VRAM Flap for Pelvic Floor Reconstruction after Pelvic Exenteration and Abdominoperineal Excision

Due to the still large number of patients diagnosed with pelvic neoplasms (colorectal, gynecological, and urological) in advanced stages right from the initial diagnosis, surgery represents the mainstay of treatment, often implying wide, eventually multi-organ resections in order to achieve negative surgical margins. Perineal wound morbidity, particularly in extralevator abominoperineal excision, leads to complications and local infection rates of up to 40%. Strategies to reduce postoperative wound complications are being pursued to address this issue. The VRAM flap remains the gold standard for autologous reconstruction after pelvic oncological resection; it was initially designed for abdominal wall defects and later expanded for large pelvic tissue defects. The flap's application is based on its physical characteristics, including abundant tissue and a generous skin paddle, which effectively obliterates dead space after exenterations. The generous skin paddle offers good cosmetic and functional outcomes at the recipient site. This article describes the case of a patient histopathologically diagnosed with stage IIIA squamous cell carcinoma of the uterine cervix who received multimodal onco-surgical treatment. The surgical mainstay of this treatment is pelvic exenteration. Pelvic reconstruction after this major surgery was performed using a vertical flap with the rectus abdominis.

Twinning as a risk factor for neonatal acute intestinal diseases: a case-control study

Introduction

Acute intestinal diseases (AID), including necrotizing enterocolitis and spontaneous intestinal perforation, are a group of conditions that typically present in preterm infants, and are associated with an elevated mortality and morbidity rate. The risk factors for these diseases remain largely unknown. The aim of the study is to identify the correlation between twinning and the development of AID.

Methods

A single-center retrospective case-control study was conducted. We recruited all infants with a diagnosis of AID, confirmed by anatomopathology, recovered in NICU between 2010 and 2020. Considering the rarity of the outcome, 4 matched controls for each subject were randomly chosen from the overall population of newborns. Odds Ratio (OR) and 95% Confidence Interval (CI) were calculated using a conditional logistic regression model and a multivariate model by the creation of a Directed Acyclic Graph (www.dagitty.net).

Results

The study population resulted in 65 cases and 260 controls. The two groups present similar median gestational age and mean birthweight in grams. The cases have a higher frequency of neonatal pathology (defined as at least one of patent ductus arteriosus, early or late sepsis, severe respiratory distress) (84.6% vs. 51.9%), medically assisted procreation (33.8% vs. 18.8%) and periventricular leukomalacia (10.8% vs. 2.7%), and a lower frequency of steroids prophylaxis (67.7% vs. 86.9%). About 50% of cases needed surgery. The OR for the direct effect were difference from one using logistic regression booth without and with repeated measures statements: from 1.14 to 4.21 (p = .019) and from 1.16 to 4.29 (p = .016), respectively.

Conclusions

Our study suggests that twinning may be a risk factor for the development of AID. Due to the small number of cases observed, further studies on larger populations are needed.

Optimization of highly inclined illumination for diffraction-limited and super-resolution microscopy

In HILO microscopy, a highly inclined and laminated light sheet is used to illuminate the sample, thus drastically reducing background fluorescence in wide-field microscopy, but maintaining the simplicity of the use of a single objective for both illumination and detection. Although the technique has become widely popular, particularly in single molecule and super-resolution microscopy, a limited understanding of how to finely shape the illumination beam and of how this impacts on the image quality complicates the setting of HILO to fit the experimental needs. In this work, we build up a simple and comprehensive guide to optimize the beam shape and alignment in HILO and to predict its performance in conventional fluorescence and super-resolution microscopy. We model the beam propagation through Gaussian optics and validate the model through far- and near-field experiments, thus characterizing the main geometrical features of the beam. Further, we fully quantify the effects of a progressive reduction of the inclined beam thickness on the image quality of both diffraction-limited and super-resolution images and we show that the most relevant impact is obtained by reducing the beam thickness to sub-cellular dimensions (< 3 µm). Based on this, we present a simple optical solution that exploits a rectangular slit to reduce the inclined beam thickness down to 2.6 µm while keeping a field-of-view dimension suited for cell imaging and allowing an increase in the number of localizations in super-resolution imaging of up to 2.6 folds.

Particle Localization Using Local Gradients and Its Application to Nanometer Stabilization of a Microscope

Particle localization plays a fundamental role in advanced biological techniques such as single-molecule tracking, superresolution microscopy, and manipulation by optical and magnetic tweezers. Such techniques require fast and accurate particle localization algorithms as well as nanometer-scale stability of the microscope. Here, we present a universal method for three-dimensional localization of single labeled and unlabeled particles based on local gradient calculation of particle images. The method outperforms state-of-the-art localization techniques in high-noise conditions, and it is capable of 3D nanometer accuracy localization of nano- and microparticles with sub-millisecond calculation time. By localizing a fixed particle as fiducial mark and running a feedback loop, we demonstrate its applicability for active drift correction in sensitive nanomechanical measurements such as optical trapping and superresolution imaging. A multiplatform open software package comprising a set of tools for local gradient calculation in brightfield, darkfield, and fluorescence microscopy is shared for ready use by the scientific community.

The Challenges of Colorectal Cancer Surgery during the COVID-19 Pandemic in Romania: A Three-Year Retrospective Study

The predictions on the influence of the SARS-CoV-2 pandemic on access to medical services in Romania predicted a 35% drop in oncological hospitalizations in 2020 compared to the previous decade, raising the hypothesis that patients with colorectal cancer can become indirect victims of the ongoing pandemic. Therefore, the aim of the current research was to observe how the COVID-19 pandemic influenced colorectal cancer surgery in Romania, to determine the level of addressability towards specialized care, to compare the cancer staging between the pandemic and pre-pandemic periods, and to observe the risk factors for disease progression. This retrospective study was spread over three years, respectively, from March 2019 to March 2022, and included a total of 198 patients with a history of colorectal cancer surgery. It was decided to perform a parallel comparison of 2019, 2020, and 2021 to observe any significant changes during the pandemic. Our clinic encountered a significant decrease in all interventions during the pandemic; although the number of CRC surgeries remained constant, the cases were more difficult, with significantly more patients presenting in emergency situations, from 31.3% in 2019 to 50.0% in 2020 and 57.1% in 2021. Thus, the number of elective surgeries decreased significantly. The proportion of TNM (tumor-node-metastasis) staging was, however, statistically significant between the pre-pandemic and pandemic period. In 2019, 13.3% of patients had stage IIa, compared with 28.8% in 2020 and 13.1% in 2021. Similarly, the proportion of very advanced colorectal cancer was higher during the pandemic period of 2020 and 2021 (12.0% in 2019 vs. 12.5% in 2020 and 25.0% in 2021), which was represented by a significantly higher proportion of patients with bowel perforation. Patients with an advanced TNM stage had a 6.28-fold increased risk of disease progression, followed by lymphovascular invasion (HR = 5.19). However, the COVID-19 pandemic, represented by admission years 2020 and 2021, did not pose a significant risk for disease progression and mortality. In-hospital mortality during the pandemic also did not change significantly. After the pandemic restrictions have been lifted, it would be advisable to conduct a widespread colorectal cancer screening campaign in order to identify any instances of the disease that went undetected during the SARS-CoV-2 pandemic.

Editorial to the Special Issue "Molecular Motors: From Single Molecules to Cooperative and Regulatory Mechanisms In Vivo"

The Molecular motors or motor proteins are able to generate force and do mechanical work that is used to displace a load or produce relative movements between molecules or macromolecular assembles [...].

High-Speed Optical Traps Address Dynamics of Processive and Non-Processive Molecular Motors

Interactions between biological molecules occur on very different time scales, from the minutes of strong protein-protein bonds, down to below the millisecond duration of rapid biomolecular interactions. Conformational changes occurring on sub-ms time scales and their mechanical force dependence underlie the functioning of enzymes (e.g., motor proteins) that are fundamental for life. However, such rapid interactions are beyond the temporal resolution of most single-molecule methods. We developed ultrafast force-clamp spectroscopy (UFFCS), a single-molecule technique based on laser tweezers that allows us to investigate early and very fast dynamics of a variety of enzymes and their regulation by mechanical load. The technique was developed to investigate the rapid interactions between skeletal muscle myosin and actin, and then applied to the study of different biological systems, from cardiac myosin to processive myosin V, microtubule-binding proteins, transcription factors, and mechanotransducer proteins. Here, we describe two different implementations of UFFCS instrumentation and protocols using either acousto- or electro-optic laser beam deflectors, and their application to the study of processive and non-processive motor proteins.

Characterization of substituted piperazines able to reverse MDR in Escherichia coli strains overexpressing resistance-nodulation-cell division (RND) efflux pumps

BACKGROUND

MDR in bacteria is threatening to public health. Overexpression of efflux pumps is an important cause of MDR. The co-administration of antimicrobial drugs and efflux pump inhibitors (EPIs) is a promising approach to address the problem of MDR.

OBJECTIVES

To identify new putative EPIs and to characterize their mechanisms of action.

METHODS

The effects of four selected piperazine derivatives on resistance-nodulation-cell division (RND) pumps was evaluated in Escherichia coli strains overexpressing or not expressing RND pumps by assays aimed at evaluating antibiotic potentiation, membrane functionality, ethidium bromide accumulation and AcrB expression. The cytotoxicity of selected piperazines towards primary cultures of human dermal fibroblasts was also investigated.

RESULTS

Four molecules enhanced levofloxacin activity against strains overexpressing RND efflux pumps (AcrAB-TolC and AcrEF-TolC), but not against RND pump-deficient strains. They had little effects on membrane potential. Molecule 4 decreased, whereas the other three increased, membrane permeability compared with untreated control cells. The four molecules showed differences in the specificity of interaction with RND efflux pumps, by inactivating the transport of one or more antibiotics, and in the levels of ethidium bromide accumulation and of acrB expression inhibition.

CONCLUSIONS

Piperazine derivatives are good candidates as inhibitors of RND efflux pumps. They decreased the activity of RND pumps by mixed mechanisms of action. Small structural differences among the molecules can be critical in defining their behaviour.

Dissecting Mechanoenzymatic Properties of Processive Myosins with Ultrafast Force-Clamp Spectroscopy

Ultrafast force-clamp spectroscopy (UFFCS) is a single molecule technique based on laser tweezers that allows the investigation of the chemomechanics of both conventional and unconventional myosins under load with unprecedented time resolution. In particular, the possibility to probe myosin motors under constant force right after the actin-myosin bond formation, together with the high rate of the force feedback (200 kHz), has shown UFFCS to be a valuable tool to study the load dependence of fast dynamics such as the myosin working stroke. Moreover, UFFCS enables the study of how processive and non-processive myosin-actin interactions are influenced by the intensity and direction of the applied force. By following this protocol, it will be possible to perform ultrafast force-clamp experiments on processive myosin-5 motors and on a variety of unconventional myosins. By some adjustments, the protocol could also be easily extended to the study of other classes of processive motors such as kinesins and dyneins. The protocol includes all the necessary steps, from the setup of the experimental apparatus to sample preparation, calibration procedures, data acquisition and analysis.

1-benzyl-1,4-diazepane reduces the efflux of resistance-nodulation-cell division pumps in Escherichia coli

Aim: To investigate the action mechanism of 1-benzyl-1,4-diazepane (1-BD) as efflux pump inhibitor (EPI) in Escherichia coli mutants: ΔacrAB or overexpressing AcrAB and AcrEF efflux pumps. Materials & methods: Effect of 1-BD on: antibiotic potentiation, by microdilution method; membrane functionality, by fluorimetric assays; ethidium bromide accumulation, by fluorometric real-time efflux assay; AcrB expression, by quantitative photoactivated localization microscopy. Results: 1-BD decreases the minimal inhibitory concentration of levofloxacin and other antibiotics and increase ethidium bromide accumulation in E. coli overexpressing efflux pumps but not in the ΔacrAB strain. 1-BD increases membranes permeability, without sensibly affecting inner membrane polarity and decreases acrAB transcription. Conclusion: 1-BD acts as an EPI in E. coli with a mixed mechanism, different from that of major reference EPIs.

Probing force in living cells with optical tweezers: from single-molecule mechanics to cell mechanotransduction

The invention of optical tweezers more than three decades ago has opened new avenues in the study of the mechanical properties of biological molecules and cells. Quantitative force measurements still represent a challenging task in living cells due to the complexity of the cellular environment. Here, we review different methodologies to quantitatively measure the mechanical properties of living cells, the strength of adhesion/receptor bonds, and the active force produced during intracellular transport, cell adhesion, and migration. We discuss experimental strategies to attain proper calibration of optical tweezers and molecular resolution in living cells. Finally, we show recent studies on the transduction of mechanical stimuli into biomolecular and genetic signals that play a critical role in cell health and disease.

Single molecule mechanics resolves the earliest events in force generation by cardiac myosin

Key steps of cardiac mechanochemistry, including the force-generating working stroke and the release of phosphate (P_i), occur rapidly after myosin-actin attachment. An ultra-high-speed optical trap enabled direct observation of the timing and amplitude of the working stroke, which can occur within <200 μs of actin binding by β-cardiac myosin. The initial actomyosin state can sustain loads of at least 4.5 pN and proceeds directly to the stroke or detaches before releasing ATP hydrolysis products. The rates of these processes depend on the force. The time between binding and stroke is unaffected by 10 mM P_i which, along with other findings, indicates the stroke precedes phosphate release. After P_i release, P_i can rebind enabling reversal of the working stroke. Detecting these rapid events under physiological loads provides definitive indication of the dynamics by which actomyosin converts biochemical energy into mechanical work.

A protocol for single molecule imaging and tracking of processive myosin motors

Myosin is a large family of actin-based molecular motors, which includes efficient intracellular transporters that move cargoes and material essential for cell's life. Here, we describe protocols for labelling single myosin motors with quantum dots, tracking them in an in vitro reconstituted single-molecule motility assay, acquiring image stacks and analyzing them. We describe the required steps to obtain trajectories of single myosin motors from which fundamental biophysical parameters such as the motor velocity, run length and step size can be derived. We also describe protocols for an ensemble actin gliding assay, which is valuable to test the motor viability and its ensemble properties. The protocols allow probing the effect of changes in nucleotides, ions, and buffer composition on the motor properties and are easily generalizable to track the movements of different motor proteins.

Ultra-fast force-clamp spectroscopy data on the interaction between skeletal muscle myosin and actin

Ultrafast force-clamp spectroscopy is a single molecule technique based on laser tweezers with sub-millisecond and sub-nanometer resolution. The technique has been successfully applied to investigate the rapid conformational changes that occur when a myosin II motor from skeletal muscle interacts with an actin filament. Here, we share data on the kinetics of such interaction and experimental records collected under different forces [1]. The data can be valuable for researchers interested in the mechanosensitive properties of myosin II, both from an experimental and modeling point of view. The data is related to the research article “ultrafast force-clamp spectroscopy of single molecules reveals load dependence of myosin working stroke” [2].

Myosin V fluorescence imaging dataset for single-molecule localization and tracking

Myosin-5B is one of three members of the myosin-5 family of actin-based molecular motors fundamental in recycling endosome trafficking and collective actin network dynamics. Through single-molecule motility assays, we recently demonstrated that myosin-5B can proceed in 36-nm steps along actin filaments as single motor. By analyzing trajectories of single myosin-5B along actin filaments we showed that its velocity is dependent on ATP concentration, while its run length is independent on ATP concentration, as a landmark of processivity.

Here, we share image stacks acquired under total internal reflection fluorescence (TIRF) microscopy and representative trajectories of single myosin-5B molecules labelled with Quantum Dots (QD-myo-5B) moving along actin filaments at different ATP concentrations (0.3–1000 μM). Localization of QD-myo-5B was performed with the PROOF software, which is freely available [1]. The data can be valuable for researchers interested in molecular motors motility, both from an experimental and modeling point of view, as well as to researchers developing single particle tracking algorithms. The data is related to the research article “Dissecting myosin-5B mechanosensitivity and calcium regulation at the single molecule level” Gardini et al., 2015.

PLANT: A Method for Detecting Changes of Slope in Noisy Trajectories

Time traces obtained from a variety of biophysical experiments contain valuable information on underlying processes occurring at the molecular level. Accurate quantification of these data can help explain the details of the complex dynamics of biological systems. Here, we describe PLANT (Piecewise Linear Approximation of Noisy Trajectories), a segmentation algorithm that allows the reconstruction of time-trace data with constant noise as consecutive straight lines, from which changes of slopes and their respective durations can be extracted. We present a general description of the algorithm and perform extensive simulations to characterize its strengths and limitations, providing a rationale for the performance of the algorithm in the different conditions tested. We further apply the algorithm to experimental data obtained from tracking the centroid position of lymphocytes migrating under the effect of a laminar flow and from single myosin molecules interacting with actin in a dual-trap force-clamp configuration.

Data on the target search by a single protein on DNA measured with ultrafast force-clamp spectroscopy

The mechanism by which proteins are able to find small cognate sequences in the range from few to few tens of base pairs amongst the millions of non-specific chromosomal DNA has been puzzling researchers for decades. Single molecule techniques based on fluorescence have been successfully applied to investigate this process but are inherently limited in terms of spatial and temporal resolution. We previously showed that ultrafast force-clamp spectroscopy, a single molecule technique based on laser tweezers, can be applied to the study of protein-DNA interaction attaining sub-millisecond and few base-pair resolution. Here, we share experimental records of interactions between a single lactose repressor protein and DNA collected under different forces using our technique [1]. The data can be valuable for researchers interested in the study of protein-DNA interaction and the mechanism of DNA target search, both from an experimental and modeling point of view. The data is related to the research article "Sliding of a single lac repressor protein along DNA is tuned by DNA sequence and molecular switching" [2].

Dissecting myosin-5B mechanosensitivity and calcium regulation at the single molecule level

Myosin-5B is one of three members of the myosin-5 family of actin-based molecular motors. Despite its fundamental role in recycling endosome trafficking and in collective actin network dynamics, the molecular mechanisms underlying its motility are inherently unknown. Here we combine single-molecule imaging and high-speed laser tweezers to dissect the mechanoenzymatic properties of myosin-5B. We show that a single myosin-5B moves processively in 36-nm steps, stalls at ~2 pN resistive forces, and reverses its directionality at forces >2 pN. Interestingly, myosin-5B mechanosensitivity differs from that of myosin-5A, while it is strikingly similar to kinesin-1. In particular, myosin-5B run length is markedly and asymmetrically sensitive to force, a property that might be central to motor ensemble coordination. Furthermore, we show that Ca2+ does not affect the enzymatic activity of the motor unit, but abolishes myosin-5B processivity through calmodulin dissociation, providing important insights into the regulation of postsynaptic cargoes trafficking in neuronal cells.

Sliding of a single lac repressor protein along DNA is tuned by DNA sequence and molecular switching

In any living cell, genome maintenance is carried out by DNA-binding proteins that recognize specific sequences among a vast amount of DNA. This includes fundamental processes such as DNA replication, DNA repair, and gene expression and regulation. Here, we study the mechanism of DNA target search by a single lac repressor protein (LacI) with ultrafast force-clamp spectroscopy, a sub-millisecond and few base-pair resolution technique based on laser tweezers. We measure 1D-diffusion of proteins on DNA at physiological salt concentrations with 20 bp resolution and find that sliding of LacI along DNA is sequence dependent. We show that only allosterically activated LacI slides along non-specific DNA sequences during target search, whereas the inhibited conformation does not support sliding and weakly interacts with DNA. Moreover, we find that LacI undergoes a load-dependent conformational change when it switches between sliding and strong binding to the target sequence. Our data reveal how DNA sequence and molecular switching regulate LacI target search process and provide a comprehensive model of facilitated diffusion for LacI.

Electro-optic deflectors deliver advantages over acousto-optical deflectors in a high resolution, ultra-fast force-clamp optical trap

We characterized experimental artifacts arising from the non-linear response of acousto-optical deflectors (AODs) in an ultra-fast force-clamp optical trap and have shown that using electro-optical deflectors (EODs) instead eliminates these artifacts. We give an example of the effects of these artifacts in our ultra-fast force clamp studies of the interaction of myosin with actin filaments. The experimental setup, based on the concept of Capitanio et al. [Nat. Methods 9, 1013-1019 (2012)] utilizes a bead-actin-bead dumbbell held in two force-clamped optical traps which apply a load to the dumbbell to move it at a constant velocity. When myosin binds to actin, the filament motion stops quickly as the total force from the optical traps is transferred to the actomyosin attachment. We found that in our setup, AODs were unsuitable for beam steering due to non-linear variations in beam intensity and deflection angle as a function of driving frequency, likely caused by low-amplitude standing acoustic waves in the deflectors. These aberrations caused instability in the force feedback loops leading to artifactual jumps in the trap position. We demonstrate that beam steering with EODs improves the performance of our instrument. Combining the superior beam-steering capability of the EODs, force acquisition via back-focal-plane interferometry, and dual high-speed FPGA-based feedback loops, we apply precise and constant loads to study the dynamics of interactions between actin and myosin. The same concept applies to studies of other biomolecular interactions.

3D tracking of single nanoparticles and quantum dots in living cells by out-of-focus imaging with diffraction pattern recognition

Live cells are three-dimensional environments where biological molecules move to find their targets and accomplish their functions. However, up to now, most single molecule investigations have been limited to bi-dimensional studies owing to the complexity of 3d-tracking techniques. Here, we present a novel method for three-dimensional localization of single nano-emitters based on automatic recognition of out-of-focus diffraction patterns. Our technique can be applied to track the movements of single molecules in living cells using a conventional epifluorescence microscope. We first demonstrate three-dimensional localization of fluorescent nanobeads over 4 microns depth with accuracy below 2 nm in vitro. Remarkably, we also establish three-dimensional tracking of Quantum Dots, overcoming their anisotropic emission, by adopting a ligation strategy that allows rotational freedom of the emitter combined with proper pattern recognition. We localize commercially available Quantum Dots in living cells with accuracy better than 7 nm over 2 microns depth. We validate our technique by tracking the three-dimensional movements of single protein-conjugated Quantum Dots in living cell. Moreover, we find that important localization errors can occur in off-focus imaging when improperly calibrated and we give indications to avoid them. Finally, we share a Matlab script that allows readily application of our technique by other laboratories.

Combining single-molecule manipulation and imaging for the study of protein-DNA interactions

The paper describes the combination of optical tweezers and single molecule fluorescence detection for the study of protein-DNA interaction. The method offers the opportunity of investigating interactions occurring in solution (thus avoiding problems due to closeby surfaces as in other single molecule methods), controlling the DNA extension and tracking interaction dynamics as a function of both mechanical parameters and DNA sequence. The methods for establishing successful optical trapping and nanometer localization of single molecules are illustrated. We illustrate the experimental conditions allowing the study of interaction of lactose repressor (lacI), labeled with Atto532, with a DNA molecule containing specific target sequences (operators) for LacI binding. The method allows the observation of specific interactions at the operators, as well as one-dimensional diffusion of the protein during the process of target search. The method is broadly applicable to the study of protein-DNA interactions but also to molecular motors, where control of the tension applied to the partner track polymer (for example actin or microtubules) is desirable.

Ultrafast force-clamp spectroscopy of single molecules reveals load dependence of myosin working stroke

We describe a dual-trap force-clamp configuration that applies constant loads between a binding protein and an intermittently interacting biological polymer. The method has a measurement delay of only ∼10 μs, allows detection of interactions as brief as ∼100 μs and probes sub-nanometer conformational changes with a time resolution of tens of microseconds. We tested our method on molecular motors and DNA-binding proteins. We could apply constant loads to a single motor domain of myosin before its working stroke was initiated (0.2-1 ms), thus directly measuring its load dependence. We found that, depending on the applied load, myosin weakly interacted (<1 ms) with actin without production of movement, fully developed its working stroke or prematurely detached (<5 ms), thus reducing the working stroke size with load. Our technique extends single-molecule force-clamp spectroscopy and opens new avenues for investigating the effects of forces on biological processes.

An integrated in vitro and in situ study of kinetics of myosin II from frog skeletal muscle

A new efficient protocol for extraction and conservation of myosin II from frog skeletal muscle made it possible to preserve the myosin functionality for a week and apply single molecule techniques to the molecular motor that has been best characterized for its mechanical, structural and energetic parameters in situ.With the in vitro motility assay, we estimated the sliding velocity of actin on frog myosin II (VF) and its modulation by pH, myosin density, temperature (range 4-30◦C) and substrate concentration. VF was 8.88 ± 0.26 μms⁻¹ at 30.6◦C and decreased to 1.60 ± 0.09 μms⁻¹ at 4.5◦C. The in vitro mechanical and kinetic parameters were integrated with the in situ parameters of frog muscle myosin working in arrays in each half-sarcomere. By comparing VF with the shortening velocities determined in intact frog muscle fibres under different loads and their dependence on temperature, we found that VF is 40-50% less than the fibre unloaded shortening velocity (V0) at the same temperature and we determined the load that explains the reduced value of VF. With this integrated approach we could define fundamental kinetic steps of the acto-myosin ATPase cycle in situ and their relation with mechanical steps. In particular we found that at 5◦C the rate of ADP release calculated using the step size estimated from in situ experiments accounts for the rate of detachment of motors during steady shortening under low loads.

New techniques in linear and non-linear laser optics in muscle research

This review proposes a brief summary of two applications of lasers to muscle research. The first application (laser tweezers), is now a well-established technique in the field, adopted by several laboratories in the world and producing a constant stream of original data, fundamental for our improved understanding of muscle contraction at the level of detail that only single molecule measurements can provide. As an example of the power of this technique, here we focus on some recent results, revealing the performance of the working stroke in at least two distinct steps also in skeletal muscle myosin. A second laser-based technique described here is second-harmonic generation; the application of this technique to muscle research is very recent. We describe the main results obtained thus far in this area and the potentially remarkable impact that this technology may have in muscle research.

Two independent mechanical events in the interaction cycle of skeletal muscle myosin with actin

During skeletal muscle contraction, regular arrays of actin and myosin filaments slide past each other driven by the cyclic ATP-dependent interaction of the motor protein myosin II (the cross-bridge) with actin. The rate of the cross-bridge cycle and its load-dependence, defining shortening velocity and energy consumption at the molecular level, vary widely among different isoforms of myosin II. However, the underlying mechanisms remain poorly understood. We have addressed this question by applying a single-molecule approach to rapidly ( approximately 300 mus) and precisely ( approximately 0.1 nm) detect acto-myosin interactions of two myosin isoforms having large differences in shortening velocity. We show that skeletal myosin propels actin filaments, performing its conformational change (working stroke) in two steps. The first step ( approximately 3.4-5.2 nm) occurs immediately after myosin binding and is followed by a smaller step ( approximately 1.0-1.3 nm), which occurs much faster in the fast myosin isoform than in the slow one, independently of ATP concentration. On the other hand, the rate of the second phase of the working stroke, from development of the latter step to dissociation of the acto-myosin complex, is very similar in the two isoforms and depends linearly on ATP concentration. The finding of a second mechanical event in the working stroke of skeletal muscle myosin provides the molecular basis for a simple model of actomyosin interaction. This model can account for the variation, in different fiber types, of the rate of the cross-bridge cycle and provides a common scheme for the chemo-mechanical transduction within the myosin family.

Exploring molecular motors and switches at the single-molecule level

Single-molecule techniques have propelled an impressive number of biophysical studies during the last decade. From relatively simple video-microscopy techniques, to sophisticated manipulation and detection apparata, single-molecule techniques are capable of tracking the movements and the reaction trajectories of single enzymatic units. By observing microspheres attached to biomolecules it is possible to follow the motion of molecular motors, or to detect conformational "switching" induced by regulatory proteins. Micromanipulation tools like optical tweezers have been widely applied to understand the mechanisms of linear molecular motors, and have allowed the measurement of the elementary steps and the forces produced by several motor proteins, including myosin, kinesin, and dynein. New experimental assays based on magnetic or optical "wrenches," which are able to apply and detect torques on rotary motors and biopolymers, are opening new possibilities in this field. Here, established and emerging magneto-optical manipulation and video-tracking techniques are reviewed, in the perspective of single molecular motors and regulatory proteins studies.

High-precision measurements of light-induced torque on absorbing microspheres

Laser beams have been demonstrated to be capable of exerting torque as well as forces on microparticles. Using a custom magneto-optic manipulator, we directly measured the torque exerted by laser light on absorbing microspheres as a result of the transfer of spin angular momentum. A general method for measuring torque has been developed, and the experimental apparatus has shown a sensitivity of approximately 1 pN/nm.

Three-dimensional magneto-optic trap for micro-object manipulation

A magneto-optic trap for micro-objects is described. Magnetic beads were trapped by optical tweezers while being rotated by a new integrated magnetic manipulator. Rotation was achieved with eight electromagnets with tip-pole geometry. The time orbital potential technique was used to achieve rotation of magnetic beads. Trapping in three dimensions and rotation of magnetic beads on three axes are demonstrated with forces up to 230 pN and force momenta of up to 10(-16)N m . A position-detection apparatus based on an interferometric scheme provides nanometer sensitivities in a few milliseconds.

In progressive nephropathies, overload of tubular cells with filtered proteins translates glomerular permeability dysfunction into cellular signals of interstitial inflammation

Progression to end-stage renal failure is the final common pathway of many forms of glomerular disease, independent of the type of initial insult. Progressive glomerulopathies have in common persistently high levels of urinary protein excretion and tubulointerstitial lesions at biopsy. Among the cellular mechanisms that may determine progression regardless of etiology, the traffic of excess proteins filtered from glomerulus in renal tubule may have functional importance by initiating interstitial inflammation in the early phase of parenchymal injury. This study analyzes the time course and sites of protein accumulation and interstitial cellular infiltration in two different models of proteinuric nephropathies. In remnant kidneys after 5/6 renal mass ablation, albumin and IgG accumulation by proximal tubular cells was visualized in the early stage, preceding interstitial infiltration of MHC-II-positive cells and macrophages. By double-staining, infiltrates developed at or near tubules containing intracellular IgG or luminal casts. This relationship persisted thereafter despite more irregular distribution of infiltrate. Similar patterns were found in an immune model (passive Heymann nephritis), indicating that the interstitial inflammatory reaction develops at the sites of protein overload, regardless of the type of glomerular injury. Osteopontin was detectable in cells of proximal tubules congested with protein in both models at sites of interstitial infiltration, and by virtue of its chemoattractive action this is likely mediator of a proximal tubule-dependent inflammatory pathway in response to protein load. Protein overload of tubules is a key candidate process translating glomerular protein leakage into cellular signals of interstitial inflammation. Mechanisms underlying the proinflammatory response of tubular cells to protein challenge in diseased kidney should be explored, as well as ways of limiting protein reabsorption/deposition to prevent consequent inflammation and progressive disease.

Pharmacologic control of angiotensin II ameliorates renal disease while reducing renal TGF-beta in experimental mesangioproliferative glomerulonephritis

We evaluated the effect of blocking angiotensin II (AngII) on the development of proteinuria and glomerular injury in antithymocyte serum (ATS) glomerulonephritis. Disease was induced in Sprague-Dawley rats by a single intravenous injection of rabbit ATS. Three groups of rats were considered: group 1 (n = 13), ATS rats with no therapy; group 2 (n = 13), ATS rats treated with angiotensin-converting enzyme inhibitor (40 mg/L lisinopril in the drinking water); and group 3 (n = 13), ATS rats treated with AngII receptor antagonist (50 mg/L L-158,809 in the drinking water). Treatment started 3 hours after ATS injection and lasted 4 days. An additional group of control rats (group 4, n = 13) received preimmune serum. At day 4, ATS rats developed proteinuria (46+/-5 mg/d v control 12+/-1 mg/d; P < 0.01), which was prevented by both lisinopril and L-158,809 (14+/-0.2 mg/d and 15+/-1.6 mg/d, respectively, P < 0.01 v ATS). Systolic blood pressure was comparable in ATS rats and in controls (119+/-4 mm Hg v 120+/-2 mm Hg). Systolic blood pressure values were significantly decreased after either lisinopril or L-158,809 (104+/-3 mm Hg and 101+/-5 mm Hg, respectively; P < 0.01 v ATS). Serum creatinine levels were similar in all groups. Quantitation of proliferating cells and macrophages by analysis of proliferating cell nuclear antigen-positive and ED1-positive cells/glomerular cross-section showed a marked increase in proliferating cell nuclear antigen-positive cells in glomeruli of ATS rats over controls (12.6+/-0.5 cells/glomerular cross-section v 1.9+/-0.2 cells/glomerular cross-section; P < 0.01), which was significantly (P < 0.01) prevented by both treatments (lisinopril, 5.7+/-1.0 cells/glomerular cross-section; L-158,809, 4.8+/-1.5 cells/glomerular cross-section). The increase in ED1-positive cells (10+/-0.7 cells/glomerular cross-section v controls, 1.8+/-0.2 cells/glomerular cross-section; P < 0.01) was also significantly (P < 0.01) reduced by lisinopril and L-158,809 (4.1+/-0.7 cells/glomerular cross-sections and 2.6+/-0.6 cells/glomerular cross-section, respectively). Blocking of AngII activity prevented almost completely the formation of microaneurysms in ATS rats (percent of glomeruli with microaneurysms: ATS, 11.5%+/-3.5%; ATS + lisinopril, 0.4%+/-0.2%; ATS + L-158,809, 0.8%+/-0.8%; controls, 0%). Because AngII is a potent inducer of renal transforming growth factor-beta (TGF-beta), a cytokine involved in the regulation of cell proliferation, matrix deposition, and monocyte migration (which is overexpressed in the kidney of ATS rats), we then evaluated the effect of AngII inhibitors on renal gene expression of TGF-beta1 and on urinary TGF-beta1. TGF-beta1 mRNA levels in kidneys of ATS rats were 3.6-fold higher than those of controls and were reduced by 46% and 32% after treatment with lisinopril and L-158,809, respectively. Urinary TGF-beta1 excretion increased in ATS (37.3+/-6.0 ng/d v controls, 13.8+/-3.4 ng/d; P< 0.01) but was normalized by lisinopril and L-158,809 (7.6+/-1.9 ng/d and 6.4+/-0.4 ng/d, respectively; P < 0.01). Thus, in ATS, blocking AngII synthesis prevents proteinuria and reduces glomerular cell proliferation and inflammatory cell infiltration, possibly by reducing excessive renal TGF-beta synthesis. These findings may be relevant for future strategies in the treatment of human mesangioproliferative glomerulonephritis.

High mitochondrial sequence diversity in linguistic isolates of the Alps

Segment I of the control region of mtDNA (360 bases) was sequenced in seven samples, each of 10 individuals inhabiting villages in the eastern Italian Alps (South Tyrol and Trentino). Three linguistic groups, German, Italian, and Ladin, were represented by two samples each; the seventh sample comes from an isolated group of German origin, the Mocheni, who are linguistically distinct and geographically separated from the bulk of the German speakers. Seventy-four polymorphic sites were identified, defining 63 different haplotypes. Mocheni and Ladin speakers tend to form two clusters in the evolutionary trees inferred from sequences. Analysis of molecular variance shows significant differentiation within samples, among them, and among linguistic groups. Genetic differences between the Ladins and the other groups are not much smaller than between Europeans and some Africans; variation is large within groups, as well, with the exception of only the Mocheni. In the evolutionary trees where the four alpine groups are compared with other European populations, Mocheni and especially Ladins appear as clear outliers. Romansch-speaking Swiss, who are linguistically related to Ladins, are not genetically similar to them, for this segment of DNA. Because the time elapsed since colonization of the Alps (< or = 12,000 years) is short in mutational terms, the only model accounting for the observed relationships between mtDNA variation and linguistic identity seems one in which a population ancestral to Ladin speakers was already differentiated long before the Alps were settled and the current linguistic affiliations were established. For the Mocheni, the results are consistent with a simpler episode of allele loss, from an original genetic pool common to the ancestors of the current German speakers.

Survival of an infant with pulmonary hypoplasia treated with dexamethasone

Pulmonary hypoplasia is lethal in its most severe form; in less severe cases the clinical course is protracted, usually resulting in chronic lung disease. A case of unexpected survival of an infant with clinical and radiologic evidence of pulmonary hypoplasia, in whom dexamethasone was administered, is presented. Possible mechanisms of dexamethasone's influence on outcome are discussed.