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In this letter, we investigate the dynamics of injection-locking a nonlinear micromechanical oscillator operating in different regimes of electromechanical nonlinearity to an external tone generated by a secondary oscillator. The micromechanical oscillator exhibits a combination of mechanical and electrostatic nonlinearities that were tuned using a bias voltage to adjust the relative importance of third-order and fifth-order stiffness nonlinearities. While it is well-known that third-order stiffness (Duffing) nonlinearity results in a synchronization range that increases with an oscillator’s amplitude, little is known about the impact of other nonlinearities. We show that when using Duffing nonlinearity cancellation, higher order nonlinearities dominate, the synchronization range is smaller but has a greater rate-of-increase with oscillation amplitude. When both mechanical stiffness-hardening and electrostatic stiffness-softening nonlinearities are present, the frequency response follows an “s-curve” and, unlike the other conditions, the synchronization range does not increase monotonically with amplitude but instead reaches a minimum when both nonlinearities have similar magnitude. We develop a nonlinear resonator model and show that this model achieves good quantitative prediction of the measured synchronization range in all nonlinear operating regimes studied. [ABSTRACT FROM AUTHOR]

Resonators used in frequency-reference oscillators must maintain a stable frequency output even when subjected to temperature variations. The traditional solution is to construct the resonator from a material with a low temperature coefficient, such as AT-cut quartz, which can achieve absolute frequency stability on the order of 625 ppm over commercial temperature ranges. In comparison, Si microresonators suffer from the disadvantage that silicon's temperature coefficient of frequency (TCF) is approximately two orders of magnitude greater than that of AT-cut quartz. In this paper, we present an in situ passive temperature compensation scheme for Si microresonators based on nonlinear amplitude-frequency coupling which reduces the TCF to a level comparable with that of an AT-quartz resonator. The implementation of this passive technique is generic to a variety of Si microresonators and can be applied to a number of frequency control and timing applications. [ABSTRACT FROM AUTHOR]

This paper presents an ultrasonic fingerprint sensor based on a 24 × 8 array of 22MHz piezoelectric micromachined ultrasonic transducers (PMUTs) with 100 lm pitch, fully integrated with 180 nm complementary metal oxide semiconductor (CMOS) circuitry through eutectic wafer bonding. Each PMUT is directly bonded to a dedicated CMOS receive amplifier, minimizing electrical parasitics and eliminating the need for through-silicon vias. The array frequency response and vibration mode-shape were characterized using laser Doppler vibrometry and verified via finite element method simulation. The array's acoustic output was measured using a hydrophone to be ~14 kPa with a 28V input, in reasonable agreement with predication from analytical calculation. Pulse-echo imaging of a 1D steel grating is demonstrated using electronic scanning of a 20 × 8 sub-array, resulting in 300mV maximum received amplitude and 5:1 contrast ratio. Because the small size of this array limits the maximum image size, mechanical scanning was used to image a 2D polydimethylsiloxane fingerprint phantom (10mm × 8mm) at a 1.2mm distance from the array. [ABSTRACT FROM AUTHOR]

This work investigates the closed-loop operation of microelectromechanical oscillators in the presence of both cubic (Duffing) nonlinearities and parametric amplification. We present a theoretical model for this system that enables us to predict oscillation amplitude and instability and experimentally verify it using a silicon disk resonator with a quality factor (Q) of 85 000 and a natural frequency of 251 kHz. We determine that, contrary to previous understanding gained from analyzing the open-loop system, the presence of cubic nonlinearities does not limit the maximum stable oscillation amplitude if the resonator is operated in a closed loop. In addition, the stability and amplitude behavior predicted by our theoretical model are independent of the presence or severity of cubic nonlinearities, or on drive amplitude. [ABSTRACT FROM AUTHOR]

This paper presents an 8 x 24 element, 100 μm-pitch, 20 MHz ultrasound imager based on a piezoelectric micromachined ultrasonic transducer (PMUT) array having integrated acoustic waveguides. The 70 im diameter, 220 μm\ long waveguides function both to direct acoustic waves and to confine acoustic energy, and also to provide mechanical protection for the PMUT array used for surface-imaging applications such as an ultrasonic fingerprint sensor. The imager consists of a PMUT array bonded with a CMOS ASIC using wafer-level conductive eutectic bonding. This construction allows each PMUT in the array to have a dedicated front-end receive amplifier, which together with on-chip analog multiplexing enables individual pixel read-out with high signal-to-noise ratio through minimized parasitic capacitance between the PMUT and the front-end amplifier. Finite element method simulations demonstrate that the waveguides preserve the pressure amplitude of acoustic pulses over distances of 600 μm\. Moreover, the waveguide design demonstrated here enables pixel-by-pixel readout of the ultrasound image due to improved directivity of the PMUT by directing acoustic waves and creating a pressure field with greater spatial uniformity at the end of the waveguide. Pulse-echo imaging experiments conducted using a one-dimensional steel grating demonstrate the array's ability to form a two-dimensional image of a target. [ABSTRACT FROM AUTHOR]

This paper presents a 3-axis Lorentz force magnetometer based on an encapsulated micromechanical silicon resonator having three orthogonal vibration modes, each measuring one vector component of the external magnetic field. One mode, with natural frequency fn) of 46.973 kHz and quality factor (Q) of 14918, is operated as a closed-loop electrostatically excited oscillator to provide a frequency reference for 3-axis sensing and Lorentz force generation. Current, modulated at the reference frequency, is injected into the resonator, producing Lorentz force that is centered at the reference frequency. Lorentz force in the first axis is nulled by the oscillator loop, resulting in force-rebalanced operation. The bandwidth and scale-factor of this force-rebalanced axis are independent of resonator Q, improving the sensor's temperature coefficient from 20 841ppm/°C to 424ppm/°C. The frequencies of the other two modes are closely spaced to the first mode's reference frequency and are demonstrated to track this frequency over temperature within 1 ppm/K. Field measurements in these two axes are conducted open-loop and off-resonance, ensuring that the scale-factor is independent of Q to first order and producing a measurement bandwidth of over 40 Hz. [ABSTRACT FROM AUTHOR]

In this paper, we explore the effects of electrostatic parametric amplification on a high quality factor (Q>100 000) encapsulated disk resonator gyroscope (DRG), fabricated in h100i silicon. The DRG was operated in the n=2 degenerate wineglass mode at 235 kHz, and electrostatically tuned so that the frequency split between the two degenerate modes was less than 100mHz. A parametric pump at twice the resonant frequency is applied to the sense axis of the DRG, resulting in a maximum scale factor of 156.6 µV/(°/s), an 8.8x improvement over the non-amplified performance. When operated with a parametric gain of 5.4, a minimum angle random walk of 0.034°/√h and bias instability of 1.15°/h are achieved, representing an improvement by a factor of 4.3°x and 1.5x, respectively. [ABSTRACT FROM AUTHOR]

We are developing a novel MEMS-magnetoresistive hybrid device aimed at ultra low magnetic field detection. The hybrid device combines magnetoresistive (MR) sensors and AlN based piezoelectric MEMS resonators. The MR sensor can achieve highly sensitive magnetic field detection but suffers from high magnetic and electrical 1/f noise, limiting its applicability for dc and low-frequency field detection. We overcome this problem by using two piezoelectric cantilevers with integrated magnetic flux concentrators (MFC) to mechanically modulate the external magnetic fields into the high frequency region where the 1/f noise in the MR device vanishes. In this paper we report our fabrication approach and preliminary characterization of the hybrid device. [ABSTRACT FROM PUBLISHER]

We present a mechanical pressing technique for generating ultra-smooth surfaces on thin metal films by flattening the bumps, asperities, rough grains and spikes of a freshly vacuum deposited metal film. The method was implemented by varying the applied pressure from 100 MPa to 600 MPa on an e-beam evaporated silver film of thickness 1000 Å deposited on double-polished (100)-oriented silicon surfaces, resulting in a varying degree of film smoothness. The surface morphology of the thin film was studied using atomic force microscopy. Notably, at a pressure of ∼600 MPa an initial silver surface with 13-nm RMS roughness was plastically deformed and transformed to an ultra-flat plane with better than 0.1 nm RMS. Our demonstration with the e-beam evaporated silver thin film exhibits the potential for applications in decreasing the scattering-induced losses in optical metamaterials, plasmonic nanodevices and electrical shorts in molecular-scale electronic devices. [ABSTRACT FROM AUTHOR]

This paper presents a Lorentz force magnetometer employing a micromechanical oscillator. The oscillator, actuated by both electrostatic force and Lorentz force, is based on a 370 μm by 230 μm silicon micromechanical resonator with quality factor (Q) of 13 000. This field-sensitive micromechanical oscillator eliminates the need for an external electronic oscillator and improves magnetometer's stability over temperature. The resonator uses no magnetic materials and is encapsulated using an epitaxial polysilicon layer in a process that is fully compatible with complementary metal-oxide-semiconductor manufacturing. The sensor has a magnetic field resolution of 128 nT/rt-Hz with 2.1 mA bias current. [ABSTRACT FROM AUTHOR]

The global drive for improvements in the efficiency and quality of healthcare has led to the development of frameworks to assist in defining and measuring 'good quality care'. However, such frameworks lack a systematic or meaningful definition of what 'good quality care' means from the patients' perspective. The present research provides an in-depth analysis of patients' experiences in a hospital setting from a quality of care perspective. Forty-five adults (aged 16-70) hospitalised in one of four UK NHS trusts following an unintentional injury were interviewed about their experiences of care. The findings show variability in perceived quality of care within the same hospital episode which cannot be meaningfully captured by existing frameworks. The context of trauma care (e.g. distressing nature of injury, patient vulnerability, expectations of hospitalisation and participants' interaction with different service providers) defined the care experience and the value of being 'cared for'. Participants identified some aspects of good and care which related to holistic, person-centred and personalised care beyond the medical needs. Participants discussed the value of being understood, staff thinking of their needs beyond hospitalisation, staff trying 'their best' despite constrains of current care, having their emotional needs recognised and addressed and staff competence. Patients reported also poor quality of care and 'not being cared for' by specific staff groups which they expected to fulfil this role, rushed and unsympathetic care, lack of recognition for emotional impact of injury mapped onto existing quality frameworks e.g. safety, equity, accessibility and patient-centeredness as well as quality of interaction with providers, empathetic care which extended beyond medical needs, coordination of care, and the positivity of care delivery as important dimensions of quality care with implications for their recovery. The findings have implications for quality frameworks and theoretical definitions of quality of care; they demonstrate the importance of patient experience in addition to clinical effectiveness and safety as an essential dimension of quality care. In terms of practice, the findings support the need to incorporate knowledge and training of injured adults' psychological needs, and the value of interaction with professionals as a patient defined dimension of the quality of care. [ABSTRACT FROM AUTHOR]

Glutamatergic neurotransmission, important for learning and memory, is disrupted in different ways in patients with Alzheimer's disease (AD) and frontotemporal dementia (FTD) tauopathies. We have previously reported that two tau transgenic mouse models, L1 and L66, produce different phenotypes resembling AD and FTD, respectively. The AD-like L1 model expresses the truncated core aggregation domain of the AD paired helical filament (PHF) form of tau (tau296-390) whereas the FTD-like L66 model expresses full-length tau carrying two mutations at P301S/G335D. We have used synaptosomes isolated from these mice to investigate K + -evoked glutamate release and, if abnormal, to determine responsiveness to hydromethylthionine, a tau aggregation inhibitor previously shown to reduce tau pathology in these models. We report that the transgenes in these two mouse lines cause opposite abnormalities in glutamate release. Over-expression of the core tau unit in L1 produces a significant reduction in glutamate release and a loss of Ca 2+ -dependency compared with wild-type control mice. Full-length mutant tau produces an increase in glutamate release that retains normal Ca 2+ -dependency. Chronic pre-treatment with hydromethylthionine normalises both reduced (L1) and excessive glutamate (L66) and restores normal Ca 2+ -dependency in L1 mice. This implies that both patterns of impairment are the result of tau aggregation, but that the direction and Ca 2+ -dependency of the abnormality is determined by expression of the disease-specific transgene. Our results lead to the conclusion that the tauopathies need not be considered a single entity in terms of the downstream effects of pathological aggregation of tau protein. In this case, directionally opposite abnormalities in glutamate release resulting from different types of tau aggregation in the two mouse models can be corrected by hydromethylthionine. This may help to explain the activity of hydromethylthionine on cognitive decline and brain atrophy in both AD and behavioural-variant FTD., Competing Interests: Declaration of Competing Interest The sponsor was involved in the design of the study; in the collection, analysis, and interpretation of the data; and in the writing of the report. The corresponding author had full access to all the data and had final responsibility for the submission of the report for publication. C.R.H. and C.M.W. are officers in TauRx Therapeutics Ltd., an affiliate of WisTa Laboratories Ltd. G.R. has received funding from TauRx Therapeutics Ltd. D.H., C.R.H., C.M.W., and G.R. are named inventors on patents and patent applications owned by WisTa Laboratories Ltd., (Crown Copyright © 2024. Published by Elsevier Inc. All rights reserved.)

Alpha-Synuclein (α-Syn) aggregation is a pathological feature of synucleinopathies, neurodegenerative disorders that include Parkinson's disease (PD). Here, we explored the efficacy of N,N,N',N'-tetraethyl-10H-phenothiazine-3,7-diamine dihydrochloride (LETC), a protein aggregation inhibitor, on α-Syn aggregation. In both cellular models and transgenic mice, α-Syn aggregation was achieved by the overexpression of full-length human α-Syn fused with a signal sequence peptide. α-Syn accumulated in transfected DH60.21 neuroblastoma cells and α-Syn aggregation was inhibited by LETC with an EC 50 of 0.066 ± 0.047 μM. Full-length human α-Syn overexpressing Line 62 (L62) mice accumulated neuronal α-Syn that was associated with a decreased motor performance in the open field and automated home cage. LETC, administered orally for 6 weeks at 10 mg/kg significantly decreased α-Syn-positive neurons in multiple brain regions and this resulted in a rescue of movement deficits in the open field in these mice. LETC however, did not improve activity deficits of L62 mice in the home cage environment. The results suggest that LETC may provide a potential disease modification therapy in synucleinopathies through the inhibition of α-Syn aggregation., Competing Interests: Declaration of competing interest C.R.H., C.M.W. and J.M.D.S. declare that they are officers in TauRx Therapeutics Ltd., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

Aggregation of tau protein is a pathological hallmark of Alzheimer's disease and other neurodegenerative tauopathies. Inhibition of tau aggregation may provide a method for treatment of these disorders. Methods to identify tau aggregation inhibitors (TAIs) in vitro are useful and here we describe assays for TAIs using purified recombinant tau protein fragments in a cell-free immunoassay format and in a stably transfected cell model to create a more physiological environment., (© 2024. The Author(s), under exclusive license to Springer Science+Business Media, LLC, part of Springer Nature.)

Alpha-Synuclein (α-Syn) accumulation is considered a major risk factor for the development of synucleinopathies such as Parkinson's disease (PD) and dementia with Lewy bodies. We have generated mice overexpressing full-length human α-Syn fused to a membrane-targeting signal sequence under the control of the mouse Thy1-promotor. Three separate lines (L56, L58 and L62) with similar gene expression levels, but considerably heightened protein accumulation in L58 and L62, were established. In L62, there was widespread labelling of α-Syn immunoreactivity in brain including spinal cord, basal forebrain, cortex and striatum. Interestingly, there was no detectable α-Syn expression in dopaminergic neurones of the substantia nigra, but strong human α-Syn reactivity in glutamatergic synapses. The human α-Syn accumulated during aging and formed PK-resistant, thioflavin-binding aggregates. Mice displayed early onset bradykinesia and age progressive motor deficits. Functional alterations within the striatum were confirmed: L62 showed normal basal dopamine levels, but impaired dopamine release (upon amphetamine challenge) in the dorsal striatum measured by in vivo brain dialysis at 9 months of age. This impairment was coincident with a reduced response to amphetamine in the activity test. L62 further displayed greater sensitivity to low doses of the dopamine receptor 1 (D1) agonist SKF81297 but reacted normally to the D2 agonist quinpirole in the open field. Since accumulation of α-Syn aggregates in neurones and synapses and alterations in the dopaminergic tone are characteristics of PD, phenotypes reported for L62 present a good opportunity to further our understanding of motor dysfunction in PD and Lewy body dementia., (Copyright © 2017 The Authors. Published by Elsevier B.V. All rights reserved.)

α-Synuclein (α-Syn) aggregation is a pathological feature of synucleinopathies, neurodegenerative disorders that include Parkinson's disease (PD). We have tested whether N,N,N',N' -tetramethyl-10 H -phenothiazine-3,7-diaminium bis(hydromethanesulfonate) (leuco-methylthioninium bis(hydromethanesulfonate); LMTM), a tau aggregation inhibitor, affects α-Syn aggregation in vitro and in vivo . Both cellular and transgenic models in which the expression of full-length human α-Syn (h-α-Syn) fused with a signal sequence peptide to promote α-Syn aggregation were used. Aggregated α-Syn was observed following differentiation of N1E-115 neuroblastoma cells transfected with h-α-Syn. The appearance of aggregated α-Syn was inhibited by LMTM, with an EC 50 of 1.1 μM, with minimal effect on h-α-Syn mRNA levels being observed. Two independent lines of mice (L58 and L62) transgenic for the same fusion protein accumulated neuronal h-α-Syn that, with aging, developed into fibrillary inclusions characterized by both resistance to proteinase K (PK)-cleavage and their ability to bind thiazin red. There was a significant decrease in α-Syn-positive neurons in multiple brain regions following oral treatment of male and female mice with LMTM administered daily for 6 weeks at 5 and 15 mg MT/kg. The early aggregates of α-Syn and the late-stage fibrillar inclusions were both susceptible to inhibition by LMTM, a treatment that also resulted in the rescue of movement and anxiety-related traits in these mice. The results suggest that LMTM may provide a potential disease modification therapy in PD and other synucleinopathies through the inhibition of α-Syn aggregation.

Aggregation of tau protein is a pathological hallmark of Alzheimer's disease and other neurodegenerative tauopathies. Inhibition of tau aggregation could provide a method for the treatment of these disorders. Methods to identify tau aggregation inhibitors (TAIs) in vitro are useful and here we describe assays for TAIs using purified recombinant tau protein fragments in a cell-free immunoassay format and a stably transfected cell model to create a more physiological environment.

Given the repeated failure of amyloid-based approaches in Alzheimer's disease, there is increasing interest in tau-based therapeutics. Although methylthioninium (MT) treatment was found to be beneficial in tau transgenic models, the brain concentrations required to inhibit tau aggregation in vivo are unknown. The comparative efficacy of methylthioninium chloride (MTC) and leucomethylthioninium salts (LMTX; 5-75 mg/kg; oral administration for 3-8 weeks) was assessed in two novel transgenic tau mouse lines. Behavioural (spatial water maze, RotaRod motor performance) and histopathological (tau load per brain region) proxies were applied. Both MTC and LMTX dose-dependently rescued the learning impairment and restored behavioural flexibility in a spatial problem-solving water maze task in Line 1 (minimum effective dose: 35 mg MT/kg for MTC, 9 mg MT/kg for LMTX) and corrected motor learning in Line 66 (effective doses: 4 mg MT/kg). Simultaneously, both drugs reduced the number of tau-reactive neurons, particularly in the hippocampus and entorhinal cortex in Line 1 and in a more widespread manner in Line 66. MT levels in the brain followed a sigmoidal concentration-response relationship over a 10-fold range (0.13-1.38 μmol/l). These data establish that diaminophenothiazine compounds, like MT, can reverse both spatial and motor learning deficits and reduce the underlying tau pathology, and therefore offer the potential for treatment of tauopathies.

Alzheimer disease (AD) is a degenerative tauopathy characterized by aggregation of Tau protein through the repeat domain to form intraneuronal paired helical filaments (PHFs). We report two cell models in which we control the inherent toxicity of the core Tau fragment. These models demonstrate the properties of prion-like recruitment of full-length Tau into an aggregation pathway in which template-directed, endogenous truncation propagates aggregation through the core Tau binding domain. We use these in combination with dissolution of native PHFs to quantify the activity of Tau aggregation inhibitors (TAIs). We report the synthesis of novel stable crystalline leucomethylthioninium salts (LMTX®), which overcome the pharmacokinetic limitations of methylthioninium chloride. LMTX®, as either a dihydromesylate or a dihydrobromide salt, retains TAI activity in vitro and disrupts PHFs isolated from AD brain tissues at 0.16 μM. The Ki value for intracellular TAI activity, which we have been able to determine for the first time, is 0.12 μM. These values are close to the steady state trough brain concentration of methylthioninium ion (0.18 μM) that is required to arrest progression of AD on clinical and imaging end points and the minimum brain concentration (0.13 μM) required to reverse behavioral deficits and pathology in Tau transgenic mice., (© 2015 by The American Society for Biochemistry and Molecular Biology, Inc.)

Methylthioninium (MT) is a tau aggregation inhibitor with therapeutic potential in Alzheimer's disease (AD). MT exists in equilibrium between reduced [leucomethylthioninium (LMT)] and oxidized (MT(+)) forms; as a chloride salt [methylthioninium chloride (MTC), "methylene blue"], it is stabilized in its MT(+) form. Although the results of a phase 2 study of MTC in 321 mild/moderate AD subjects identified a 138-mg MT/day dose as the minimum effective dose on cognitive and imaging end points, further clinical development of MT was delayed pending resolution of the unexpected lack of efficacy of the 228-mg MT/day dose. We hypothesized that the failure of dose response may depend on differences known at the time in dissolution in simulated gastric and intestinal fluids of the 100-mg MTC capsules used to deliver the 228-mg dose and reflect previously unsuspected differences in redox processing of MT at different levels in the gut. The synthesis of a novel chemical entity, LMTX (providing LMT in a stable anhydrous crystalline form), has enabled a systematic comparison of the pharmacokinetic properties of MTC and LMTX in preclinical and clinical studies. The quantity of MT released in water or gastric fluid within 60 minutes proved in retrospect to be an important determinant of clinical efficacy. A further factor was a dose-dependent limitation in the ability to absorb MT in the presence of food when delivered in the MT(+) form as MTC. A model is presented to account for the complexity of MT absorption, which may have relevance for other similar redox molecules., (Copyright © 2014 by The American Society for Pharmacology and Experimental Therapeutics.)

In the Falklands, heavy mortality of rock-hopper penguins Eudyptes chrysocome occurred during the 1985-86 breeding season. Starvation was diagnosed as the primary cause of death, possibly caused by a shortage of euphausiid crustaceans (krill) due to unusual meterological conditions. 'Puffinosis' may possibly have been a contributory factor; otherwise no conclusive evidence of infectious disease or toxicosis was found and also no evidence of radioactive contamination. In the 1986-87 breeding season no unusual mortality occurred, but 99 apparently healthy penguins were examined, i.e., rockhoppers Eudyptes chrysocome syn E. crestatus, gentoos Pygoscelis papua and Magellanics Spheniscus magellanicus. Full necropsies were carried out on 54. Tissue examinations were made for cadmium, copper, iron, manganese, mercury, lead and zinc. High tissue cadmium concentrations found in healthy birds in 1987 were similar to those in penguins which died in 1986, and therefore not considered to be of pathological significance. Although there has been no repetition of the unusually hot 1985-86 breeding season in the Falklands, penguins and other seabirds have had fluctuating breeding successes since then. The precise cause, including the roles of meteorological conditions and overexploitation of some forms of prey species, is unclear.

The HP1 class of chromobox (Cbx) genes encode an evolutionarily conserved family of proteins involved in the packaging of chromosomal domains into a repressive heterochromatic state. The murine Cbx5, Cbx1 and Cbx3 genes encode the three mouse HP1 proteins, mHP1 alpha, -beta and -gamma respectively. Here, we report the cloning of the mouse Cbx3/HP1 gamma gene and the chromosomal localisation of Cbx3 and three Cbx3-related pseudogenes. The Cbx3 structural gene is located on mouse Chromosome 6, close to the Hoxa cluster. Two Cbx3 processed pseudogenes are separated by just 300 bp and are arranged in a head-to-tail configuration on Chromosome 13 while a third pseudogene is found on mouse Chromosome 4. The genomic intron-exon arrangement of Cbx3 is different from the conserved organisation of three other mammalian HP1 genes, Cbx1 (mHP1 beta), CBX3 (hHP1 gamma), and Cbx5 (mHP1 alpha) in that Cbx3 lacks an intron that is present in the others.

Heterochromatin represents a cytologically visible state of heritable gene repression. In the yeast, Schizosaccharomyces pombe, the swi6 gene encodes a heterochromatin protein 1 (HP1)-like chromodomain protein that localizes to heterochromatin domains, including the centromeres, telomeres, and the donor mating-type loci, and is involved in silencing at these loci. We identify here the functional domains of swi6p and demonstrate that the chromodomain from a mammalian HP1-like protein, M31, can functionally replace that of swi6p, showing that chromodomain function is conserved from yeasts to humans. Site-directed mutagenesis, based on a modeled three-dimensional structure of the swi6p chromodomain, shows that the hydrophobic amino acids which lie in the core of the structure are critical for biological function. Gel filtration, gel overlay experiments, and mass spectroscopy show that HP1 proteins can self-associate, and we suggest that it is as oligomers that HP1 proteins are incorporated into heterochromatin complexes that silence gene activity.

HP1-like chromobox genes comprise an evolutionarily conserved family of genes that encode components of centromeric heterochromatin. In order to investigate the role of the murine HP1-like gene, M31, in heterochromatin formation we have isolated its gene and characterised its transcripts and protein products. PCR products that represent M31 transcripts were detected at the one-cell stage and were maternal in origin. Maternal provision of M31 transcripts may reflect a need for M31 in the formation of a functional centromere in order that there is proper segregation of chromosomes during the early cleavage divisions; studies in fission yeast and Drosophila have suggested a crucial role for HP1-like genes in centromere function. There are three protein products encoded by the M31 gene. Surprisingly, the two smaller products are found almost exclusively in the cytoplasm.

In the field significant differences in maximum photosynthetic O 2 -exchange rate (P m ) were found between leaves of Mycelis muralis (L.) Dumort (Asteraceae) collected from woodland and exposed habitats, with the highest values in the exposed sites- However, there were no differences in the P m of leaves collected from plants growing in grikes (fissures in the limestone pavement), of exposed limestone pavement, despite a greater than four-fold difference in the integrated daily irradiance. Leaves of plants from the open pavement had lower photon yields (ø 1 ) and higher dark respiration rates and light compensation points, in comparison to shaded plants. Under controlled environmental conditions the highest P m of leaves from plants subjected to variations in irradiance were found at the intermediate (8-6 mol photon m -2 d -1 growth light level used. At the highest growth irradiance 17.3 mol photon m -2 d -1 used in the laboratory both P m and ø l were reduced, although the latest plant biomass was found at this irradiance. No changes were found in the chlorophyll a:b ratio over the same range of irradiances. Examination of plant populations of M. muralis, collected from open or shaded habitats and exposed to growth irradiances that covered the range over which increases in photosynthesis were, observed in the laboratory (0.86-8.6 mol photon m -2 d -1 ), resulted in changes in leaf structure and pigment composition. The chlorophyll a:b ratio was low and largely independent of irradiance or the origin of the plant population. Differences in total chlorophyll content were small with the lowest values m the Durrow woodland populations at both irradiances. No variations were found in a number of chloroplast thylakoid structural features. In particular, the ratio of oppressed to non-appressed membranes was unchanged by growth at the two irradiances, consistent with an invariant chlorophyll a:b ratio. Based on peaks in the difference spectra the woodland populations had mi enhanced in vivo absorption at λlD= 650 and 706 nm when grown at low irradiance. These peaks were absent from the population collected from the open limestone pavement. The significance of the enhanced absorption at low irradiance and the possibility that these peaks represent long-wavelength forms of chlorophyll a (λlD = 706) and b (λlD = 650) is discussed. A particular feature of plants grown at high irradiance was an enhanced anthocyanin content in comparison to those grown at low irradiance. This was associated with an increase in absorptance. particularly in the green region (λlD = 550 nm) of the visible spectrum. Overall these results suggest that complete acclimation of photosynthesis and an ability to modulate light-harvesting is not a prerequisite, for success in a high light environment.

Haematological values were determined in 50 Rockhopper (Eudyptes crestatus), 19 Gentoo (Pygoscelis papua) and 12 Magellanic (Spheniscus magellanicus) penguins from various sites on the Falkland Islands. Adult Magellanic penguins had significantly lower haemoglobin (Hb) levels, packed cell volumes (PCV) and red cell counts (RBC) than adults of the other two species. Hb, PCV and RBC values were also lower in juvenile birds than in adults and lower in post-moult than in pre-moult adults. Comparison of findings in wild Rockhopper and Gentoo penguins with values obtained from captive birds showed slight but significant differences in Hb and mean cell haemoglobin concentration, and in the relative numbers of heterophils, lymphocytes, monocytes and eosinophils present.

Post moult rockhopper penguins (Eudyptes crestatus) had significantly higher plasma alpha-tocopherol (vitamin E), total lipid and total cholesterol concentrations than their pre-moult counterparts. In the magellanic penguins (Spheniscus magellanicus) there were post moult increases in total lipid, cholesterol and alpha-tocopherol concentrations, but only the increase in alpha-tocopherol was significant. Plasma alpha-tocopherol, total lipid and total cholesterol concentrations in post moult gentoo (Pygoscelis papua) chicks were similar to those in non-moulting adult gentoos. Species differences in the levels of these nutrients in plasma may be due to differences in their dietary habits.