inhaled nitric oxide (NO) would improve arterial oxygen tension (PaO(2)) and reduce the occurrence of oxygen saturation of hemoglobin (O(2)Hb) < 90% during one-lung ventilation (OLV). One-hundred-fifty-two patients were ventilated either with or without NO (20 ppm) with an inspired fraction of oxygen (FIO(2)) of either 0.3, 0.5, or 1.0 during OLV. Anesthesia was induced and maintained with propofol, remifentanil, and rocuronium IV, and lung separation was achieved with a double-lumen tube. During OLV, we set positive end-expiratory pressure at 5 cm H(2)O, peak pressure at 30 cm H(2)O, and end-tidal CO(2) at 30 mm Hg. The nonventilated lung was opened to room air and collapsed. During OLV, three consecutive measurements were performed every 10 min. The operated lung was temporarily ventilated if pulse oximetric saturation (SpO(2)) decreased to < 91%. SpO(2) <9 1% occurred in 2 of the 152 patients. SpO(2) overestimated O(2)Hb by 2.9% +/- 0.1%. NO failed to improve oxygenation or alter occurrence of O(2)Hb < 90% during OLV across all time points and all levels of FIO(2). Increasing FIO(2) increased oxygenation and decreased occurrence of O(2)Hb < 90% (P: < 0.001). At FIO(2) = 1, PaO(2) was higher (P < 0.01) and O(2)Hb < 90% rate tended to be lower (P = 0.1) during right versus left lung ventilation. PaO(2) was higher in patients undergoing pneumonectomy and lobectomy than in those undergoing metastasectomy or video-assisted operations (P < 0.05).

IMPLICATIONS

Inhaled nitric oxide failed to improve oxygenation during one-lung ventilation. Oxygenation during one-lung ventilation was improved with increasing levels of FIO(2) during ventilation of the right versus the left lung and with increasing pathology of the nonventilated lung.

Ubiquitin-activating/conjugating activity of TAFII250, a mediator of activation of gene expression in Drosophila

Ubiquitination of histones has been linked to the complex processes that regulate the activation of eukaryotic transcription. However, the cellular factors that interpose this histone modification during the processes of transcriptional activation are not well characterized. A biochemical approach identified the Drosophila coactivator TAFII250, the central subunit within the general transcription factor TFIID, as a histone-specific ubiquitin-activating/conjugating enzyme (ubac). TAFII250 mediates monoubiquitination of histone H1 in vitro. Point mutations within the putative ubac domain of TAFII250 abolished H1-specific ubiquitination in vitro. In the Drosophila embryo, inactivation of the TAFII250 ubac activity reduces the cellular level of monoubiquitinated histone H1 and the expression of genes targeted by the maternal activator Dorsal. Thus, coactivator-mediated ubiquitination of proteins within the transactivation pathway may contribute to the processes directing activation of eukaryotic transcription.

[Europe and medicines: role of the EMEA]

F. Sauer. Ann Pharm Fr 2000, 58: 278-285. The new European authorization system has made considerable progress since 1995. The European Agency for the Evaluation of Medicinal Products (EMEA) is primarily responsible for the scientific evaluation of applications for a European marketing authorization for medicinal products derived from biotechnology and other high technology (centralised procedure). For other products, the EMEA arbitrates where mutual recognition of national marketing authorizations between the Member States is not possible (decentralised procedure). The EMEA co-ordinates the scientific resources made available by the national competent authorities of the Member States, including a network of over 2 000 European experts. The Opinions of the scientific committees of the EMEA (Committee for Proprietary Medicinal Products, CPMP, and Committee for Veterinary Medicinal Products, CVMP) are enforced by the European Commission, which has so far authorized 69 medicinal products for human and veterinary use. The confidence of industry, health professionals and consumers in the system is clear. European patients are now able to have speedier access to new drugs, usually within one year. The new system also helps to reinforce the safety of medicines for humans and animals, particularly through a pharmacovigilance network and the establishment of safe limits for residues in food-producing animals.

Exact (spiral + circles) scan region-of-interest cone beam reconstruction via backprojection

We present a (spiral + circles) scan cone beam reconstruction algorithm in which image reconstruction proceeds via backprojection in the object space. In principle, the algorithm can reconstruct sectional region-of-interest (ROI) in a long object. The approach is a generalization of the cone beam backprojection technique developed by Kudo and Saito in two aspects: the resource-demanding normalization step in the Kudo and Saito's algorithm is eliminated through the technique of data combination that we published earlier, and the elimination of the restriction that the detector be big enough to capture the entire cone beam projection of the ROI. Restricting the projection data to the appropriate angular range required by data combination can be accomplished by a masking process. Because of the simplification resulting from the elimination of the normalization step, the most time-consuming operations of the algorithm can be approximated by the efficient step of line-by-line ramp filtering the cone beam image in the direction of the scan path, plus a correction image. The correction image, which can be computed exactly, is needed because data combination is not properly matched at the mask boundary when ramp filtering is involved. Empirical two-dimensional (2-D) point spread function (PSF) is developed to improve matching with the correction image which is computed with finite samplings. The use of transition region to further improve matching is introduced. The results of testing the algorithm on simulated phantoms are presented.

Exact radon rebinning algorithm for the long object problem in helical cone-beam CT

This paper addresses the long object problem in helical cone-beam computed tomography. We present the PHI-method, a new algorithm for the exact reconstruction of a region-of-interest (ROI) of a long object from axially truncated data extending only slightly beyond the ROI. The PHI-method is an extension of the Radon-method, published by Kudo, Noo, and Defrise in issue 43 of journal Physics in Medicine and Biology. The key novelty of the PHI-method is the introduction of a virtual object fpsi(x) for each value of the azimuthal angle psi in the image space, with each virtual object having the property of being equal to the true object f(x) in some ROI omegam. We show that, for each psi, one can calculate exact Radon data corresponding to the two-dimensional (2-D) parallel-beam projection of fpsi(x) onto the meridian plane of angle psi. Given an angular range of length pi of such parallel-beam projections, the ROI omegam can be exactly reconstructed because f(x) is identical to fpsi(x) in Omegam. Simulation results are given for both the Radon-method and the PHI-method indicating that 1) for the case of short objects, the Radon- and PHI-methods produce comparable image quality, 2) for the case of long objects, the PHI-method delivers the same image quality as in the short object case, while the Radon-method fails, and 3) the image quality produced by the PHI-method is similar for a large range of pitch values.

hairy stripe 7 element mediates activation and repression in response to different domains and levels of Krüppel in the Drosophila embryo

The Drosophila gap gene Krüppel (Kr) encodes a zinc finger-type transcription factor required for controlling the spatial expression of other segmentation genes during early blastoderm stage. Here we show that two independent and transferable repressor domains of Krüppel act to control expression of the pair-rule gene hairy, and that the minimal cis-acting element of hairy stripe7 (h7) mediates either Krüppel-dependent activation or repression in different regions of the blastoderm embryo. The C-terminal region of Krüppel which encompasses the predominant repressor domain is not essential for activation, but is required to fully suppress h7-mediated transcription in response to high levels of Krüppel activity. This domain contains an interaction motif for dCtBP, a homologue of the human co-repressor CtBP. dCtBP activity is, however, dispensable for Krüppel-mediated repression in the embryo since Krüppel-mediated repression functions in the absence of dCtBP. Possible modes of h7-mediated gene regulation in response to the different domains and levels of Krüppel are discussed.

Rotational versus nonrotational forceps: maternal and neonatal outcomes

OBJECTIVE

Our purpose was to evaluate maternal and neonatal morbidity associated with rotations performed with Leff forceps in comparison with nonrotational forceps deliveries.

STUDY DESIGN

A review of 267 rotational and nonrotational forceps deliveries from August 1996 through February 1998 was performed. Multiple maternal and neonatal outcome measures were compared and results were analyzed by chi(2) with the Fisher exact test and the Student t test.

RESULTS

One hundred sixty-three traditional low-forceps or outlet forceps deliveries were compared with 104 rotational forceps deliveries performed with Leff forceps. There were no significant differences between the 2 groups in maternal age, gestational age, gravidity, parity, total labor duration, birth weight, and Apgar scores. There were significantly lower rates of episiotomy, third- and fourth-degree lacerations, and sulcus lacerations in the rotation group, and the second stage of labor was also shorter. The neonatal intensive care unit admission rate was higher in the rotation group; however, none of the admissions were directly related to the mode of delivery.

CONCLUSION

Rotational deliveries performed with Leff forceps are associated with less maternal morbidity and shorter second stage of labor than are deliveries performed with traditional forceps. Leff forceps are a safe option for rotation of the persistent occipitoposterior fetal position.

Epidemiologic and public health initiatives in telecommunication

Epidemiologic knowledge must be available widely in order to insure public health for all worldwide. The objective of this paper is to account for what has been done in epidemiologic telecommunication during the previous four years at the University of Montreal, and to discuss the future of telecommunication for public-health enhancement. The first step taken has been to set up a mailing list in methodological epidemiology. The second step has been the launching of a virtual seminar in theoretical epidemiology. It is advocated that virtuality is mandatory to disseminate public health information, but that several crucial issues must be solved before the objective can be reached, among them the cultural, political and ethical issues of the endeavor. This paper includes a critical appraisal of the consequences for under-developed countries of the worldwide telecommunication expansion in the field of public health.

Mesoderm-determining transcription in Drosophila is alleviated by mutations in TAF(II)60 and TAF(II)110

In Drosophila, a coordinate interplay between the Rel transcription factor Dorsal and the basic Helix-Loop-Helix transcription factor Twist initiates mesoderm formation by activating the zygotic expression of mesoderm-determining genes. Here, we show that TBP-associated-factors (TAF(II)s) within the basal transcription factor TFIID mediate transcriptional activation by Dorsal and Twist. Dorsal interacts with TAF(II)110 and TAF(II)60, while Twist contacts TAF(II)110. The TAF(II):activator interactions mediate simple and synergistic transactivation by Dorsal and Twist in vitro. Mutations in TAF(II)60 or TAF(II)110 alleviate the transcription of Dorsal and Twist target genes. Gene dosage assays imply that an interplay of Dorsal and Twist with TAF(II)110 is critically required for the activation of mesoderm-determining gene expression in the Drosophila embryo. The results provide evidence that TAF(II)-subunits within the TFIID complex play an important role during the molecular events leading to initiation of mesoderm formation in Drosophila.

Drosophila head segmentation factor buttonhead interacts with the same TATA box-binding protein-associated factors and in vivo DNA targets as human Sp1 but executes a different biological program

The Drosophila gene buttonhead (btd) is required for the establishment of three embryonic head segments. It encodes a zinc-finger-type transcription factor expressed in the corresponding head segment anlagen in the blastoderm stage embryo. The DNA-binding properties of the btd protein (BTD) are indistinguishable from the human transcription factor Sp1. Furthermore, BTD and Sp1 are capable of activating transcription in transfected cultured cells through interaction with the same DNA target sites. Herein we show that BTD and Sp1 functionally interact with the same TATA box-binding protein-associated factors and support in vitro transcription activation through these contacts. Transgene expression of BTD results in the rescue of the head segments that fail to develop in btd mutant embryos, whereas Sp1 or Sp1 containing the zinc finger region of BTD rescues mandibular segment development. The results suggest that BTD contains functional domains other than an equivalent DNA-binding region and interaction sites of the TATA box-binding protein-associated factors, which are necessary to establish head segments that fail to develop in response to Sp1.

Exact cone beam CT with a spiral scan

A method is developed which makes it possible to scan and reconstruct an object with cone beam x-rays in a spiral scan path with area detectors much shorter than the length of the object. The method is mathematically exact. If only a region of interest of the object is to be imaged, a top circle scan at the top level of the region of interest and a bottom circle scan at the bottom level of the region of interest are added. The height of the detector is required to cover only the distance between adjacent turns in the spiral projected at the detector. To reconstruct the object, the Radon transform for each plane intersecting the object is computed from the totality of the cone beam data. This is achieved by suitably combining the cone beam data taken at different source positions on the scan path; the angular range of the cone beam data required at each source position can be determined easily with a mask which is the spiral scan path projected on the detector from the current source position. The spiral scan algorithm has been successfully validated with simulated cone beam data.

A randomized clinical trial comparing misoprostol with prostaglandin E2 gel for preinduction cervical ripening

OBJECTIVE

Our purpose was to perform a randomized trial comparing intravaginal misoprostol to intravaginal prostaglandin E2 gel for preinduction cervical ripening evaluating efficacy and side effects.

STUDY DESIGN

Seventy-five women seen for induction of labor were randomized to receive 100 micrograms of intravaginal misoprostol or 5 mg of pharmacy-prepared intravaginal prostaglandin E2 gel for cervical ripening before oxytocin induction. Six hours after placement of the study agent, patients were given oxytocin if they were not in labor. The primary outcome measure was induction-to-delivery time; secondary measures were change in Bishop score, delivery mode, and side effects. Results were analyzed by the Student t test and Fisher's exact test, with p < 0.05 considered significant.

RESULTS

There was no difference in the incidence of primiparity or the median initial Bishop score between the two study groups. The mean time to delivery and the need for oxytocin was significantly less for subjects receiving misoprostol. There was no difference in the incidence of uterine hyperstimulation syndrome or cesarean delivery between the groups.

CONCLUSIONS

This randomized clinical trial indicates that misoprostol is efficacious for preinduction cervical ripening. Misoprostol use resulted in a significantly shorter induction-to-delivery time compared with prostaglandin E2 gel use. The side effects associated with misoprostol may be dose related, and further studies to identify the optimum dosage and interval are needed.

Mechanisms of transcriptional activation: differences and similarities between yeast, Drosophila, and man

Activation of transcription requires an interplay between enhancer-binding factors and components of the general transcription machinery. New developments within the past few years suggest that novel cofactors are required for relaying specific activation signals to the RNA polymerase II transcription complex in order to achieve enhanced levels of mRNA synthesis. The role of these different cofactors in mediating activation and potential differences in their utilization by divergent organisms, however, raise new questions about the mechanisms of transcriptional regulation.

The need for a global health disaster network

When a disaster occurs, a major difficulty is knowing where to find accurate information, and how to help coordinate efforts to share accurate information in a quick and organized manner. The establishment of a global information network, that is in place before a disaster occurs, could link all the communication efforts for relief. We propose that a Global Health Unit for Disaster and Relief Coordination be set up as part of the Global Health Network, utilizing the Internet as its backbone. This Unit would establish the links for the disaster information mosaic.

TAF(II)s mediate activation of transcription in the Drosophila embryo

Mutations in the genes for two highly conserved TAFs, TAF(II)60 and TAF(II)110, reduce transcription of Bicoid-dependent target genes in vivo. By means of several distinct genetic test systems, specific activator-TAF interactions are shown to support both simple and synergistic enhancement of transcription in the embryo. These studies provide in vivo evidence that TAFs can serve as coactivators to receive gene-specific transcriptional activation signals. This genetic system also presents the opportunity to study the function of basal transcription components in regulating development of complex organisms.

Gene regulation in the Drosophila embryo

Pattern formation in Drosophila depends on hierarchical interactions between the maternal and zygotic gene activities which subdivide the embryo into increasingly smaller metameric units along the anterior posterior axis. Here we describe those genes that encode the transcription factors which control precisely the expression of subordinate transcription factors in time and space. This regulation operates through the protein-protein interactions between transcription factors bound to the cis-acting enhancers, which eventually determine the frequency of transcription initiation by polymerase II. Our data show that taking into account the multiple transcriptional activators and repressors that bind to a typical enhancer element, it is likely that the regulation of gene expression in a given cell is defined by their concentration-dependent interplay which directs target gene expression in a position-dependent fashion.

DNA template and activator-coactivator requirements for transcriptional synergism by Drosophila bicoid

The template and coactivator requirements for synergistic transcription directed by a single activator, Bicoid (BCD), bound to multiple sites have been determined. Mutagenesis studies in combination with protein binding experiments and reconstituted transcription reactions identified two independent activation domains of BCD that target different coactivator subunits (TAFII110 and TAFII60) of the basal transcription factor IID (TFIID). The presence of both coactivators is required for BCD to recruit the TATA binding protein (TBP)-TAF complex to the promoter and direct synergistic activation of transcription. Thus, contact between multiple activation domains of BCD and different targets within the TFIID complex can mediate transcriptional synergism.

Multiple TAFIIs directing synergistic activation of transcription

Coordinate activation of transcription by multiple enhancer binding factors is essential for the regulation of pattern formation during development of Drosophila melanogaster. Cell-free transcription reactions are described that recapitulate transcriptional synergism directed by the Drosophila developmental regulators Bicoid (BCD) and Hunchback (HB). Within the basal transcription factor complex TFIID, two specific targets, TAFII110 and TAFII60, served as coactivators to mediate transcriptional activation by these two enhancer binding proteins. A quadruple complex containing TATA binding protein (TBP), TAFII250, TAFII110, and TAFII60 mediated transcriptional synergism by BCD and HB, whereas triple TBP-TAFII complexes lacking one or the other target coactivator failed to support synergistic activation. Deoxyribonuclease I footprint protection experiments revealed that an integral step leading to transcriptional synergism involves the recruitment of TBP-TAFII complexes to the promoter by way of multivalent contacts between activators and selected TAFIIs. Thus, the concerted action of multiple regulators with different coactivators helps to establish the pattern and level of segmentation gene transcription during Drosophila development.

Heterodimeric Drosophila gap gene protein complexes acting as transcriptional repressors

The Drosophila gap gene Krüppel (Kr) encodes a transcriptional regulator. It acts both as an integral part of the Drosophila segmentation gene in the early blastoderm and in a variety of tissues and organs at later stages of embryogenesis. In transfected tissue culture cells, the Kr protein (Kr) was shown to both activate and repress gene expression in a concentration-dependent manner when acting from a single binding site close to the promoter. Here we show that KR can associate with the transcription factors encoded by the gap genes knirps (kni) and hunchback (hb) which affect KR-dependent gene expression in Drosophila tissue culture cells. The association of DNA-bound hb protein or free kni protein with distinct but different regions of KR results in the formation of DNA-bound transcriptional repressor complexes. Our results suggest that individual transcription factors can associate to form protein complexes which act as direct repressors of transcription. The interactions shown here add an unexpected level of complexity to the control of gene expression.

Control of transcription by Krüppel through interactions with TFIIB and TFIIE beta

The zinc-finger protein Krüppel (Kr) is an integral part of the Drosophila segmentation gene cascade and is essential in organogenesis during later embryonic development. In tissue culture, Kr regulates transcription. Monomeric Kr can act as a transcriptional activator, whereas Kr dimers formed at high concentrations cause repression. Here we show that Kr-dependent control of transcription involves functional interactions with components of the basal RNA polymerase II transcription machinery, which includes the initiation factors TFIIA, B, E, F, H and I (refs 10, 11) as well as the TATA-binding protein (TBP) and TBP-associated factors (TAFs) contained in the multisubunit TFIID (ref. 12). Our results indicate that when acting from a site close to a basal promoter, monomeric Kr interacts with TFIIB to activate transcription, whereas an interaction of the Kr dimer with TFIIE beta, a subunit of TFIIE, results in transcriptional repression.