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Biofilm production is an important step in the pathogenesis of S. epidermidis polymer-associated infections and depends on the expression of the icaADBC operon leading to the synthesis of a polysaccharide intercellular adhesin (PIA). The PIA represents a sugar polymer consisting of ß-1,6 linked N-acetyl glucosaminoglycans and mediates the intercellular adherence of the bacteria to each other and the accumulation of a multilayered biofilm. Epidemiological and experimental studies strongly suggest that PIA-production and subsequently biofilm formation contributes significantly to the virulence of specific S. epidermidis strains. This work aimed on the investigation of external factors regulating the ica expression in S. epidermidis. For this purpose, a reporter gene fusion between the ica promoter and the beta-galactosidase gene lacZ from E. coli was constructed and integrated into the chromosome of an ica positive S. epidermidis clinical isolate. The reporter gene fusion was used to investigate the influence of external factors and of sub-MICs of different antibiotics on the ica expression. It was shown that the S. epidermidis biofilm formation is growth phase dependent with a maximum expression in the late logarithmic and early stationary growth phase. The optimal expression was recorded at 42 °C at a neutral pH ranging from 7.0 to 7.5. The glucose content of the medium was found to be essential for biofilm formation, since concentrations of 1.5 to 2 per cent glucose induced the ica expression. In addition, external stress factors as high osmolarity (mediated by 3 to 5 per cent sodium chloride), and sub-lethal concentrations of detergents, ethanol, hydrogene peroxide, and urea significantly enhanced the biofilm production. Subinhibitory concentrations of tetracyline, the semisynthetic streptogramin quinupristin/dalfopristin and the streptogramin growth promoter virginiamycin were found to enhance the ica expression 8 to 11-fold, respectively, whereas penicillin, oxacillin, gentamicin, clindamycin, vancomycin, teicoplanin, ofloxacin, and chloramphenicol had no effects. A weak induction was recorded for sub-MICs of erythromycin. Both quinupristin/ dalfopristin and tetracyline exhibited a strong postexposure effect on the S. epidermidis ica expression, respectively, even when the substances were immediately removed from the growth medium. The results were confirmed by Northern blot analysis of the ica transcription and quantitative analysis of biofilm formation in a colorimetric assay. Expression of the icaprom::lacZ reporter gene plasmid in Bacillus subtilis and S. epidermidis revealed that the ica induction by sub-MICs of streptogramins and tetracycline might depend on unidentified regulatory elements which are specific for the staphylococcal cell. In contrast, the activation by external stress signals seems to be mediated by factors which are present both in Staphylococci and in Bacillus subtilis. Construction and analysis of an agr-mutant in a biofilm-forming S. epidermidis strain excluded the possibility that the Agr-quorum-sensing system significantly contributes to the ica expression in the stationary growth phase. However, clear evidence was provided that in S. aureus the ica transcription depends on the expression of the alternative transcription factor sigmaB, which represents a global regulator of the stress response in S. aureus as well as in B. subtilis. For this purpose, a sigB knockout mutant had been constructed in a biofilm-forming S. aureus. This mutant showed a markedly decrease of the ica transcription and biofilm-production, whereas a complement strain carrying the sigB gene on an expression vector completely restored the biofilm-forming phenotype of the S. aureus wild type. Southern blot analysis indicated that the the sigB gene is also present in S. epidermidis and Northern analyses of the sigB and the ica transcription revealed that both genes are activated under identical conditions (i. e. in the stationary growth phase and by external stress factors) suggesting a similar regulatory pathway as in S. aureus. However, since neither in S. aureus nor in S. epidermidis the ica promoter has obvious similiarities to known SigB-dependent promotoer sequences it is tempting to speculate that the ica activation is not directely mediated by SigB, but might be indirectely controlled by other SigB-dependent regulatory elements which remain to be elucidated.
The transmission of proliferative and developmental signals from activated cell-surface receptors to initiation of cellular responses in the nucleus is synergically controlled by the coordinated action of a diverse set of intracellular signalling proteins. The Ras/Raf/MEK/MAPK signalling pathway has been shown to control the expression of genes which are crucial for the physiological regulation of cell proliferation, differentiation and apoptosis. Within this signalling cascade, the Raf protein family of serine/threonine kinases serves as a central intermediate which connects to many of other signal transduction pathways. To elucidate the signalling functions of the different Raf kinases in motoneurons during development, the expression, distribution and subcellular localization of Rafs in the spinal cord and the facial nucleus in brainstem of mice at various embryonic and postnatal stages were investigated. Moreover, we have investigated the intracellular redistribution of Raf molecules in isolated motoneurons from 13 or 14 day old mouse embryos, after addition or withdrawal of neurotrophic factors to induce Raf kinases activation in vitro. Furthermore, in order to investigate the potential anti-apoptotic function of Raf kinases on motoneurons, we isolated motoneurons from B-raf-/- and c-raf-1-/- mouse embryos and analysed the survival and differentiation effects of neurotrophic factors in motoneurons lacking B-Raf and c-Raf-1. We provide evidence here that all three Raf kinases are expressed in mouse spinal motoneurons. Their expression increases during the period of naturally occurring cell death of motoneurons. In sections of embryonic and postnatal spinal cord, motoneurons express exclusively B-Raf and c-Raf-1, but not A-Raf, and subcellularly Raf kinases are obviously colocalized with mitochondria. In isolated motoneurons, most of the B-Raf or c-Raf-1 immunoreactivity is located in the perinuclear space but also in the nucleus, especially after activation by addition of CNTF and BDNF in vitro. We found that c-Raf-1 translocation from the cytosol into the nucleus of motoneurons after its activation by neurotrophic factors is a distinct event. As a central finding of our study, we observed that the viability of isolated motoneurons from B-raf but not c-raf-1 knockout mice is lost even in the presence of CNTF and other neurotrophic factors. This indicates that B-Raf but not c-Raf-1, which is still present in B-raf deficient motoneurons, plays a crucial role in mediating the survival effect of neurotrophic factors during development. In order to prove that B-Raf is an essential player in this scenario, we have re-expressed B-Raf in mutant sensory and motor neurons by transfection. The motoneurons and the sensory neurons from B-raf knockout mouse which were transfected with exogenous B-raf gene revealed the same viability in the presence of neurotrophic factors as primary neurons from wild-type mice. Our results suggest that Raf kinases have important signalling functions in motoneurons in mouse CNS. In vitro, activation causes redistribution of Raf protein kinases, particularly for c-Raf-1, from motoneuronal cytoplasm into the nucleus. This redistribution of c-Raf-1, however, is not necessary for the survival effect of neurotrophic factors, given that B-raf-/- motor and sensory neurons can not survive despite the presence of c-Raf-1. We hypothesize that c-Raf-1 nuclear translocation may play a direct role in transcriptional regulation as a consequence of neurotrophic factor induced phosphorylation and activation of c-Raf-1 in motoneurons. Moreover, the identification of target genes for nuclear translocated c-Raf-1 and of specific cellular functions initiated by this mechanism awaits its characterization.
The Mouthparts of Ants
(2001)
Ant mandible movements cover a wide range of forces, velocities and precision. The key to the versatility of mandible functions is the mandible closer muscle. In ants, this muscle is generally composed of distinct muscle fiber types that differ in morphology and contractile properties. Volume proportions of the fiber types are species-specific and correlate with feeding habits. Two biomechanical models explain how the attachment angles are optimized with respect to force and velocity output and how filament-attached fibers help to generate the largest force output from the available head capsule volume. In general, the entire mandible closer muscle is controlled by 10-12 motor neurons, some of which exclusively supply specific muscle fiber groups. Simultaneous recordings of muscle activity and mandible movement reveal that fast movements require rapid contractions of fast muscle fibers. Slow and accurate movements result from the activation of slow muscle fibers. Forceful movements are generated by simultaneous co-activation of all muscle fiber types. For fine control, distinct fiber bundles can be activated independently of each other. Retrograde tracing shows that most dendritic arborizations of the different sets of motor neurons share the same neuropil in the suboesophageal ganglion. In addition, some motor neurons invade specific parts of the neuropil. The labiomaxillary complex of ants is essential for food intake. I investigated the anatomical design of the labiomaxillary complex in various ant species focusing on movement mechanisms. The protraction of the glossa is a non muscular movement. Upon relaxation of the glossa retractor muscles, the glossa protracts elastically. I compared the design of the labiomaxillary complex of ants with that of the honey bee, and suggest an elastic mechanism for glossa protraction in honey bees as well. Ants employ two different techniques for liquid food intake, in which the glossa works either as a passive duct (sucking), or as an up- and downwards moving shovel (licking). For collecting fluids at ad libitum food sources, workers of a given species always use only one of both techniques. The species-specific feeding technique depends on the existence of a well developed crop and on the resulting mode of transporting the fluid food. In order to evaluate the performance of collecting liquids during foraging, I measured fluid intake rates of four ant species adapted to different ecological niches. Fluid intake rate depends on sugar concentration and the associated fluid viscosity, on the species-specific feeding technique, and on the extent of specialization on collecting liquid food. Furthermore, I compared the four ant species in terms of glossa surface characteristics and relative volumes of the muscles that control licking and sucking. Both probably reflect adaptations to the species-specific ecological niche and determine the physiological performance of liquid feeding. Despite species-specific differences, single components of the whole system are closely adjusted to each other according to a general rule.
Tropical rain forests and coral reefs are usually regarded as the epitome of complexity and diversity. The mechanisms, however, that allow so many species to coexist continuously, still need to be unraveled. Earlier equilibrium models explain community organization with a strict niche separation and specialization of the single species, achieved mainly by interspecific competition and consecutive resource partitioning. Recent non-equilibrium or stochastic models see stochastic factors ("intermediate disturbances") as more important. Such systems are characterized by broad niche overlaps and an unpredictable species composition. Mechanisms of coexistence are most interesting where species interactions are strongest and species packing is highest. This is the case within a functional group or guild where species use similar resources. In this project a community of seven closely related leaf beetle species (Chrysomelidae: Cassidinae) was investigated which coexist on a common host plant system (fam. Convovulaceae) in a tropical moist savanna (Ivory Coast, Comoé-Nationalpark). A broad overlap in the seasonal phenology of the leaf beetle species stood in contrast to a distinct spatial niche differentiation. The beetle community could be separated in a savanna-group (host plant: Ipomoea) and in a river side group (host plant: Merremia). According to a correspondence analysis the five species at the river side, using a common host plant, Merremia hederacea, proved to be predictable in their species composition. They showed a small scale niche differentiation along the light gradient (microhabitats). Laboratory studies confirmed differences in the tolerance towards high temperatures (up to 50°C in the field). Physiological trade-offs between phenology, microclimate and food quality seem best to describe patterns of resource use of the beetle species. Further a phylogeny based on mt-DNA sequencing of the beetle community was compared to its ecological resource use and the evolution of host plant use was reconstructed
Listeriae are Gram positive, facultative, saprophytic bacteria capable of causing opportunistic infections in humans and animals. This thesis presents three separate lines of inquiries that can lead to the eventual convergence of a global view of Listeria as pathogen in the light of evolution, genomics, and function. First, we undertook to resolve the phylogeny of the genus Listeria with the goal of ascertaining insights into the evolution of pathogenic capability of its members. The phylogeny of Listeriae had not yet been clearly resolved due to a scarcity of phylogenetically informative characters within the 16S and 23S rRNA molecules. The genus Listeria contains six species: L. monocytogenes, L. ivanovii, L. innocua, L. seeligeri, L. welshimeri, and L. grayi; of these, L. monocytogenes and L. ivanovii are pathogenic. Pathogenicity is enabled by a 10-15Kb virulence gene cluster found in L. seeligeri, L. monocytogenes and L. ivanovii. The genetic contents of the virulence gene cluster loci, as well as some virulence-associated internalin loci were compared among the six species. Phylogenetic analysis based on a data set of nucleic acid sequences from prs, ldh, vclA, vclB, iap, 16S and 23S rRNA genes identified L. grayi as the ancestral branch of the genus. This is consistent with previous 16S and 23S rRNA findings. The remainder 5 species formed two groupings. One lineage represents L. monocytogenes and L. innocua, while the other contains L. welshimeri, L. ivanovii and L. seeligeri, with L. welshimeri forming the deepest branch within this group. Deletion breakpoints of the virulence gene cluster within L. innocua and L. welshimeri support the proposed tree. This implies that the virulence gene cluster was present in the common ancestor of L. monocytogenes, L. innocua, L. ivanovii, L. seeligeri and L. welshimeri; and that pathogenic capability has been lost in two separate events represented by L. innocua and L. welshimeri. Second, we attempted to reconstitute L. innocua of its deleted virulence gene cluster, in its original chromosomal location, from the L. monocytogenes 12 Kb virulence gene cluster. This turned out particularly difficult because of the limits of genetic tools presently available for the organism. The reconstitution was partially successful. The methods and approaches are presented, and all the components necessary to complete the constructs are at hand for both L. innocua and the parallel, positive control of L. monocytogenes mutant deleted of its virulence gene cluster. Third, the sequencing of the entire genome of L. monocytogenes EGDe was undertaken as part of an EU Consortium. Our lab was responsible for 10 per cent of the labor intensive gap-closure and annotation efforts, which I helped coordinate. General information and comparisons with sister species L. innocua and a close Gram positive relative Bacillus subtilis are presented in context. The areas I personally investigated, namely, sigma factors and stationary phase functions, are also presented. L. monocytogenes and L. innocua both possess surprisingly few sigma factors: SigA, SigB, SigH, SigL, and an extra-cytoplasmic function type sigma factor (SigECF). The stationary phase genes of L. monocytogenes is compared to the well-studied, complex, stationary phase networks of B. subtilis. This showed that while genetic competence functions may be operative in unknown circumstances, non-sporulating Listeria opted for very different approaches of regulation from B. subtilis. There is virtually no overlap of known, stationary phase genes between Listeria and Gram negative model organism E. coli.
Cofilin
(1999)
This study has identified cofilin, an actin binding protein, as a control element in the reorganization of the actin cytoskeleton which is highly relevant for T lymphocyte activation. Cofilin is regulated in its activity by reversible phosphorylation which is inducible by stimulation through accessory receptors such as CD2 and CD28. First it could be demonstrated that accessory receptor triggering induces the transient association of cofilin with the actin cytoskeleton and that only the dephosphorylated form of cofilin possesses the capacity to bind cytoskeletal actin in vivo. PI3-kinase inhibitors block both the dephosphorylation of cofilin and its association with the actin cytoskeleton. Importantly, cofilin, actin, PI3-kinase and one of its substrates, namely phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2) which can bind to cofilin, co-localize within CD2-receptor caps. The cofilin/F-actin interaction has been identified as a crucial regulatory element for receptor cap formation and the strength of signal transduction. To this end, appropriately designed cell permeable non-toxic peptides that are homologous to actin binding motifs of the human cofilin sequence were introduced into untransformed human peripheral blood T lymphocytes. These peptides competitively and dose dependently inhibit the activation induced interaction of cofilin with the actin cytoskeleton in vivo. By this approach it was possible to study, for the first time, the functional consequences of this interaction in immunocompetent T cells. The present data demonstrate that inhibition of the actin/cofilin interaction in human T lymphocytes by means of these cofilin derived peptides abolishes receptor cap formation and strongly modulates functional T cell responses such as T cell proliferation, interleukin-2 production, cell surface expression of CD69, gIFN production, and CD95L expression. Importantly, receptor independent activation by PMA and calcium ionophore circumvents these peptide produced inhibitory effects on lymphocyte stimulation and places the cofilin/actin interaction to a proximal step in the cascade of signaling events following T cell activation via surface signals. The present results are novel since as yet no information existed regarding the molecular elements which link cell surface receptor stimulation directly to the resulting reorganization of the actin cytoskeleton.
Distinct juvenile behaviour differences, changes in adult sizes and reproductive capacity and a long reproductive period triggered the working hypothesis of two alternative life-cycle strategies favouring aestivation or immediate reproduction. The hypothesis for the life-cycles of Hyperolius nitidulus that differed from the commonly assumed reproductive strategy for this species was confirmed by the results of this study. Aestivated juveniles start to mature at the beginning of the rainy season and reproduce subsequently. Their tadpoles grow until metamorphosis and either reproduce in this same season, in which case their offspring aestivates (one year - two generations), or they delay reproduction to the following year and aestivate themselves (one year - one generation). Juveniles trying to reproduce as fast as possible will invest in growth and differentiation and show no costly adaptations to aestivation, while juveniles delaying reproduction to the following rainy season will be well adapted to dry season conditions. Indirect evidence for the existence of a second generation was found in all three investigation years: adult size decreased abruptly towards the end of the rainy season, mainly due to the arrival of very small individuals, and clutch size decreased abruptly. Also at the end of the rainy season juveniles had two behavioural types: one hiding on the ground and clearly avoiding direct sunlight and another sitting freely above ground showing higher tolerance towards dry season conditions (high air temperatures and low humidity). Skin morphology differed between the types showing many more purine crystals in a higher order in the dry-season adapted juveniles. The final proof for the existence of a second generation came with the recapture of individuals marked as juveniles when they left the pond. The 45 recaptured frogs definitely came back to the pond to reproduce during the same season in 1999. Second generation frogs (males and females) were significantly smaller than the rest of all adults and egg diameter was reduced. Clutch size did not differ significantly. It was found that females did not discriminate against second generation males when coming to the ponds to reproduce. Second generation males had a similar chance to be found in amplexus as first generation males. Indirect and direct evidence for a second generation matched very well. The sudden size decrease in adults occurred just at the time when the first marked frogs returned. The observation that freshly metamorphosed froglets were able to sit in the sun directly after leaving the water led to the assumption that the decision whether to aestivate or to reproduce already happens during the frogs' larval period. Water chemistry and the influence of light was investigated to look for the factors triggering the decision, but only contaminated water increased the number of juveniles ready for aestivation. Whether the life history polymorphism observed in Hyperolius nitidulus is due to phenotypic plasticity or genetic polymorphism is still not known. Despite this uncertainty, there is no doubt that the optimal combination of different life histories is profitable and may be a reason for the wide range and high local abundance of Hyperolius nitidulus.
The study examines the sensory ecology of CO2 perception in leaf-cutting ants. It begins with the ecological role of CO2 for leaf-cutting ants. Inside the subterranean nests of Atta vollenweideri large amounts of CO2 are produced by the ants and their symbiotic fungus. Measurements in field nest at different depths revealed that CO2 concentrations do not exceed 2 per cent in mature nests. These findings indicate effective ventilation even at depths of 2 m. Small colonies often face the situation of reduced ventilation when they close their nest openings as a measure against flooding. A simulation of this situation in the field as well as in the laboratory revealed increasing CO2 concentrations causing reduced colony respiration which ultimately might limit colony success. Wind-induced ventilation is the predominant ventilation mechanism of the nests of Atta vollenweideri, shown by an analysis of external wind and airflow in the channels. The mound architecture promotes nest ventilation. Outflow channels have their openings in the upper, central region and inflow channels had their openings in the lower, peripheral region of the nest mound. Air is sucked out through the central channels, followed by a delayed inflow of air through the peripheral channels. The findings support the idea that the nest ventilation mechanism used by Atta vollenweideri resembles the use of Bernoulli’s principle in Venturi Tubes and Viscous Entrainment. CO2 is important in a second context besides microclimatic control. A laboratory experiment with Atta sexdens demonstrated that leaf-cutting ants are able to orientate in a CO2 gradient. Foragers chose places with higher CO2 concentration when returning to the nest. This effect was found in all homing foragers, but it was pronounced for workers carrying leaf fragments compared to workers without leaf fragments. The findings support the hypothesis that CO2 gradients are used as orientation cue inside the (dark) nest to find suited fungus chambers for unloading of the leaf fragments. After the importance of CO2 in the natural history of the ants has thus been demonstrated, the study identifies for the first time in Hymenoptera type and location of the sensory organ for CO2 perception. In Atta sexdens a single neuron associated with the sensilla ampullacea was found to respond to CO2. Since it is the only neuron of this sensillum, the sensillum characters can be assumed to be adapted for CO2 perception. A detailed description of the morphology and the ultrastructure allows a comparison with sensilla for CO2 perception found in other insects and provides more information about sensillum characters and their functional relevance. The CO2 receptor cells respond to increased CO2 with increased neural activity. The frequency of action potentials generated by the receptor cell shows a phasic-tonic time course during CO2 stimulation and a reduced activity after stimulation. Phasic response accomplished with a reduced activity after stimulation results in contrast enhancement and the ability to track fast fluctuations in CO2 concentration. The neurons have a working range of 0 to 10 per cent CO2 and thus are able to respond to the highest concentrations the ants might encounter in their natural environment. The most exciting finding concerning the receptor cells is that the CO2 neurons of the leaf-cutting ants do not adapt to continuous stimulation. This enables the ants to continuously monitor the actual CO2 concentration of their surroundings. Thus, the sensilla ampullacea provide the ants with the information necessary to orientate in a CO2 gradient (tracking of fluctuations) as well as with the necessary information for microclimatic control (measuring of absolute concentrations).
The identification of NRAGE
(2001)
The inhibitor of apoptosis proteins (IAPs) have been shown to interact with a growing number of intracellular proteins and signalling pathways in order to fulfil their anti-apoptotic role. In order to investigate in detail how the avian homologue ITA interfered with both TNF induced apoptosis and the NGF mediated differentiation in PC12 cells, a two hybrid screen was performed with a PC12 library using ITA as a bait. The screen resulted in the identification of several overlapping fragments of a previously unknown gene. The complete cDNA for this gene was isolated, the analysis of which revealed a high homology with a large family of tumour antigens known as MAGE (melanoma associated antigens). This newly identified member of the MAGE family, which was later named NRAGE, exhibited some unique characteristics that suggested for the first time a role in normal cellular physiology for this protein family. MAGE proteins are usually restricted in their expression to malignant or tumour cells, however NRAGE was also expressed in terminally differentiated adult tissue. NRAGE also interacted with the human XIAP in direct two-hybrid tests. The interactions observed in yeast cells were confirmed in mammalian cell culture, employing both coimmunoprecipitation and mammalian two-hybrid methods. Moreover, the results of the coimmunoprecipitation experiments indicated that this interaction requires the RING domain. The widely studied 32D cell system was chosen to investigate the effect of NRAGE on apoptosis. NRAGE was stably transduced in 32D cells, and found to augment cell death induced by the withdrawal of Interleukin-3. One reason for this reduced cell viability in NRAGE expressing cells could be the binding of endogenous XIAP, which occurred inducibly after growth factor withdrawal. Interestingly, NRAGE was able to overcome the protection afforded to 32D cells by the exogenous expression of human Bcl-2. Thus NRAGE was identified during this research doctorate as a novel pro-apoptotic, IAP-interacting protein, able to accelerate apoptosis in a pathway independent of Bcl-2 cell protection.
Cardiovascular disease is the leading cause of mortality in both men and women in the Western world. Earlier observations have pointed out that pre-menopausal women have a lower risk of developing cardiovascular disease than age-matched men, with an increase in risk after the onset of menopause. This observation has directed the attention to estrogen as a potential protective factor in the heart. So far the focus of research and clinical studies has been the vascular system, leaving the current knowledge on the role of estrogen in the myocardium itself rather scarce. Functional estrogen receptor-alpha as well as -beta have recently been identified in the myocardium, making the myocardium an estrogen target organ. The focus of this thesis was 1) to investigate the role of estrogen and estrogen receptors in modulating myocardial gene expression both in vivo in an animal model for cardiac hypertrophy (spontaneously hypertensive rats; SHR), as well as in vitro in isolated neonatal cardiomyocytes, 2) to investigate the mechanisms of the rapid induction of an estrogen target gene, the early growth response gene-1 (Egr-1) and 3) to initiate the search for novel estrogen target genes in the myocardium. 1) The effects of estrogen on the expression of one of the major myocardial specific contractile proteins, the alpha-myosin heavy chain (alpha-MHC) have been investigated. In ovarectomised animals treated either with 17beta-estradiol alone or in combination with a specific estrogen receptor antagonist, ICI 182780, it was shown that both alpha-MHC mRNA and protein were upregulated by estrogen in an estrogen receptor specific manner. The in vivo results were confirmed in vitro in isolated neonatal cardiomyocytes which showed that estrogen has a direct action on the myocardium potent enough to upregulate the expression of alpha-MHC. Furthermore it was shown that the alpha-MHC promoter is induced by estrogen in an estrogen receptor-dependent manner and first investigations into the mechanisms involved in this upregulation identified Egr-1 as a potential transcription factor which, upon induction by estrogen, drives the expression of the alpha-MHC promoter. 2) Previously it was shown that Egr-1 is rapidly induced by estrogen in an estrogen receptor-dependent manner which was mediated via 5 serum response elements (SREs) in the promoter region and surprisingly not via the estrogen response elements (EREs). In this study it was shown that estrogen-treatment of cardiomyocytes resulted in the recruitment of serum response factor (SRF), or an antigenically related protein, to the SREs in the Egr-1 promoter, which was specifically inhibited by the estrogen receptor antagonist ICI 182780. Transfection experiments showed that estrogen induced a heterologous promoter consisting only of 5 tandem repeats of the c-fos SRE in an ER-dependent manner, which identified SREs as promoter elements able to confer an estrogen response to target genes. 3) Potentially new target genes regulated by estrogen in vivo were analysed using hearts of ovarectomised animals as well as ovarectomised animals treated with estrogen. Analyses of cDNA microarray filters containing 1250 known genes identified 24 genes that were modified by estrogen in vivo. Among these genes, some might have potentially important functions in the heart and further analyses of these genes will create a more global picture of the role and function of estrogen in the myocardium. Taken together, the results showed that estrogen does have a direct action on the myocardium both by regulating the expression of myocardial specific genes in vivo, as well as exerting rapid non-nuclear effects in cardiac myocytes. It was shown that SREs in the promoter region of genes can confer an estrogen response to genes identifying SREs as important elements in regulation of genes by estrogen. Furthermore, 24 potentially new estrogen targets were identified in the myocardium, contributing to the general understanding of estrogen action in the myocardium.