Early defect in branching morphogenesis of the ureteric bud in induced nephron deficit

Early defect in branching morphogenesis of the ureteric bud in induced nephron deficit. Development of the metanephric kidney during embryogenesis can be altered both in vivo and in vitro by exposure to gentamicin, which may lead to oligonephronia. To study the role of the ureteric bud in nephron deficit genesis, we used metanephros organ cultures exposed to gentamicin as a model of impaired nephrogenesis. Ultrastructural localization of the antibiotic showed that by eight hours it was already present within the epithelial cells of the ureteric bud and in its growing ends, and also trapped in the adjacent blastema. Using confocal microscopy and image analysis, we devised a quantitative approach to analyze the branching pattern of the ureteric bud, and showed that by 24 hours of culture, despite no change of explants growth, gentamicin had significantly decreased the number of branching points. This effect involved the early branching events and was limited to end buds that had no nephron anlagen nearby. Our findings indicate that impaired branching morphogenesis of the ureteric bud is the likely event of gentamicin-induced nephron deficit

Distinct domains of the spinal muscular atrophy protein SMN are required for targeting to Cajal bodies in mammalian cells.

Mutations of the survival motor neuron gene SMN1 cause the inherited disease spinal muscular atrophy (SMA). The ubiquitous SMN protein facilitates the biogenesis of spliceosomal small nuclear ribonucleoproteins (snRNPs). The protein is detected in the cytoplasm, nucleoplasm and enriched with snRNPs in nuclear Cajal bodies. It is structurally divided into at least an amino-terminal region rich in basic amino acid residues, a central Tudor domain, a self-association tyrosine-glycine-box and an exon7-encoded C-terminus. To examine the domains required for the intranuclear localization of SMN, we have used fluorescently tagged protein mutants transiently overexpressed in mammalian cells. The basic amino acid residues direct nucleolar localization of SMN mutants. The Tudor domain promotes localization of proteins in the nucleus and it cooperates with the basic amino acid residues and the tyrosine-glycine-box for protein localization in Cajal bodies. Moreover, the most frequent disease-linked mutant SMN{Delta}ex7 reduces accumulation of snRNPs in Cajal bodies, suggesting that the C-terminus of SMN participates in targeting to Cajal bodies. A reduced number of Cajal bodies in patient fibroblasts associates with the absence of snRNPs in Cajal bodies, revealing that intranuclear snRNA organization is modified in disease. These results indicate that direct and indirect mechanisms regulate localization of SMN in Cajal bodies

Are the local adjustments of the relative spatial frequencies of the dynein arms and the beta-tubulin monomers involved in the regulation of the "9+2" axoneme?

International audienceThe "9+2" axoneme is a highly specific cylindrical machine whose periodic bending is due to the cumulative shear of its 9 outer doublets of microtubules. Because of the discrete architecture of the tubulin monomers and the active appendices that the outer doublets carry (dynein arms, nexin links and radial spokes), this movement corresponds to the relative shear of these topological verniers, whose characteristics depend on the geometry of the wave train. When an axonemal segment bends, this induces the compressed and dilated conformations of the tubulin monomers and, consequently, the modification of the spatial frequencies of the appendages that the outer doublets carry. From a dynamic point of view, the adjustments of the spatial frequencies of the elements of the two facing verniers that must interact create different longitudinal periodic patterns of distribution of the joint probability of the molecular interaction as a function of the location of the doublet pairs around the axonemal cylinder and their spatial orientation within the axonemal cylinder. During the shear, these patterns move along the outer doublet intervals at a speed that ranges from one to more than a thousand times that of sliding, in two opposite directions along the two opposite halves of the axoneme separated by the bending plane, respecting the polarity of the dynein arms within the axoneme. Consequently, these waves might be involved in the regulation of the alternating activity of the dynein arms along the flagellum, because they induce the necessary intermolecular dialog along the axoneme since they could be an element of the local dynamic stability/instability equilibrium of the axoneme. This complements the geometric clutch model [Lindemann, C., 1994. A "geometric clutch" hypothesis to explain oscillations of the axoneme of cilia and flagella. J. Theor. Biol. 168, 175-189]

Solubilisation des dyneines ATPases des spermatozoiedes humains normaux incubes en presence de 0.6 M NaCl

SIGLET 54381 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Compliant intervertebral mechanism for humanoid backbone: Kinematic modeling and optimization

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Is the Curvature of the Flagellum Involved in the Apparent Cooperativity of the Dynein Arms along the 9+2 Axoneme?

In a recent study [Cibert, 2008. Journal of Theoretical Biology, 253, 74-89], by assuming that the walls of microtubules are involved in cyclic compression/dilation equilibriums as a consequence of their cyclic curvature of the axoneme, it was proposed that local adjustments of spatial frequencies of both dynein arms and beta-tubulin monomers facing series create propagation of joint probability waves of interaction (JPI) between these two necessary partners. Modeling the occurrence of these interactions along the entire length of an axoneme between each outer doublet pair (without programming any cooperative dialog between the molecular complexes) and the cyclic attachment of two facing partners, we show that such constituted active couples are clustered. Along a cluster the dynein arms exhibit a small phase shift with respect to the order according to which they began their cycle after being linked to a beta-tubulin monomer. The number of couples included in these clusters depends on the probability of interaction between the dynein arms and the beta-tubulin, on the location of the outer doublet pairs around the axonemal cylinder, and on the local bending of the axoneme; around the axonemal cylinder, the faster and the larger the sliding, the shorter the clusters. This mechanism could be involved in the apparent cooperativity of molecular motors and the beta-tubulin monomers, since it is partially controlled by local curvature, and the cluster length is inversely proportional to the sliding activity of the outer doublet pairs they link

Bio-inspired compliant spine for humanoid robot a degrees of freedom challenge

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Mitochondrial respiration and Ca2+ waves are linked during fertilization and meiosis completion

Fertilization increases both cytosolic Ca(2+) concentration and oxygen consumption in the egg but the relationship between these two phenomena remains largely obscure. We have measured mitochondrial oxygen consumption and the mitochondrial NADH concentration on single ascidian eggs and found that they increase in phase with each series of meiotic Ca(2+) waves emitted by two pacemakers (PM1 and PM2). Oxygen consumption also increases in response to Ins(1,4,5)P(3)-induced Ca(2+) transients. Using mitochondrial inhibitors we show that active mitochondria sequester cytosolic Ca(2+) during sperm-triggered Ca(2+) waves and that they are strictly necessary for triggering and sustaining the activity of the meiotic Ca(2+) wave pacemaker PM2. Strikingly, the activity of the Ca(2+) wave pacemaker PM2 can be restored or stimulated by flash photolysis of caged ATP. Taken together our observations provide the first evidence that, in addition to buffering cytosolic Ca(2+), the egg's mitochondria are stimulated by Ins(1,4,5)P(3)-mediated Ca(2+) signals. In turn, mitochondrial ATP production is required to sustain the activity of the meiotic Ca(2+) wave pacemaker PM