Narrowband multispectral filter set for visible band.

We design, fabricate and characterise a narrowband Fabry-Pérot multispectral filter set for the visible range (400-750 nm) that is suitable for integration onto complementary-metal oxide-semiconductor image sensors. We reduce the fabrication steps by fixing the physical cavity length and altering the effective optical length instead. Using electron-beam lithography, a sub-wavelength hole array is patterned in a silicon nitride cavity layer, backfilled with poly(methyl methacrylate), and bounded by aluminium mirrors to create 23 filters with full-width half-maximums of 22-46 nm. Additionally, for colourmetric reproduction applications, using as few as 10 filters gives a colour difference (CIEDE2000) of 0.072, better than trichromatic filters.

Performance analysis of an orbital angular momentum multiplexed amplify-and-forward radio relay chain with inter-modal crosstalk.

The end-to-end spectral efficiency and bit error rate (BER) of an amplify-and-forward (AF) radio relay chain employing orbital angular momentum (OAM) multiplexing is presented. The inherent divergence of a beam carrying OAM is overcome by means of a lens. Modelled and measured inter-modal crosstalk levels are incorporated into the analysis. The results show that an end-to-end spectral efficiency of up to 8 bits s-1 Hz-1 is achievable using four OAM modes to multiplex four parallel data streams over 20 hops, provided that the detrimental effects of inter-modal crosstalk are mitigated. The spectral efficiency is expected to scale further by using more OAM modes. The BER profile along the relay chain is analysed for each of the four OAM modes.

Experimental evaluation of 3D printed spiral phase plates for enabling an orbital angular momentum multiplexed radio system.

This paper evaluates the performance of three-dimensionally (3D) printed spiral phase plates (SPPs) for enabling an orbital angular momentum (OAM) multiplexed radio system. The design and realization of the SPPs by means of additive manufacturing exploiting a high-permittivity material is described. Modes 1 and 2 SPPs are then evaluated at 15 GHz in terms of 3D complex radiation pattern, mode purity and beam collimation by means of a 3D printed dielectric lens. The results with the lens yield a crosstalk of -8 dB for between modes 1 and -1, and -11.4 dB for between modes 2 and -2. We suggest a mode multiplexer architecture that is expected to further reduce the crosstalk for each mode. An additional loss of 4.2 dB is incurred with the SPPs inserted into the communication link, which is undesirable for obtaining reliable LTE-based communications. Thus, we suggest: using lower loss materials, seeking ways to reduce material interface reflections or alternative ways of OAM multiplexing to realize a viable OAM multiplexed radio system.

Probing microwave fields and enabling in-situ experiments in a transmission electron microscope.

A technique is presented whereby the performance of a microwave device is evaluated by mapping local field distributions using Lorentz transmission electron microscopy (L-TEM). We demonstrate the method by measuring the polarisation state of the electromagnetic fields produced by a microstrip waveguide as a function of its gigahertz operating frequency. The forward and backward propagating electromagnetic fields produced by the waveguide, in a specimen-free experiment, exert Lorentz forces on the propagating electron beam. Importantly, in addition to the mapping of dynamic fields, this novel method allows detection of effects of microwave fields on specimens, such as observing ferromagnetic materials at resonance.

Measured and simulated performance of a ceramic micromechanical beam steering device at 94 GHz.

We report the first experimental demonstration of a transmission-mode micromechanical beam steering device for use in standoff terahertz imaging and spectroscopy. The device was constructed by laminating laser-cut 96% alumina sheets to form two plates with interlocking rectangular gratings of 762 microm period and was characterized at 94 GHz in a free-space measurement setup with an automated elevation scan. Plate tilts as great as 6 degrees deflected the transmitted beam by 6 degrees for the transverse electric (TE) polarization and by 4 degrees for the transverse magnetic polarization. Finite-difference time-domain simulations of the TE performance were in good agreement with the measurements.

Mice transgenic for a human porcine endogenous retrovirus receptor are susceptible to productive viral infection.

Porcine endogenous retrovirus (PERV) is considered one of the major risks in xenotransplantation. No valid animal model has been established to evaluate the risks associated with PERV transmission to human patients by pig tissue xenotransplantation or to study the potential pathogenesis associated with PERV infection. In previous work we isolated two genes encoding functional human PERV receptors and proved that introduction of these into mouse fibroblasts allowed the normally nonpermissive mouse cells to become productively infected (T. A. Ericsson, Y. Takeuchi, C. Templin, G. Quinn, S. F. Farhadian, J. C. Wood, B. A. Oldmixon, K. M. Suling, J. K. Ishii, Y. Kitagawa, T. Miyazawa, D. R. Salomon, R. A. Weiss, and C. Patience, Proc. Natl. Acad. Sci. USA 100:6759-6764, 2003). In the present study we created mice transgenic for human PERV-A receptor 2 (HuPAR-2). After inoculation of transgenic animals with infectious PERV supernatants, viral DNA and RNA were detected at multiple time points, indicating productive replication. This establishes the role of HuPAR-2 in PERV infection in vivo; in addition, these transgenic mice represent a new model for determining the risk of PERV transmission and potential pathogenesis. These mice also create a unique opportunity to study the immune response to PERV infection and test potential therapeutic or preventative modalities.

Inductive events in the patterning of the Xenopus laevis hatching and cement glands, two cell types which delimit head boundaries.

In Xenopus, the hatching and cement glands form at important boundaries in the head. We have examined induction of these glands in order to see the basis for this ectodermal patterning. Ectoderm can be induced to form hatching and cement glands by dorsal mesoderm and by the neural plate. Because the neural plate is sufficient to induce hatching and cement glands and lies adjacent to presumptive hatching and cement glands at the time of induction, it is the best candidate for the in vivo inducer of these tissues. The cement gland is restricted to the front of the head in part because the anterior but not posterior neural plate is capable of inducing it. The hatching gland is also restricted to the head, but can be induced by both anterior and posterior neural plates. Therefore, some factor suppresses hatching gland differentiation in the trunk. Transplanted neural plate pieces induced hatching gland cells in the ectoderm of embryos, suggesting that the inductive signal is planar. Treatment with retinoic acid or lithium at the start of gastrulation caused a loss of head structures. The presence of hatching gland in lithium-treated embryos suggests that these two agents have distinct effects and supports the idea that the induction of hatching and cement glands involves different pathways.

Development of the Xenopus laevis hatching gland and its relationship to surface ectoderm patterning.

An antibody that recognizes tyrosine hydroxylase can be used as a marker for hatching gland cells in Xenopus embryos. Using this marker, we have shown that hatching gland cells are induced at the end of gastrulation and that presumptive hatching gland cells are localized to the anterior neural folds in Xenopus. The movements of neurulation bring the hatching gland cells together to form a characteristic Y pattern on the dorsoanterior surface of the head. The Y pattern delineates several zones of surface ectoderm which can be visualized by the presence or absence of ciliated cells. As development proceeds the hatching gland pattern is altered, demonstrating the active changes involved in forming the face. Lithium, UV irradiation and retinoic acid can be used to alter the hatching gland pattern in specific ways which help to understand the underlying mechanisms of ectodermal patterning.

Effects of localized application of retinoic acid on Xenopus laevis development.

In order to more accurately determine the mechanism by which retinoic acid causes embryonic defects, we have developed a simple method of locally applying retinoic acid rather than immersing the whole embryo in retinoic acid solutions. Retinoic acid was suspended in corn oil and then injected between the surface and the deep ectodermal layers of an early gastrula Xenopus embryo. When droplets containing retinoic acid were injected into the presumptive head region, the embryos exhibited inhibited development of anterior structures near the injection site. Development of the eye, cement gland, hatching gland, olfactory pits, and expression of engrailed protein were all disrupted near the injection site. Inhibited development of anterior structures was far greater on the injected side of the embryo than on the uninjected side. The retinoic acid droplet did not cause an anterior shift of structures on the injected side relative to the uninjected side. These experiments suggest that retinoic acid does not cause global respecification of axial level in the head, but rather suppresses development of anterior structures. Retinoic acid injected into presumptive trunk regions had no discernible effect.

Experimental erosion of dentin.

Experimental erosion in human dentin was investigated with scanning electron microscopy. Erosion was caused by solutions containing either 0.030 mekV/g malic acid (pH 3.4), 0.034 mekV/g phosphoric acid (pH 2.6), or 0.038 mekV/g citric acid (pH 2.8). Test specimens prepared from the coronal parts of erupted third molars were immersed in the solutions from 30 s to 60 min. When compared with controls, exposure of dentin tubules was observed in all the specimens already after 30 s immersion, irrespective of the acid used. Mineral loss was seen to progress at the interface between peritubular and intertubular dentin in specimens immersed for 60 s in the acidic solutions. Longer times of immersion resulted in hollowing of the tubular openings by complete destruction of the peritubular dentin. Surface roughness and porosities were seen also at the intertubular areas. Although based on a simplified study model, our results may explain why so many patients with erosions suffer from painful sensitivity of their teeth: the acids causing erosion can expose inner dentin structures to outer stimuli by significant enlargement of the dentinal tubules.

Embryonic origins of spleen asymmetry.

The spleen is a vertebrate organ that has both hematopoietic and immunologic function. The embryonic origins of the spleen are obscure, with most studies describing the earliest rudiment of the spleen as a condensation of mesodermal mesenchyme on the left side of the dorsal mesogastrium. The development of spleen handedness has not been described previously, presumably because of the difficulty in assaying spleen position in the embryo and the lack of early, organ-specific molecular markers. Here we show that expression of the homeobox gene Nkx2-5 serves as a marker for spleen precursor tissue. Pre-splenic tissue is initially located in symmetric domains on both sides of the embryo but, during subsequent development, only the left side goes on to form the mature spleen. Therefore, the final location of the spleen on the left side of the body axis appears to result from preferential development of the spleen precursor cells on the left side of the embryo. Our studies indicate that the spleen and heart become asymmetric via different cellular mechanisms. Nkx2-5 may function locally as part of the laterality cascade, downstream of nodal and Pitx2, or it may direct asymmetric morphogenesis after laterality has been determined.

A role for GATA-4/5/6 in the regulation of Nkx2.5 expression with implications for patterning of the precardiac field.

Interactions between the key regulatory genes of the cardiogenic pathway, including those from the GATA and Nkx2 transcription factor families, are not well defined. Treating neurula-stage Xenopus embryos with retinoic acid (RA) causes a specific block in cardiomyocyte development that correlates with a progressive reduction in the region of the presumptive heart-forming region expressing Nkx2.5. In contrast, RA does not block expression of the GATA-4/5/6 genes, which are transcribed normally in an overlapping pattern with Nkx2.5 throughout cardiogenesis. Instead, GATA-4/5/6 transcription levels are increased, including an expansion of the expression domain corresponding to lateral plate mesoderm that is part of the early heart field, but that normally is progressively restricted in its ability to contribute to the myocardium. GATA-dependent regulatory sequences of the Nkx2.5 gene that implicate GATA-4/5/6 as upstream positive regulators were described recently. However, our experiments also indicate that GATA factors might normally antagonize transcription of Nkx2.5. To test this hypothesis we generated a dominant negative isoform of GATA-4 (SRG4) capable of inhibiting transcription of GATA-dependent target genes. Ectopic expression of SRG4 results in a transient expansion of the Nkx2.5 transcript pattern, indicating that a normal function of GATA factors is to limit the boundary of the Nkx2.5 expression domain to the most anterior ventral region of the heart field. Regulatory mechanisms altered by excess RA must function normally to limit GATA-4/5/6 expression levels, to define the region of Nkx2.5 expression and regulate myocardial differentiation.

Retinoic acid can block differentiation of the myocardium after heart specification.

While a number of transcription factors that are likely to play a role in cardiac differentiation have recently been described, the signals that lead to the expression of these factors remains poorly understood. Here we report that exposure of Xenopus embryos to continuous low levels of all-trans retinoic acid (RA), starting at the time of neural fold closure, blocks expression of myocardial differentiation markers. The development of the remainder of the embryo is relatively normal, suggesting that retinoic acid can act rather specifically on myocardial precursors. Indeed, the pattern of endocardial gene expression appears to remain unaffected by RA treatment. Although RA blocks myocardial gene expression, a superficially normal heart tube forms. The heart tube, however, fails to loop during subsequent development and never forms beating tissue. The effect of RA treatment on expression of myocardial genes is developmental stage dependent, since no influence is observed after myocardial differentiation has commenced. These data indicate that a vital component of the myocardial determination pathway is sensitive to retinoid signaling.

Differences in arachidonic acid metabolism and effects of aspirin between one- and two-kidney Goldblatt hypertensive rats.

Vasodepressor responses to prostacyclin, nitroprusside and arachidonic acid were compared in two groups of anaesthetized, two-kidney, one-clip Goldblatt rats. The groups were composed of rats which had high blood pressure (greater than 150 mmHg systolic) or normal blood pressure (less than 140 mmHg systolic). The vasodepressor effects of prostacyclin and nitroprusside and arachidonic acid did not differ significantly between hypertensive and normotensive groups when measured as percentages of resting blood pressure. Thus, in contrast to one-kidney Goldblatt hypertensive rats, there is no evidence for increased vascular conversion of arachidonic acid to prostacyclin in the two-kidney hypertensive model. The effect of cyclo-oxygenase inhibition on development of hypertension in one- and two-kidney Goldblatt rats was also studied by treating them daily with aspirin (200 mg/kg orally) from 3 days before until 3 weeks after clipping the renal artery. Aspirin-treated two-kidney rats developed significantly higher blood pressures than vehicle-treated controls, but the blood pressures of aspirin-treated one-kidney rats increased less after clipping than those of vehicle-treated controls. It appears paradoxical that transformation of arachidonic acid to prostacyclin is increased, while aspirin has a blood pressure lowering effect in one-kidney Goldblatt rats. It is suggested that there might be a more fundamental disturbance in arachidonate metabolism in hypertension which might contribute to increased vascular reactivity.

Increased conversion of arachidonic acid to vasodilator prostanoids in spontaneously hypertensive rats.

1. Vasodepressor responses to intravenous injection of prostacyclin, arachidonic acid, and nitroprusside were examined in anaesthetized, spontaneously hypertensive rats (SHR) of the Okamoto strain, and in their normotensive Wistar-Kyoto (WKY) controls. 2. Depressor responses to prostacyclin and nitroprusside did not differ significantly between the two strains. 3. The vasodepressor effects of arachidonic acid were greater and much more prolonged in SHR than in WKY. In rats treated with indomethacin (2 mg/kg) arachidonic acid induced only transient depressor responses which did not differ significantly between these strains. 4. It is concluded that SHR do not differ from WKY in their sensitivity to prostacyclin but they have enhanced ability to transform exogenous arachidonic acid into vasodilator prostanoids.

Vasodepressor effects of arachidonic acid and prostacyclin (PGI2) in hypertensive rats.

1. Vasodepressor responses to prostacyclin and nitroprusside were compared in anaesthetized, spontaneously hypertensive rats of the Okamoto strain and Wistar--Kyoto controls, and also in one-kidney, one-clip hypertensive rats and unilaterally nephrectomized controls of the Sprague--Dawley strain. The responses, measured as a percentage of resting blood pressure, did not differ significantly between the hypertensive rats and the normotensive controls within each strain. 2. The effects of intravenous injections of arachidonic acid were also studied in each strain. 3. The vasodepressor effects of high doses of arachidonic acid (1 or 3 mg/kg) were much greater and more prolonged in both groups of hypertensive rats. These differences were abolished by indomethacin (2 mg/kg). 4. Comparisons between the strains showed that whereas Okamoto rats have significantly greater depressor responsiveness to nitroprusside and prostacyclin than Sprague--Dawley rats, the depressor effects of high doses of arachidonic acid (1 and 3 mg/kg) were smaller in the normotensive Wistar--Kyoto than in the Sprague--Dawley rats. 5. It is concluded that hypertensive rats have enhanced ability to transform exogenous arachidonic acid into vasodilator prostanoids. This occurs both in spontaneous hypertension and in experimental renal hypertension. However, rats of the Okamoto strain appear to have reduced ability to form prostacyclin when compared with Sprague--Dawley rats.

XNkx-2.5, a Xenopus gene related to Nkx-2.5 and tinman: evidence for a conserved role in cardiac development.

We have isolated a Xenopus homeodomain sequence, XNkx-2.5, which shows significant similarity to mouse Nkx-2.5 and to the Drosophila tinman gene product. In Drosophila, tinman is required for formation of the heart and visceral mesoderm structures. In situ hybridization studies show that XNkx-2.5 is expressed in the heart region during early Xenopus development and later is also expressed in gut tissue. The observed similarity of sequences and expression patterns suggests that the regulatory mechanisms underlying heart formation may be conserved between distant species.

Cardiac troponin I is a heart-specific marker in the Xenopus embryo: expression during abnormal heart morphogenesis.

Cardiac troponin I (troponin Ic) expression is restricted to the heart at all stages of Xenopus development. Whole-mount in situ hybridization and Northern blot analysis indicates that troponin Ic is first expressed in tailbud embryos (stage 28) about the time of the first cytological heart differentiation and about 24 hr before beating tissue is observed. We have used this marker to examine abnormal heart morphogenesis in embryos treated with retinoic acid and lithium. When retinoic acid is administered to embryos prior to heart specification, heart tissue is reduced and often completely ablated. When embryos are treated after heart specification, but before the heart primordium migrates to the ventral midline, the migration is unaffected but smaller, abnormal hearts result. Lithium treatment of cleavage stage embryos causes an increase in heart tissue. In severely dorsalized embryos, heart tissue can be found around the entire embryo with the exception of a small gap at the most dorsal point. This gap indicates that migration of the heart to the ventral midline does not occur in these embryos. Later in development, a centrally located, beating heart is observed in dorsalized embryos. The timing of its appearance suggests that it is formed by movements normally associated with heart morphogenesis rather than migration.

Molecular cloning and functional characterization of inhibitor-sensitive (mENT1) and inhibitor-resistant (mENT2) equilibrative nucleoside transporters from mouse brain.

Mammalian cells express at least two subtypes of equilibrative nucleoside transporters, i.e. ENT1 and ENT2, which can be distinguished functionally by their sensitivity and resistance respectively to inhibition by nitrobenzylthioinosine. The ENT1 transporters exhibit distinctive species differences in their sensitivities to inhibition by dipyridamole, dilazep and draflazine (human>mouse>rat). A comparison of the ENT1 structures in the three species would facilitate the identification of the regions involved in the actions of these cardioprotective agents. We now report the molecular cloning and functional expression of the murine (m)ENT1 and mENT2 transporters. mENT1 and mENT2 encode proteins containing 458 and 456 residues respectively, with a predicted 11-transmembrane-domain topology. mENT1 has 88% and 78% amino acid identity with rat ENT1 and human ENT1 respectively; mENT2 is more highly conserved, with 94% and 88% identity with rat ENT2 and human ENT2 respectively. We have also isolated two additional distinct cDNAs that encode proteins similar to mENT1; these probably represent distinct mENT1 isoforms or alternative splicing products. One cDNA encodes a protein with two additional amino acids (designated mENT1b) that adds a potential protein kinase CK2 phosphorylation site in the central intracellular loop of the transporter, and is similar, in this regard, to the human and rat ENT1 orthologues. The other cDNA has a 5'-untranslated region sequence that is distinct from that of full-length mENT1. Microinjection of mENT1, mENT1b or mENT2 cRNA into Xenopus oocytes resulted in enhanced uptake of [(3)H]uridine by the oocytes relative to that seen in water-injected controls. mENT1-mediated, but not mENT2-mediated, [(3)H]uridine uptake was inhibited by nitrobenzylthioinosine and dilazep. Dipyridamole inhibited both mENT1 and mENT2, but was significantly more effective against mENT1. Adenosine inhibited both systems with a similar potency, as did a range of other purine and pyrimidine nucleosides. These results are compatible with the known characteristics of the native mENT1 and mENT2 transporters.