Structural engineering from an inverse problems perspective

The field of structural engineering is vast, spanning areas from the design of new infrastructure to the assessment of existing infrastructure. From the onset, traditional entry-level university courses teach students to analyse structural responses given data including external forces, geometry, member sizes, restraint, etc.-characterizing a forward problem (structural causalities → structural response). Shortly thereafter, junior engineers are introduced to structural design where they aim to, for example, select an appropriate structural form for members based on design criteria, which is the inverse of what they previously learned. Similar inverse realizations also hold true in structural health monitoring and a number of structural engineering sub-fields (response → structural causalities). In this light, we aim to demonstrate that many structural engineering sub-fields may be fundamentally or partially viewed as inverse problems and thus benefit via the rich and established methodologies from the inverse problems community. To this end, we conclude that the future of inverse problems in structural engineering is inexorably linked to engineering education and machine learning developments.

Anaphylactic reaction to hydroxyzine in an anesthetized patient

A case of anaphylaxis occurring during a general anesthesia is presented. The reaction was severe with bronchospasm and hypotension (grade 2 in the severity of per-operative anaphylactic shock). The responsibility of hydroxyzine, administered for premedication was suspected by intradermal testing with the molecule, which was twice positive at a 10(-2) dilution of the commercial solution. The same test remained negative in 5 control subjects. All the other drugs received during anesthesia gave negative results. Using the same protocol excepted for the use of hydroxyzine a new general anesthesia could be performed under a premedication with dexchlorpheniramine without any allergic reaction. Anaphylactic reactions are very rare with hydroxyzine used in premedication for anesthesia in regard to the large prescription of the drug. Only two previous cases were reported but attention of the allergist must be also pointed towards the medications received in the perioperative period as for the anesthetic drugs.

Cubitus interruptus-independent transduction of the Hedgehog signal in Drosophila

The Hedgehog (Hh) family of secreted proteins are key factors that control pattern formation in invertebrates and vertebrates. The manner in which Hh molecules regulate a target cell remains poorly understood. In the Drosophila embryo, Hh is produced in identical stripes of cells in the posterior compartment of each segment. From these cells a Hh signal acts in both anterior and posterior directions. In the anterior cells, the target genes wingless and patched are activated whereas posterior cells respond to Hh by expressing rhomboid and patched. Here, we have examined the role of the transcription factor Cubitus interruptus (Ci) in this process. So far, Ci has been thought to be the most downstream component of the Hh pathway capable of activating all Hh functions. However, our current study of a null ci allele, indicates that it is actually not required for all Hh functions. Whereas Hh and Ci are both required for patched expression, the target genes wingless and rhomboid have unequal requirements for Hh and Ci activity. Hh is required for the maintenance of wingless expression before embryonic stage 11 whereas Ci is necessary only later during stage 11. For rhomboid expression Hh is required positively whereas Ci exhibits negative input. These results indicate that factors other than Ci are necessary for Hh target gene regulation. We present evidence that the zinc-finger protein Teashirt is one candidate for this activity. We show that it is required positively for rhomboid expression and that Teashirt and Ci act in a partially redundant manner before stage 11 to maintain wingless expression in the trunk.

The role of Teashirt in proximal leg development in Drosophila: ectopic Teashirt expression reveals different cell behaviours in ventral and dorsal domains

Localised transcription factors specify the identity of developmental domains. Here we analyse the function of the Teashirt zinc finger protein, which is expressed in the proximal domain of the Drosophila leg. By ectopic expression of a teashirt transgene we show that Teashirt contributes to the differences in cell-cell adhesion between proximal and distal leg cells. Whereas clones of cells expressing the teashirt transgene survive in the endogenous Teashirt domain, most cells expressing Teashirt in an ectopic distal position are lost from the epithelium. In clones which were recovered in the distal domain, different effects were seen dependent on position with respect to the dorsal-ventral axis. In the ventral region, where Wingless is signalling, surviving clones express Teashirt and cause abnormalities in the adult leg. Contrarily, lateral and dorsal clones generally do not accumulate Teashirt and have no effect on patterning. One exception to the differential dorsal-ventral effects occurs at the boundary between Teashirt-expressing and -nonexpressing cells. Both ectopic and hypomorphic loss of teashirt affects patterning at all positions at the boundary, suggesting that Teashirt plays a crucial role in boundary formation. The results are discussed with respect to the roles of transcriptional and posttranscriptional mechanisms in proximal-distal axis patterning of the Drosophila legs.

Differential requirements of the fused kinase for hedgehog signalling in the Drosophila embryo

The two signalling proteins, Wingless and Hedgehog, play fundamental roles in patterning cells within each metamere of the Drosophila embryo. Within the ventral ectoderm, Hedgehog signals both to the anterior and posterior directions: anterior flanking cells express the wingless and patched Hedgehog target genes whereas posterior flanking cells express only patched. Furthermore, Hedgehog acts as a morphogen to pattern the dorsal cuticle, on the posterior side of cells where it is produced. Thus responsive embryonic cells appear to react according to their position relative to the Hedgehog source. The molecular basis of these differences is still largely unknown. In this paper we show that one component of the Hedgehog pathway, the Fused kinase accumulates preferentially in cells that could respond to Hedgehog but that Fused concentration is not a limiting step in the Hedgehog signalling. We present direct evidence that Fused is required autonomously in anterior cells neighbouring Hedgehog in order to maintain patched and wingless expression while Wingless is in turn maintaining engrailed and hedgehog expression. By expressing different components of the Hedgehog pathway only in anterior, wingless-expressing cells we could show that the Hedgehog signalling components Smoothened and Cubitus interruptus are required in cells posterior to Hedgehog domain to maintain patched expression whereas Fused is not necessary in these cells. This result suggests that Hedgehog responsive ventral cells in embryos can be divided into two distinct types depending on their requirement for Fused activity. In addition, we show that the morphogen Hedgehog can pattern the dorsal cuticle independently of Fused. In order to account for these differences in Fused requirements, we propose the existence of position-specific modulators of the Hedgehog response.

The C-terminal domain of armadillo binds to hypophosphorylated teashirt to modulate wingless signalling in Drosophila

Wnt signalling is a key pathway for tissue patterning during animal development. In Drosophila, the Wnt protein Wingless acts to stabilize Armadillo inside cells where it binds to at least two DNA-binding factors which regulate specific target genes. One Armadillo-binding protein in Drosophila is the zinc finger protein Teashirt. Here we show that Wingless signalling promotes the phosphorylation and the nuclear accumulation of Teashirt. This process requires the binding of Teashirt to the C-terminal end of Armadillo. Finally, we present evidence that the serine/threonine kinase Shaggy is associated with Teashirt in a complex. We discuss these results with respect to current models of Armadillo/beta-catenin action for the transmission of the Wingless/Wnt pathway.

Trunk-specific modulation of wingless signalling in Drosophila by teashirt binding to armadillo

BACKGROUND

One function of the Wingless signal cascade is to determine the 'naked' cuticle cell-fate choice instead of the denticled one in Drosophila larvae. Wingless stabilises cytoplasmic Armadillo, which may act in a transcriptional activator complex with the DNA-binding protein T-cell factor (also known as Pangolin). As these components are critical for all Wingless-dependent patterning events, the problem arises as to how specific outputs are achieved.

RESULTS

The Teashirt zinc finger protein was found to be necessary for a subset of late Wingless-dependent functions in the embryonic trunk segments where the teashirt gene is expressed. Teashirt was found to be required for the maintenance of the late Wingless signalling target gene wingless but not for an earlier one, engrailed. Armadillo and Teashirt proteins showed similar Wingless-dependent modulation patterns in homologous parts of each trunk segment in embryos, with high levels of nuclear Teashirt and intracellular Armadillo within cells destined to form naked cuticle. We found that Teashirt associates with, and requires, Armadillo in a complex for its function.

CONCLUSIONS

Teashirt binds to, and requires, Armadillo for the naked cell-fate choice in the larval trunk. Teashirt is required for trunk segment identity, suggesting that Teashirt provides a region-specific output to Armadillo activity. Further modulation of Wingless is achieved in homologous parts of each trunk segment where Wingless and Teashirt are especially active. Our results provide a novel, cell-intrinsic mechanism to explain the modulation of the activity of the Wingless signalling pathway.

The Drosophila teashirt homeotic protein is a DNA-binding protein and modulo, a HOM-C regulated modifier of variegation, is a likely candidate for being a direct target gene

The Drosophila teashirt (tsh) gene has an homeotic function which, in combination with HOM-C genes, determines thoracic and abdominal (trunk) identities. Analysis of TSH protein distribution during embryogenesis using a specific polyclonal antibody shows that it is nuclear. The protein is present with regional modulation in several tissues within the trunk, suggesting additional tsh functions to those already studied. We identified a candidate tsh target shared with some HOM-C genes, the modifier of variegation gene modulo (mod). The TSH zinc-finger protein recognizes in vitro two specific sites within a 5' control element of the mod gene which responds in vivo to tsh activity. TSH is therefore a DNA binding protein and might directly control mod expression.

[Multiparameter correlative study of respiratory gas exchange during exercise]

Patients with chronic heart failure were evaluated simultaneously by conventional methods and by heart-lung exploration during exercise with the purpose of validating the latter method. Only 50 patients were evaluated on two occasions and therefore included in the correlative statistical study. In this study such data as NYHA classification, cardiothoracic ratio, ejection fraction, echocardiographic fibre shortening fraction and biochemical values (venous lactate, plasma noradrenaline levels) were compared with data obtained from evaluation during exercise, i.e. VO2 max, VO2 peak, anaerobic threshold, oxygen pulse, VCO2, O2 equivalent and respiratory quotient, alveolar ventilation per minute, duration and load of exercise. Very good correlation was found with the indices obtained from VO2 and in particular with the O2 pulse and the VO2 max percentage. Good correlation was also found with VCO2 and the O2 equivalent as well as with alveolar ventilation per minute. In contrast, the anaerobic threshold and respiratory quotient correlated poorly with the first set of data and therefore were disappointing. It appears from this study that the indices obtained from VO2 are highly representative of the heart-lung unit in patients with heart failure. It seems, however, that the muscular status of the patients plays a considerable role in their exercise capacity. We suggest that these indices should be used in clinical pharmacology studies.