Francoise Marga - Academia.edu (original) (raw)

Papers by Francoise Marga

Canadian Journal of Botany, 1990

Biomaterials, Sep 1, 2009

Current limitations of exogenous scaffolds or extracellular matrix based materials have underline... more Current limitations of exogenous scaffolds or extracellular matrix based materials have underlined the need for alternative tissue-engineering solutions. Scaffolds may elicit adverse host responses and interfere with direct cell-cell interaction, as well as assembly and alignment of cell-produced ECM. Thus, fabrication techniques for production of scaffold-free engineered tissue constructs have recently emerged. Here we report on a fully biological self-assembly approach, which we implement through a rapid prototyping bioprinting method for scaffold-free small diameter vascular reconstruction. Various vascular cell types, including smooth muscle cells and fibroblasts, were aggregated into discrete units, either multicellular spheroids or cylinders of controllable diameter (300 to 500 μm). These were printed layer-by-layer concomitantly with agarose rods, used here as a molding template. The post-printing fusion of the discrete units resulted in single-and double-layered small diameter vascular tubes (OD ranging from 0.9 to 2.5 mm). A unique aspect of the method is the ability to engineer vessels of distinct shapes and hierarchical trees that combine tubes of distinct diameters. The technique is quick and easily scalable.

Background: Autologous nerve is the gold standard for bridging gaps in nerve repair, but has seve... more Background: Autologous nerve is the gold standard for bridging gaps in nerve repair, but has several drawbacks including the limited number of donor nerves and harvest site morbidity. Synthetic or autologous guidance tubes have failed to reach autograft quality regeneration except for sensory nerves with small gaps (<3cm). Synthetic and autologous tubes' failure has been linked to low density of supporting cells, such as Schwann cells (SC), and the lack of longitudinally-oriented structural features. As a result, tissue engineering has emerged as a promising alternative. Method: A bioengineered nerve conduit was created using a novel tissue engineering technology, namely bioprinting. Constructs were composed of SC and bone marrow stem cells (BMSC) were added for their adherence qualities and implications in chronic pain treatment. No scaffold was used. Cylindrical bio-ink units are stacked according to a computer script. The construct matures for 10 days post-printing to allo...

Essentials of 3D Biofabrication and Translation, 2015

Replacement of the natural promoter of the b-mannanase gene ofStreptomyces lividansbylacpresulted... more Replacement of the natural promoter of the b-mannanase gene ofStreptomyces lividansbylacpresulted in a 15-fold increase in enzyme production over that of the previously reported clone S. lividans IAF36, a clone carrying multiple copies ofmanA, and a 350-fold increase over that of the wild-type strainS. lividans1326. In addition, the use oflacpin the shuttle vector pIAF199 allowed synthesis of the enzymes on

PLANT PHYSIOLOGY, 2004

To test the role of cortical microtubules in aligning cellulose microfibrils and controlling anis... more To test the role of cortical microtubules in aligning cellulose microfibrils and controlling anisotropic expansion, we exposed Arabidopsis thaliana roots to moderate levels of the microtubule inhibitor, oryzalin. After 2 d of treatment, roots grow at approximately steady state. At that time, the spatial profiles of relative expansion rate in length and diameter were quantified, and roots were cryofixed, freeze-substituted, embedded in plastic, and sectioned. The angular distribution of microtubules as a function of distance from the tip was quantified from antitubulin immunofluorescence images. In alternate sections, the overall amount of alignment among microfibrils and their mean orientation as a function of position was quantified with polarized-light microscopy. The spatial profiles of relative expansion show that the drug affects relative elongation and tangential expansion rates independently. The microtubule distributions averaged to transverse in the growth zone for all treatments, but on oryzalin the distributions became broad, indicating poorly organized arrays. At a subcellular scale, cellulose microfibrils in oryzalin-treated roots were as well aligned as in controls; however, the mean alignment direction, while consistently transverse in the controls, was increasingly variable with oryzalin concentration, meaning that microfibril orientation in one location tended to differ from that of a neighboring location. This conclusion was confirmed by direct observations of microfibrils with field-emission scanning electron microscopy. Taken together, these results suggest that cortical microtubules ensure microfibrils are aligned consistently across the organ, thereby endowing the organ with a uniform mechanical structure. ; fax 413-545-3243.

Microscopy and Microanalysis, 2005

ABSTRACT Extended abstract of a paper presented at Microscopy and Microanalysis 2005 in Honolulu,... more ABSTRACT Extended abstract of a paper presented at Microscopy and Microanalysis 2005 in Honolulu, Hawaii, USA, July 31--August 4, 2005.

$Research paper thumbnail of Agar fractions could protect apple shoots cultured in liquid media against hyperhydricity$

Plant Cell Tissue and Organ Culture, 1997

Apple shoots were grown in a Murashige and Skoog liquid proliferation medium containing 4.4 10 -6... more Apple shoots were grown in a Murashige and Skoog liquid proliferation medium containing 4.4 10 -6 M BA, and supplemented with various fractions of agar. Hydrolysed agar from Difco was able to overcome hyperhydricity when its concentration was increased to 0.7%. Among the fractions isolated from this hydrolysed agar, only oligosaccharides were found to reduce the occurrence of this developmental

The notion of tissue surface tension has provided a physical understanding of morphogenetic pheno... more The notion of tissue surface tension has provided a physical understanding of morphogenetic phenomena such as tissue spreading or cell sorting. The measurement of tissue surface tension so far relied on strong approximations on the geometric profile of a spherical droplet compressed between parallel plates. We solved the Laplace equation for this geometry and tested its solution on true liquids and embryonic tissue fragments as well as multicellular aggregates. The analytic solution provides the surface tension in terms of easily and accurately measurable geometric parameters. Experimental results show that the various tissues and multicellular aggregates studied here are incompressible and, similarly to true liquids, possess effective surface tensions that are independent of the magnitude of the compressive force and the volume of the droplet.

The Plant journal : for cell and molecular biology, 2005

Enlargement of the cell wall requires separation of cellulose microfibrils, mediated by proteins ... more Enlargement of the cell wall requires separation of cellulose microfibrils, mediated by proteins such as expansin; according to the multi-net growth hypothesis, enlargement passively reorients microfibrils. However, at the molecular scale, little is known about the specific movement of microfibrils. To find out, we examined directly changes in microfibril orientation when walls were extended slowly in vitro under constant load (creep). Frozen-thawed cucumber hypocotyl segments were strained by 20-30% by incubation in pH 4.5 buffer or by incubation of heat-inactivated segments in a-expansin or a fungal endoglucanase (Cel12A). Subsequently, the innermost layer of the cell wall was imaged, with neither extraction nor homogenization, by field-emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). AFM images revealed that sample preparation for FESEM did not appreciably alter cell wall ultrastructure. In both FESEM and AFM, images from extended and non-extended samples appeared indistinguishable. To quantify orientational order, we used a novel algorithm to characterize the fast Fourier transform of the image as a function of spatial frequency. For both FESEM and AFM images, the transforms of non-extended samples were indistinguishable from those of samples extended by a-expansin or Cel12A, as were AFM images of samples extended by acidic buffer. We conclude that cell walls in vitro can extend slowly by a creep mechanism without passive reorientation of innermost microfibrils, implying that wall loosening agents act selectively on the cross-linking polymers between parallel microfibrils, rather than more generally on the wall matrix.

Biophysical Journal, 2010

heparin. A set of methods was applied: Surface Plasmon Resonance (SPR) was chosen to continuously... more heparin. A set of methods was applied: Surface Plasmon Resonance (SPR) was chosen to continuously monitor the self-assembly process of physi-sorption of subsequent PE layers and to report about deposition efficiency, dynamics and stability of the PEM film. Atomic force microscopy (AFM) was used to visualize and characterize the surface topology obtained after subsequent steps of the layer-by-layer deposition. The multi-layer structure of the composite film and its hydration were studied with neutron reflectometry. The knowledge gathered so far on this system is now being applied for the deposition of lipid bilayers and other biomimetic systems for subsequent biophysical studies.

Biophysical Journal, 2009

Current topics in developmental biology, 2008

A distinguishing feature of a multicellular living system is that it operates at various scales, ... more A distinguishing feature of a multicellular living system is that it operates at various scales, from the intracellular to organismal. Genes and molecules set up the conditions for the physical processes to act, in particular to shape the embryo. As development continues the changes brought about by the physical processes lead to changes in gene expression. It is this coordinated interplay between genetic and generic (i.e. physical and chemical) processes that constitutes the modern understanding of early morphogenesis. It is natural to assume that in this multi-scale process the smaller defines the larger. In case of biophysical properties, in particular, those at the subcellular level are expected to give rise to those at the tissue level and beyond. Indeed, the physical properties of tissues vary greatly from the liquid to solid. Very little is known at present on how tissue level properties are related to cell and subcellular properties. Modern measurement techniques provide quantitative results at both the intracellular and tissue level, but not on the connection between these. In the present work we outline a framework to address this connection. We specifically concentrate on the morphogenetic process of tissue fusion, by following the coalescence of two contiguous multicellular aggregates. The time evolution of this process can accurately be described by the theory of viscous liquids. We also study fusion by Monte Carlo simulations and a novel Cellular Particle Dynamics (CPD) model, which is similar to the earlier introduced Subcellular Element Model (SEM; ). Using the combination of experiments, theory and modeling we are able to relate the measured tissue level biophysical quantities to subcellular parameters. Our approach has validity beyond the particular morphogenetic process considered here and provides a general way to relate biophysical properties across scales.

Introduction: Ovarian Carcinoma MetastasisTumors arising from the ovarian surface epithelium (OSE... more Introduction: Ovarian Carcinoma MetastasisTumors arising from the ovarian surface epithelium (OSE) account for the vast majority of ovarian malignancies; however, the etiology of epithelial ovarian cancer (EOC) remains poorly understood,1 and the analysis of early events in ovarian carcinogenesis is limited by the relative lack of early-stage tumors for study. The normal OSE is a single layer of mesodermally derived cells that exhibit the remarkable ability to transition between epithelial and fibroblastic phenotypes in response to microenvironmental cues.2–4 Such phenotypic plasticity is usually limited to immature, regenerating, or neoplastic epithelium. Unlike most carcinomas that initially de-differentiate during neoplastic progression, ovarian carcinomas undergo a mesenchymal-epithelial transition and acquire a more differentiated epithelial phenotype resulting in significant morphologic heterogeneity as tumors acquire increasingly complex differentiation reminiscent of the highly ...