Using reverse engineering and computational fluid dynamics to investigate a lower arm amputee swimmer's performance

In front crawl swimming, the hand and the corresponding forearm generate major propulsive forces. Such forces have been studied largely through experimental tests and more recently through the use of steady computational fluid dynamics (CFD). However, the effect of the upper arm on the propulsive forces has generally not been taken into consideration. An understanding of such forces is fundamental for the performance of swimmers who have an arm amputation at the level of the elbow. This study introduces the great potential offered by the multidisciplinary approach combining reverse engineering and unsteady CFD in a novel dynamic and interactive way. A complex CFD mesh model, representing the swimmer body and its upper arm, is produced. The model, including the arm rotation and a body roll movement, interacts dynamically with the fluid flow. Forces generated by the upper arm can then be investigated in great detail. In this particular study, it is found that the upper arm effectively contributes to the propulsion of the body. The propulsive force was numerically computed throughout the pull and reaches maxima of 8N. Results obtained in this study could be extended in a similar way to any other limb movement within a fluid flow.     

Sex ratio and sexual dimorphism in mountain dioecious thuriferous juniper (Juniperus thurifera L., Cupressaceae)

Thuriferous juniper ( Juniperus thurifera L), a dioecious bush or tree is only found in isolated parts of the western Mediterranean: France, Spain, Algeria and Morocco. These mountain juniper stands are seriously endangered in Morocco as a result of intensive wood removal, and in Europe as a result of recolonization of stands by pines or oaks. Field studies were conducted to investigate sex ratio and sexual dimorphism, never previously examined, in eight different populations in the Atlas mountains and, for comparison, in one of two populations in the French Pyrenees. The sex ratio was female-biased for six of the eight Moroccan stands and especially for the oldest populations. The Pyrenean population showed a similar female-biased ratio. This particular sex ratio is possibly linked to cost of reproduction, paid by both males and females. Sex ratios can also be linked to population dynamics. Males begin to flower slightly younger than females, which explains their apparent dominance in young populations in Morocco or in a recolonization zone with young trees in the Pyrenees. Studies concerning sexual dimorphism in the western High Atlas sites showed no significant difference in phytomass between males and females. Females appear to be significantly taller but with a lower radial growth. © 2002 The Linnean Society of London, Botanical Journal of the Linnean Society , 138 , 237–244.     

Seasonal morphophysiological variations in the prostatic complex of the Tarabul’s gerbil (Gerbillus tarabuli)

Gerbillus tarabuli is a nocturnal Saharan rodent which has an annual reproductive cycle characterized by the reproductive activity in spring and a long phase of sexual quiescence in other seasons. We describe the morphology and hormonal regulation of the prostatic complex of this rodent in the two periods, based on anatomical, histological, morphometric, and immunohistochemical analyses. The organisation of this prostatic complex is similar to that reported for Meriones unguiculatus, but different from the prostate of Psammomys obesus, the rat, and the mouse. In addition to the anterior lobes, ventral lobes, and dorsal lobes, the prostatic complex of Gerbillus tarabuli, also includes dorsolateral lobe. Each lobe is composed of a fibro-muscular stroma surrounding a glandular epithelium. Dorsolateral lobes are easily distinguishable by their big volume. The prostate grows and regresses cyclically throughout the year. During the resting season, ventral lobes and anterior lobes showed atrophy, with a significant decrease in both epithelial height and supranuclear area size, and a strong thickening of the fibro-muscular compartment. In dorsal lobes, the epithelial and stromal compartments atrophied and regenerated simultaneously, whereas in dorsolateral lobe the thickness of the epithelium, the supranuclear zone and the stroma increased during resting period. Furthermore, seasonal variations were observed in the distribution and expression of both androgen receptors, and estrogens receptors. Expression patterns of all receptors were lobe-specific. In conclusion, both androgens and estrogens are involved in the homeostasis and regulation of the prostate in Gerbillus tarabuli. Dorsolateral lobe seems to be controlled by a different mechanism than other lobes.     

Matching Patterns of Gene Expression to Mechanical Stiffness at Cell Resolution through Quantitative Tandem Epifluorescence and Nanoindentation

Cell differentiation has been associated with changes in mechanical stiffness in single-cell systems, yet it is unknown whether this association remains true in a multicellular context, particularly in developing tissues. In order to address such questions, we have developed a methodology, termed quantitative tandem epifluorescence and nanoindentation, wherein we sequentially determine cellular genetic identity with confocal microscopy and mechanical properties with atomic force microscopy. We have applied this approach to examine cellular stiffness at the shoot apices of Arabidopsis (Arabidopsis thaliana) plants carrying a fluorescent reporter for the CLAVATA3 (CLV3) gene, which encodes a secreted glycopeptide involved in the regulation of the centrally located stem cell zone in inflorescence and floral meristems. We found that these CLV3-expressing cells are characterized by an enhanced stiffness. Additionally, by tracking cells in young flowers before and after the onset of GREEN FLUORESCENT PROTEIN expression, we observed that an increase in stiffness coincides with this onset. This work illustrates how quantitative tandem epifluorescence and nanoindentation can reveal the spatial and temporal dynamics of both gene expression and cell mechanics at the shoot apex and, by extension, in the epidermis of any thick tissue.Morphogenesis is a complex process that results from the coordinated actions of many genes and gene products across developing tissues and organs. Because shape is a function of the structural elements of cells, the molecular and genetic control of growth and morphogenesis must rely on the regulation of the mechanics of these elements. In this context, cell differentiation has been linked with mechanical stiffness in animal single-cell systems (Collinsworth et al., 2002; Balland et al., 2006; Engler et al., 2006; Darling et al., 2008), although the direct measurement of cell mechanics in growing animal tissues remains elusive (Blanchard and Adams, 2011; Davidson, 2011).In plants, growth involves a delicate mechanical balance: it is powered by turgor pressure and contained by cell wall stiffness (Cosgrove, 1986). Several groups have recently achieved mechanical measurements made at a subcellular resolution in plants (Milani et al., 2011; Peaucelle et al., 2011; Fernandes et al., 2012; Radotić et al., 2012; Routier-Kierzkowska et al., 2012) using scaled-down indentation methods (Geitmann, 2006; Hayot et al., 2012; Milani et al., 2013; Routier-Kierzkowska and Smith, 2013), wherein one quantifies the force needed to push down on a sample to a prescribed depth. These studies have revealed spatiotemporal patterns of stiffness, notably in tissues (Milani et al., 2011; Peaucelle et al., 2011; Fernandes et al., 2012; Routier-Kierzkowska et al., 2012).However, these measurements have not been associated directly with cell identity. This association would become feasible if mechanical measurements were combined with optical imaging of fluorescent reporters. Such a combination, termed nanoindentation coupled to inverted optical microscopy, has already been developed for single animal cells and for thin plant tissues, (Rotsch and Radmacher, 2000; Routier-Kierzkowska and Smith, 2014), but it cannot be extended to thick tissues because they are opaque, making it impossible to simultaneously observe the tissue surface optically with an inverted microscope and probe it mechanically. To circumvent this difficulty, we have developed a methodology involving the use of three microscopes to image the same sample: (1) an atomic force microscope (AFM), which is a nanoindentation system for obtaining stiffness maps of the surface of a sample; (2) an AFM-coupled upright epifluorescence macroscope to precisely identify the points to be probed; and (3) a confocal microscope to determine cell fate at cellular resolution, which may in turn be correlated with the stiffness maps. We call this methodology quantitative tandem epifluorescence and nanoindentation (qTEN), and we use it to probe the shoot apical meristem (SAM) of Arabidopsis (Arabidopsis thaliana), which is a good model system in which to investigate morphogenesis.The SAM is located at the growing tip of the shoot and consists of distinct functional zones (Ha et al., 2010). One of these zones is the slow-dividing central zone (CZ), which can be defined by the expression of the CLAVATA3 (CLV3) signaling glycopeptide. Through cell division, cells exit the CZ into the surrounding peripheral zone (PZ). In the PZ, cells proliferate rapidly, and some become incorporated into organ primordia, thus yielding all aerial organs of the plant. Recent work on the SAM has revealed patterns of mechanical properties (Milani et al., 2011; Peaucelle et al., 2011; Kierzkowski et al., 2012; Braybrook and Peaucelle, 2013), but it is still unclear how these patterns are related to the activity of the SAM or to its functional zonation. Here, we analyze the dynamics of such a mechanical pattern in vivo and show that it is spatially and temporally related to stem cell fate.     

A Comparative Mechanical Analysis of Plant and Animal Cells Reveals Convergence across Kingdoms

Plant and animals have evolved different strategies for their development. Whether this is linked to major differences in their cell mechanics remains unclear, mainly because measurements on plant and animal cells relied on independent experiments and setups, thus hindering any direct comparison. In this study we used the same micro-rheometer to compare animal and plant single cell rheology. We found that wall-less plant cells exhibit the same weak power law rheology as animal cells, with comparable values of elastic and loss moduli. Remarkably, microtubules primarily contributed to the rheological behavior of wall-less plant cells whereas rheology of animal cells was mainly dependent on the actin network. Thus, plant and animal cells evolved different molecular strategies to reach a comparable cytoplasmic mechanical core, suggesting that evolutionary convergence could include the internal biophysical properties of cells.     

Two non-reactive ternary complexes of estrogenic 17beta-hydroxysteroid dehydrogenase: crystallization and preliminary structural analysis.

Human estrogenic 17β-hydroxysteroid dehydrogenase (17β-HSD1, EC1.1.1.62) is an important enzyme that catalyses the last step of active estrogen formation. 17β-HSD1 plays a key role in the proliferation of breast cancer cells. The three-dimensional structures of this enzyme and of the enzyme-estradiol complex have been solved (Zhu et al., 1993, J. Mol. Biol. 234:242; Ghosh et al., 1995, Structure 3:503; Azzi et al., 1996, Nature Struct. Biol. 3:665). The determination of the non-reactive ternary complex structure, which could mimic the transition state, constitutes a further critical step toward the rational design of inhibitors for this enzyme (Ghosh et al. 1995, Structure 3:503; Penning, 1996, Endocrine-Related Cancer, 3:41).

To further study the transition state, two non-reactive ternary complexes, 17β-HSD1–EM519-NADP⁺ and 17β-HSD1–EM553-NADP⁺ were crystallized using combined methods of soaking and co-crystallization. Although they belong to the same C2 space group, they have different unit cells, with a=155.59 Å, b=42.82 Å, c=121.15 Å, β=128.5° for 17β-HSD1–EM519-NADP⁺, and a=124.01 Å, b=45.16 Å, c=61.40 Å, β=99.2° for 17β-HSD1–EM553-NADP⁺, respectively. Our preliminary results revealed that the inhibitors interact differently with the enzyme than do the natural substrates.