Characterization of a synthetic bacterial self-destruction device for programmed cell death and for recombinant proteins release

<p>Abstract</p> <p>Background</p> <p>Bacterial cell lysis is a widely studied mechanism that can be achieved through the intracellular expression of phage native lytic proteins. This mechanism can be exploited for programmed cell death and for gentle cell disruption to release recombinant proteins when <it>in vivo </it>secretion is not feasible. Several genetic parts for cell lysis have been developed and their quantitative characterization is an essential step to enable the engineering of synthetic lytic systems with predictable behavior.</p> <p>Results</p> <p>Here, a BioBrick™ lysis device present in the Registry of Standard Biological Parts has been quantitatively characterized. Its activity has been measured in <it>E. coli </it>by assembling the device under the control of a well characterized N-3-oxohexanoyl-L-homoserine lactone (HSL) -inducible promoter and the transfer function, lysis dynamics, protein release capability and genotypic and phenotypic stability of the device have been evaluated. Finally, its modularity was tested by assembling the device to a different inducible promoter, which can be triggered by heat induction.</p> <p>Conclusions</p> <p>The studied device is suitable for recombinant protein release as 96% of the total amount of the intracellular proteins was successfully released into the medium. Furthermore, it has been shown that the device can be assembled to different input devices to trigger cell lysis in response to a user-defined signal. For this reason, this lysis device can be a useful tool for the rational design and construction of complex synthetic biological systems composed by biological parts with known and well characterized function. Conversely, the onset of mutants makes this device unsuitable for the programmed cell death of a bacterial population.</p

A standard vector for the chromosomal integration and characterization of BioBrick™ parts in Escherichia coli

BACKGROUND: The chromosomal integration of biological parts in the host genome enables the engineering of plasmid-free stable strains with single-copy insertions of the desired gene networks. Although different integrative vectors were proposed, no standard pre-assembled genetic tool is available to carry out this task. Synthetic biology concepts can contribute to the development of standardized and user friendly solutions to easily produce engineered strains and to rapidly characterize the desired genetic parts in single-copy context. RESULTS: In this work we report the design of a novel integrative vector that allows the genomic integration of biological parts compatible with the RFC10, RFC23 and RFC12 BioBrick™ standards in Escherichia coli. It can also be specialized by using BioBrick™ parts to target the desired integration site in the host genome. The usefulness of this vector has been demonstrated by integrating a set of BioBrick™ devices in two different loci of the E. coli chromosome and by characterizing their activity in single-copy. Construct stability has also been evaluated and compared with plasmid-borne solutions. CONCLUSIONS: Physical modularity of biological parts has been successfully applied to construct a ready-to-engineer BioBrick™ vector, suitable for a stable chromosomal insertion of standard parts via the desired recombination method, i.e. the bacteriophage integration mechanism or homologous recombination. In contrast with previously proposed solutions, it is a pre-assembled vector containing properly-placed restriction sites for the direct transfer of various formats of BioBrick™ parts. This vector can facilitate the characterization of parts avoiding copy number artefacts and the construction of antibiotic resistance-free engineered microbes, suitable for industrial use

Safe use of human anatomical preparations in frontal and interactive teaching

In the institute of Human Anatomy of Pavia, the use of cadaver dissection is not economically feasible. In order to improve students’ preparation related to topography of the central nervous system, we decided to use formalin-fixed brains and cranial sections belonging to the collection of cadaveric specimens. These specimens, preserved in formalin, however cannot be manipulated as such by the students because formalin can cause headaches, burning sensation in the throat, difficult breathing and can trigger or aggravate asthma symptoms [1, 2]. Furthermore, formalin is known to be a human carcinogen [3]. In order to minimize toxic effects, whole brains were extensively washed in running water and then sliced according to different reference planes using a “home-made” device enabling cuts according to parallel planes. Finally, the resulting sections were inserted into transparent plastic envelopes, immerged in a solution composed by 0.5% agar and 1% sodium azide as preservative. Medical students can now use these human brain sections to test their own ability to recognize nervous system structures. This strategy optimize specimen’s choice and focalize student’s attention on peculiar, selected human samples in full compliance with current security laws

Low-Power Ultrasounds as a Tool to Culture Human Osteoblasts inside Cancellous Hydroxyapatite

Bone graft substitutes and cancellous biomaterials have been widely used to heal critical-size long bone defects due to trauma, tumor resection, and tissue degeneration. In particular, porous hydroxyapatite is widely used in reconstructive bone surgery owing to its biocompatibility. In addition, the in vitro modification of cancellous hydroxyapatite with osteogenic signals enhances the tissue regeneration in vivo, suggesting that the biomaterial modification could play an important role in tissue engineering. In this study, we have followed a tissue-engineering strategy where ultrasonically stimulated SAOS-2 human osteoblasts proliferated and built their extracellular matrix inside a porous hydroxyapatite scaffold. The ultrasonic stimulus had the following parameters: average power equal to 149 mW and frequency of 1.5 MHz. In comparison with control conditions, the ultrasonic stimulus increased the cell proliferation and the surface coating with bone proteins (decorin, osteocalcin, osteopontin, type-I collagen, and type-III collagen). The mechanical stimulus aimed at obtaining a better modification of the biomaterial internal surface in terms of cell colonization and coating with bone matrix. The modified biomaterial could be used, in clinical applications, as an implant for bone repair

Muscle hypertrophy and vascularization induction using human recombinant proteins

Met-Activating Genetically Improved Chimeric Factor-1 (Magic-F1) is an engineered protein that contains two human Met-binding domains. Previous experiments in both homozygous and hemizygous transgenic mice demonstrated that the skeletal muscle specific expression of Magic-F1 can induce a constitutive muscular hypertrophy, increasing the vessel number in fast twitch fibers, also improving running performance and accelerating muscle regeneration after injury [1]. We also found that Magic-F1 could be responsible of muscular hypertrophy inteacting with Pax3 signal pathway in skeletal muscle precursor cells [2]. In order to evaluate the therapeutic potential of Magic-F1, we tested its effect on multipotent and pluripotent stem cells [3]. Murine mesoangioblasts (adult vessel-associated stem cells) expressing Magic-F1 were able to differentiate spontaneously forming myotubes. In addition, in Magic-F1 inducible murine embryonic stem cells subjected to myogenic differentiation, the presence of recombinant protein resulted in improved myogenic commitment. Finally, the microarray analysis of Magic-F1+/+ satellite cells evidenced transcriptomic changes in genes involved in the control of muscle growth, development and vascularisation [4]. Taken together our results candidate Magic-F1 as a potent myogenic inducer, able to affect positively the vascular network, increasing vessel number in fast twitch fibers and modulating the gene expression profile in myogenic progenitors

Stretching optimization for lower limb posterior chain: comparison between two different executions of the same exercise

Stretching of the posterior kinetic chain muscles, especially the hamstrings, is one of the most practiced exercises in all types of physical activity and postural rehabilitation protocols (1). Objective of our experimental trial was to compare the performance of two different variants of muscle stretching (A and B), highlighting for each one the regions of the posterior kinetic chain (lumbar region, gluteus muscles, hamstrings) most affected by the exercise. 161 selected subjects reported on a specific Body Chart the localization of the stretching sensation; the software Pain-drawing (2) was employed for the analysis of the stretching sensation felt by each subject (75 men and 86 women) aged between 20 and 80 years old, with different lifestyles but subjected to defined exclusion criteria (prosthesis, artificial implants, crippling arthritis, flare–up pain, recent surgical procedures). Stretching A is the generally accepted practice available in the literature. The proposed variant (Stretching B) is the experimental suggested procedure which adapts the execution of the exercise on biomechanical reasoning, in order to focus the stretching sensation on the hamstrings muscles and, at the same time, decreasing the stress in the lumbar region. In stretching B, subjects were positioned with lower limb in neutral position, knee with approximately 18° of feeble bending (variable depth, compact rolls in various size, behind popliteal fossa. Notably, results show that the same area has not been affected; when subjects performed Stretching B exercise avoids both the pre-tension of the hamstrings and the lever created by the arms stretched forward, focusing the stretching sensation on the hamstrings muscles and gastrocnemius and affecting only marginally the lumbar region and never the back region. This appears particularly relevant for the prevention of lower back pain and for situation when the stretching of the posterior kinetic chain is performed as a cool-down following physical activity or for rehabilitation purposes

Teaching and learning human Anatomy in the University of Pavia: from models and clinical specimens to prosection on 3D models from our museum collection

Due to decline of resources and support for teaching human anatomy, in our Institute the use of cadaver dissection is not economically feasible. After a few years in which I was able to perform prosection on fixed organs belonging to the Institute collection, over the last years students learned topographical anatomy on commercial plastic models (bones, muscles, joints, trunks and brains). New perspectives recently occurred thanks to a collaboration with Prof. Auricchio’s group, which is involved in the strategic plan “3DPRINTING” (http://www. unipv.eu/site/home/area-stampa/articolo12952.html). First, we have segmented DICOM images of Computed Tomography (CT) to reconstruct 3D models of all the feet’s bones from a patient. Then, these 3D models have been post-processed to obtain suitable file for 3D printing. A 3DSYSTEMS ProJet 460 Plus, professional, full-color binder jetting printer (property of General Surgery2), has been used to create 3D models of feet’s bone by chalk powder binding. Medical students will use these models to test their own ability to recognize feet’s bones shape and to recompose them. Second, a plastic 3D anatomical model has been scanned by Artec Eva 3D Object Scanner to obtain a 3D virtual model of the physical one; this model has been modified to create a new modular model, printed with a process similar to one described above. Our Anatomy Institute is enriched by a Museum, established in the late eighteenth century by universally known anatomists (Rezia, Scarpa, Panizza, Zoja). This historical collection contains several sections (osteology, angiology, splanchnology, neurology and topographic anatomy). It is impossible to use these anatomical specimens of historical interest for prosection, but their life-size copies will constitute a cheap and effective method of learning. This strategy could not replace cadaver dissection experience but we hope that it could assist students in the comprehension of anatomical systems in a cost effective way within a systemic anatomy course. Besides, this method should optimize specimen’s choice and focalize student’s attention on peculiar, selected samples, preparing more appropriately medical students to their clinical practice